forked from OSchip/llvm-project
2200 lines
85 KiB
C++
2200 lines
85 KiB
C++
//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This transformation analyzes and transforms the induction variables (and
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// computations derived from them) into simpler forms suitable for subsequent
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// analysis and transformation.
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//
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// If the trip count of a loop is computable, this pass also makes the following
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// changes:
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// 1. The exit condition for the loop is canonicalized to compare the
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// induction value against the exit value. This turns loops like:
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// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)'
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// 2. Any use outside of the loop of an expression derived from the indvar
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// is changed to compute the derived value outside of the loop, eliminating
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// the dependence on the exit value of the induction variable. If the only
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// purpose of the loop is to compute the exit value of some derived
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// expression, this transformation will make the loop dead.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/LoopUtils.h"
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#include "llvm/Transforms/Utils/SimplifyIndVar.h"
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using namespace llvm;
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#define DEBUG_TYPE "indvars"
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STATISTIC(NumWidened , "Number of indvars widened");
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STATISTIC(NumReplaced , "Number of exit values replaced");
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STATISTIC(NumLFTR , "Number of loop exit tests replaced");
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STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated");
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STATISTIC(NumElimIV , "Number of congruent IVs eliminated");
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// Trip count verification can be enabled by default under NDEBUG if we
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// implement a strong expression equivalence checker in SCEV. Until then, we
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// use the verify-indvars flag, which may assert in some cases.
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static cl::opt<bool> VerifyIndvars(
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"verify-indvars", cl::Hidden,
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cl::desc("Verify the ScalarEvolution result after running indvars"));
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static cl::opt<bool> ReduceLiveIVs("liv-reduce", cl::Hidden,
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cl::desc("Reduce live induction variables."));
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enum ReplaceExitVal { NeverRepl, OnlyCheapRepl, AlwaysRepl };
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static cl::opt<ReplaceExitVal> ReplaceExitValue(
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"replexitval", cl::Hidden, cl::init(OnlyCheapRepl),
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cl::desc("Choose the strategy to replace exit value in IndVarSimplify"),
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cl::values(clEnumValN(NeverRepl, "never", "never replace exit value"),
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clEnumValN(OnlyCheapRepl, "cheap",
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"only replace exit value when the cost is cheap"),
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clEnumValN(AlwaysRepl, "always",
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"always replace exit value whenever possible"),
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clEnumValEnd));
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namespace {
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struct RewritePhi;
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class IndVarSimplify : public LoopPass {
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LoopInfo *LI;
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ScalarEvolution *SE;
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DominatorTree *DT;
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TargetLibraryInfo *TLI;
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const TargetTransformInfo *TTI;
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SmallVector<WeakVH, 16> DeadInsts;
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bool Changed;
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public:
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static char ID; // Pass identification, replacement for typeid
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IndVarSimplify()
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: LoopPass(ID), LI(nullptr), SE(nullptr), DT(nullptr), Changed(false) {
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initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop *L, LPPassManager &LPM) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<LoopInfoWrapperPass>();
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AU.addRequired<ScalarEvolutionWrapperPass>();
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AU.addRequiredID(LoopSimplifyID);
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AU.addRequiredID(LCSSAID);
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AU.addPreserved<GlobalsAAWrapperPass>();
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AU.addPreserved<ScalarEvolutionWrapperPass>();
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AU.addPreservedID(LoopSimplifyID);
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AU.addPreservedID(LCSSAID);
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AU.setPreservesCFG();
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}
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private:
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void releaseMemory() override {
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DeadInsts.clear();
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}
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bool isValidRewrite(Value *FromVal, Value *ToVal);
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void handleFloatingPointIV(Loop *L, PHINode *PH);
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void rewriteNonIntegerIVs(Loop *L);
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void simplifyAndExtend(Loop *L, SCEVExpander &Rewriter, LPPassManager &LPM);
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bool canLoopBeDeleted(Loop *L, SmallVector<RewritePhi, 8> &RewritePhiSet);
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void rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
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Value *linearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
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PHINode *IndVar, SCEVExpander &Rewriter);
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void sinkUnusedInvariants(Loop *L);
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Value *expandSCEVIfNeeded(SCEVExpander &Rewriter, const SCEV *S, Loop *L,
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Instruction *InsertPt, Type *Ty);
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};
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}
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char IndVarSimplify::ID = 0;
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INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
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"Induction Variable Simplification", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_END(IndVarSimplify, "indvars",
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"Induction Variable Simplification", false, false)
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Pass *llvm::createIndVarSimplifyPass() {
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return new IndVarSimplify();
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}
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/// Return true if the SCEV expansion generated by the rewriter can replace the
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/// original value. SCEV guarantees that it produces the same value, but the way
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/// it is produced may be illegal IR. Ideally, this function will only be
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/// called for verification.
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bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
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// If an SCEV expression subsumed multiple pointers, its expansion could
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// reassociate the GEP changing the base pointer. This is illegal because the
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// final address produced by a GEP chain must be inbounds relative to its
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// underlying object. Otherwise basic alias analysis, among other things,
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// could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
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// producing an expression involving multiple pointers. Until then, we must
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// bail out here.
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//
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// Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
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// because it understands lcssa phis while SCEV does not.
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Value *FromPtr = FromVal;
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Value *ToPtr = ToVal;
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if (auto *GEP = dyn_cast<GEPOperator>(FromVal)) {
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FromPtr = GEP->getPointerOperand();
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}
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if (auto *GEP = dyn_cast<GEPOperator>(ToVal)) {
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ToPtr = GEP->getPointerOperand();
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}
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if (FromPtr != FromVal || ToPtr != ToVal) {
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// Quickly check the common case
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if (FromPtr == ToPtr)
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return true;
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// SCEV may have rewritten an expression that produces the GEP's pointer
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// operand. That's ok as long as the pointer operand has the same base
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// pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
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// base of a recurrence. This handles the case in which SCEV expansion
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// converts a pointer type recurrence into a nonrecurrent pointer base
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// indexed by an integer recurrence.
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// If the GEP base pointer is a vector of pointers, abort.
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if (!FromPtr->getType()->isPointerTy() || !ToPtr->getType()->isPointerTy())
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return false;
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const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
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const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
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if (FromBase == ToBase)
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return true;
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DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
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<< *FromBase << " != " << *ToBase << "\n");
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return false;
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}
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return true;
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}
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/// Determine the insertion point for this user. By default, insert immediately
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/// before the user. SCEVExpander or LICM will hoist loop invariants out of the
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/// loop. For PHI nodes, there may be multiple uses, so compute the nearest
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/// common dominator for the incoming blocks.
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static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
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DominatorTree *DT, LoopInfo *LI) {
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PHINode *PHI = dyn_cast<PHINode>(User);
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if (!PHI)
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return User;
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Instruction *InsertPt = nullptr;
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for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
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if (PHI->getIncomingValue(i) != Def)
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continue;
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BasicBlock *InsertBB = PHI->getIncomingBlock(i);
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if (!InsertPt) {
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InsertPt = InsertBB->getTerminator();
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continue;
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}
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InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB);
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InsertPt = InsertBB->getTerminator();
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}
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assert(InsertPt && "Missing phi operand");
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auto *DefI = dyn_cast<Instruction>(Def);
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if (!DefI)
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return InsertPt;
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assert(DT->dominates(DefI, InsertPt) && "def does not dominate all uses");
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auto *L = LI->getLoopFor(DefI->getParent());
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assert(!L || L->contains(LI->getLoopFor(InsertPt->getParent())));
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for (auto *DTN = (*DT)[InsertPt->getParent()]; DTN; DTN = DTN->getIDom())
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if (LI->getLoopFor(DTN->getBlock()) == L)
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return DTN->getBlock()->getTerminator();
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llvm_unreachable("DefI dominates InsertPt!");
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}
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//===----------------------------------------------------------------------===//
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// rewriteNonIntegerIVs and helpers. Prefer integer IVs.
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//===----------------------------------------------------------------------===//
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/// Convert APF to an integer, if possible.
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static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
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bool isExact = false;
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// See if we can convert this to an int64_t
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uint64_t UIntVal;
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if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
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&isExact) != APFloat::opOK || !isExact)
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return false;
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IntVal = UIntVal;
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return true;
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}
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/// If the loop has floating induction variable then insert corresponding
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/// integer induction variable if possible.
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/// For example,
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/// for(double i = 0; i < 10000; ++i)
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/// bar(i)
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/// is converted into
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/// for(int i = 0; i < 10000; ++i)
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/// bar((double)i);
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///
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void IndVarSimplify::handleFloatingPointIV(Loop *L, PHINode *PN) {
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unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
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unsigned BackEdge = IncomingEdge^1;
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// Check incoming value.
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auto *InitValueVal = dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
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int64_t InitValue;
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if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
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return;
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// Check IV increment. Reject this PN if increment operation is not
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// an add or increment value can not be represented by an integer.
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auto *Incr = dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
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if (Incr == nullptr || Incr->getOpcode() != Instruction::FAdd) return;
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// If this is not an add of the PHI with a constantfp, or if the constant fp
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// is not an integer, bail out.
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ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
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int64_t IncValue;
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if (IncValueVal == nullptr || Incr->getOperand(0) != PN ||
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!ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
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return;
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// Check Incr uses. One user is PN and the other user is an exit condition
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// used by the conditional terminator.
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Value::user_iterator IncrUse = Incr->user_begin();
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Instruction *U1 = cast<Instruction>(*IncrUse++);
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if (IncrUse == Incr->user_end()) return;
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Instruction *U2 = cast<Instruction>(*IncrUse++);
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if (IncrUse != Incr->user_end()) return;
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// Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
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// only used by a branch, we can't transform it.
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FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
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if (!Compare)
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Compare = dyn_cast<FCmpInst>(U2);
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if (!Compare || !Compare->hasOneUse() ||
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!isa<BranchInst>(Compare->user_back()))
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return;
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BranchInst *TheBr = cast<BranchInst>(Compare->user_back());
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// We need to verify that the branch actually controls the iteration count
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// of the loop. If not, the new IV can overflow and no one will notice.
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// The branch block must be in the loop and one of the successors must be out
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// of the loop.
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assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
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if (!L->contains(TheBr->getParent()) ||
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(L->contains(TheBr->getSuccessor(0)) &&
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L->contains(TheBr->getSuccessor(1))))
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return;
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// If it isn't a comparison with an integer-as-fp (the exit value), we can't
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// transform it.
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ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
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int64_t ExitValue;
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if (ExitValueVal == nullptr ||
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!ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
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return;
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// Find new predicate for integer comparison.
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CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
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switch (Compare->getPredicate()) {
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default: return; // Unknown comparison.
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case CmpInst::FCMP_OEQ:
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case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
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case CmpInst::FCMP_ONE:
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case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
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case CmpInst::FCMP_OGT:
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case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
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case CmpInst::FCMP_OGE:
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case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
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case CmpInst::FCMP_OLT:
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case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
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case CmpInst::FCMP_OLE:
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case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
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}
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// We convert the floating point induction variable to a signed i32 value if
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// we can. This is only safe if the comparison will not overflow in a way
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// that won't be trapped by the integer equivalent operations. Check for this
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// now.
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// TODO: We could use i64 if it is native and the range requires it.
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// The start/stride/exit values must all fit in signed i32.
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if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
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return;
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// If not actually striding (add x, 0.0), avoid touching the code.
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if (IncValue == 0)
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return;
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// Positive and negative strides have different safety conditions.
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if (IncValue > 0) {
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// If we have a positive stride, we require the init to be less than the
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// exit value.
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if (InitValue >= ExitValue)
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return;
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uint32_t Range = uint32_t(ExitValue-InitValue);
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// Check for infinite loop, either:
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// while (i <= Exit) or until (i > Exit)
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if (NewPred == CmpInst::ICMP_SLE || NewPred == CmpInst::ICMP_SGT) {
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if (++Range == 0) return; // Range overflows.
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}
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unsigned Leftover = Range % uint32_t(IncValue);
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// If this is an equality comparison, we require that the strided value
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// exactly land on the exit value, otherwise the IV condition will wrap
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// around and do things the fp IV wouldn't.
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if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
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Leftover != 0)
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return;
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// If the stride would wrap around the i32 before exiting, we can't
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// transform the IV.
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if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
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return;
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} else {
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// If we have a negative stride, we require the init to be greater than the
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// exit value.
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if (InitValue <= ExitValue)
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return;
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uint32_t Range = uint32_t(InitValue-ExitValue);
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// Check for infinite loop, either:
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// while (i >= Exit) or until (i < Exit)
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if (NewPred == CmpInst::ICMP_SGE || NewPred == CmpInst::ICMP_SLT) {
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if (++Range == 0) return; // Range overflows.
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}
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unsigned Leftover = Range % uint32_t(-IncValue);
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// If this is an equality comparison, we require that the strided value
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// exactly land on the exit value, otherwise the IV condition will wrap
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// around and do things the fp IV wouldn't.
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if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
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Leftover != 0)
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return;
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// If the stride would wrap around the i32 before exiting, we can't
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// transform the IV.
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if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
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return;
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}
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IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
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// Insert new integer induction variable.
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PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
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NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
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PN->getIncomingBlock(IncomingEdge));
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Value *NewAdd =
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BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
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Incr->getName()+".int", Incr);
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NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
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ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
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ConstantInt::get(Int32Ty, ExitValue),
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Compare->getName());
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// In the following deletions, PN may become dead and may be deleted.
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// Use a WeakVH to observe whether this happens.
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WeakVH WeakPH = PN;
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// Delete the old floating point exit comparison. The branch starts using the
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// new comparison.
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NewCompare->takeName(Compare);
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Compare->replaceAllUsesWith(NewCompare);
|
|
RecursivelyDeleteTriviallyDeadInstructions(Compare, TLI);
|
|
|
|
// Delete the old floating point increment.
|
|
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
|
|
RecursivelyDeleteTriviallyDeadInstructions(Incr, TLI);
|
|
|
|
// If the FP induction variable still has uses, this is because something else
|
|
// in the loop uses its value. In order to canonicalize the induction
|
|
// variable, we chose to eliminate the IV and rewrite it in terms of an
|
|
// int->fp cast.
|
|
//
|
|
// We give preference to sitofp over uitofp because it is faster on most
|
|
// platforms.
|
|
if (WeakPH) {
|
|
Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
|
|
&*PN->getParent()->getFirstInsertionPt());
|
|
PN->replaceAllUsesWith(Conv);
|
|
RecursivelyDeleteTriviallyDeadInstructions(PN, TLI);
|
|
}
|
|
Changed = true;
|
|
}
|
|
|
|
void IndVarSimplify::rewriteNonIntegerIVs(Loop *L) {
|
|
// First step. Check to see if there are any floating-point recurrences.
|
|
// If there are, change them into integer recurrences, permitting analysis by
|
|
// the SCEV routines.
|
|
//
|
|
BasicBlock *Header = L->getHeader();
|
|
|
|
SmallVector<WeakVH, 8> PHIs;
|
|
for (BasicBlock::iterator I = Header->begin();
|
|
PHINode *PN = dyn_cast<PHINode>(I); ++I)
|
|
PHIs.push_back(PN);
|
|
|
|
for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
|
|
if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
|
|
handleFloatingPointIV(L, PN);
|
|
|
|
// If the loop previously had floating-point IV, ScalarEvolution
|
|
// may not have been able to compute a trip count. Now that we've done some
|
|
// re-writing, the trip count may be computable.
|
|
if (Changed)
|
|
SE->forgetLoop(L);
|
|
}
|
|
|
|
namespace {
|
|
// Collect information about PHI nodes which can be transformed in
|
|
// rewriteLoopExitValues.
|
|
struct RewritePhi {
|
|
PHINode *PN;
|
|
unsigned Ith; // Ith incoming value.
|
|
Value *Val; // Exit value after expansion.
|
|
bool HighCost; // High Cost when expansion.
|
|
bool SafePhi; // LCSSASafePhiForRAUW.
|
|
|
|
RewritePhi(PHINode *P, unsigned I, Value *V, bool H, bool S)
|
|
: PN(P), Ith(I), Val(V), HighCost(H), SafePhi(S) {}
|
|
};
|
|
}
|
|
|
|
Value *IndVarSimplify::expandSCEVIfNeeded(SCEVExpander &Rewriter, const SCEV *S,
|
|
Loop *L, Instruction *InsertPt,
|
|
Type *ResultTy) {
|
|
// Before expanding S into an expensive LLVM expression, see if we can use an
|
|
// already existing value as the expansion for S.
|
|
if (Value *ExistingValue = Rewriter.findExistingExpansion(S, InsertPt, L))
|
|
if (ExistingValue->getType() == ResultTy)
|
|
return ExistingValue;
|
|
|
|
// We didn't find anything, fall back to using SCEVExpander.
|
|
return Rewriter.expandCodeFor(S, ResultTy, InsertPt);
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// rewriteLoopExitValues - Optimize IV users outside the loop.
|
|
// As a side effect, reduces the amount of IV processing within the loop.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// Check to see if this loop has a computable loop-invariant execution count.
|
|
/// If so, this means that we can compute the final value of any expressions
|
|
/// that are recurrent in the loop, and substitute the exit values from the loop
|
|
/// into any instructions outside of the loop that use the final values of the
|
|
/// current expressions.
|
|
///
|
|
/// This is mostly redundant with the regular IndVarSimplify activities that
|
|
/// happen later, except that it's more powerful in some cases, because it's
|
|
/// able to brute-force evaluate arbitrary instructions as long as they have
|
|
/// constant operands at the beginning of the loop.
|
|
void IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
|
|
// Check a pre-condition.
|
|
assert(L->isRecursivelyLCSSAForm(*DT) && "Indvars did not preserve LCSSA!");
|
|
|
|
SmallVector<BasicBlock*, 8> ExitBlocks;
|
|
L->getUniqueExitBlocks(ExitBlocks);
|
|
|
|
SmallVector<RewritePhi, 8> RewritePhiSet;
|
|
// Find all values that are computed inside the loop, but used outside of it.
|
|
// Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
|
|
// the exit blocks of the loop to find them.
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *ExitBB = ExitBlocks[i];
|
|
|
|
// If there are no PHI nodes in this exit block, then no values defined
|
|
// inside the loop are used on this path, skip it.
|
|
PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
|
|
if (!PN) continue;
|
|
|
|
unsigned NumPreds = PN->getNumIncomingValues();
|
|
|
|
// We would like to be able to RAUW single-incoming value PHI nodes. We
|
|
// have to be certain this is safe even when this is an LCSSA PHI node.
|
|
// While the computed exit value is no longer varying in *this* loop, the
|
|
// exit block may be an exit block for an outer containing loop as well,
|
|
// the exit value may be varying in the outer loop, and thus it may still
|
|
// require an LCSSA PHI node. The safe case is when this is
|
|
// single-predecessor PHI node (LCSSA) and the exit block containing it is
|
|
// part of the enclosing loop, or this is the outer most loop of the nest.
|
|
// In either case the exit value could (at most) be varying in the same
|
|
// loop body as the phi node itself. Thus if it is in turn used outside of
|
|
// an enclosing loop it will only be via a separate LCSSA node.
|
|
bool LCSSASafePhiForRAUW =
|
|
NumPreds == 1 &&
|
|
(!L->getParentLoop() || L->getParentLoop() == LI->getLoopFor(ExitBB));
|
|
|
|
// Iterate over all of the PHI nodes.
|
|
BasicBlock::iterator BBI = ExitBB->begin();
|
|
while ((PN = dyn_cast<PHINode>(BBI++))) {
|
|
if (PN->use_empty())
|
|
continue; // dead use, don't replace it
|
|
|
|
// SCEV only supports integer expressions for now.
|
|
if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
|
|
continue;
|
|
|
|
// It's necessary to tell ScalarEvolution about this explicitly so that
|
|
// it can walk the def-use list and forget all SCEVs, as it may not be
|
|
// watching the PHI itself. Once the new exit value is in place, there
|
|
// may not be a def-use connection between the loop and every instruction
|
|
// which got a SCEVAddRecExpr for that loop.
|
|
SE->forgetValue(PN);
|
|
|
|
// Iterate over all of the values in all the PHI nodes.
|
|
for (unsigned i = 0; i != NumPreds; ++i) {
|
|
// If the value being merged in is not integer or is not defined
|
|
// in the loop, skip it.
|
|
Value *InVal = PN->getIncomingValue(i);
|
|
if (!isa<Instruction>(InVal))
|
|
continue;
|
|
|
|
// If this pred is for a subloop, not L itself, skip it.
|
|
if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
|
|
continue; // The Block is in a subloop, skip it.
|
|
|
|
// Check that InVal is defined in the loop.
|
|
Instruction *Inst = cast<Instruction>(InVal);
|
|
if (!L->contains(Inst))
|
|
continue;
|
|
|
|
// Okay, this instruction has a user outside of the current loop
|
|
// and varies predictably *inside* the loop. Evaluate the value it
|
|
// contains when the loop exits, if possible.
|
|
const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
|
|
if (!SE->isLoopInvariant(ExitValue, L) ||
|
|
!isSafeToExpand(ExitValue, *SE))
|
|
continue;
|
|
|
|
// Computing the value outside of the loop brings no benefit if :
|
|
// - it is definitely used inside the loop in a way which can not be
|
|
// optimized away.
|
|
// - no use outside of the loop can take advantage of hoisting the
|
|
// computation out of the loop
|
|
if (ExitValue->getSCEVType()>=scMulExpr) {
|
|
unsigned NumHardInternalUses = 0;
|
|
unsigned NumSoftExternalUses = 0;
|
|
unsigned NumUses = 0;
|
|
for (auto IB = Inst->user_begin(), IE = Inst->user_end();
|
|
IB != IE && NumUses <= 6; ++IB) {
|
|
Instruction *UseInstr = cast<Instruction>(*IB);
|
|
unsigned Opc = UseInstr->getOpcode();
|
|
NumUses++;
|
|
if (L->contains(UseInstr)) {
|
|
if (Opc == Instruction::Call || Opc == Instruction::Ret)
|
|
NumHardInternalUses++;
|
|
} else {
|
|
if (Opc == Instruction::PHI) {
|
|
// Do not count the Phi as a use. LCSSA may have inserted
|
|
// plenty of trivial ones.
|
|
NumUses--;
|
|
for (auto PB = UseInstr->user_begin(),
|
|
PE = UseInstr->user_end();
|
|
PB != PE && NumUses <= 6; ++PB, ++NumUses) {
|
|
unsigned PhiOpc = cast<Instruction>(*PB)->getOpcode();
|
|
if (PhiOpc != Instruction::Call && PhiOpc != Instruction::Ret)
|
|
NumSoftExternalUses++;
|
|
}
|
|
continue;
|
|
}
|
|
if (Opc != Instruction::Call && Opc != Instruction::Ret)
|
|
NumSoftExternalUses++;
|
|
}
|
|
}
|
|
if (NumUses <= 6 && NumHardInternalUses && !NumSoftExternalUses)
|
|
continue;
|
|
}
|
|
|
|
bool HighCost = Rewriter.isHighCostExpansion(ExitValue, L, Inst);
|
|
Value *ExitVal =
|
|
expandSCEVIfNeeded(Rewriter, ExitValue, L, Inst, PN->getType());
|
|
|
|
DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
|
|
<< " LoopVal = " << *Inst << "\n");
|
|
|
|
if (!isValidRewrite(Inst, ExitVal)) {
|
|
DeadInsts.push_back(ExitVal);
|
|
continue;
|
|
}
|
|
|
|
// Collect all the candidate PHINodes to be rewritten.
|
|
RewritePhiSet.push_back(
|
|
RewritePhi(PN, i, ExitVal, HighCost, LCSSASafePhiForRAUW));
|
|
}
|
|
}
|
|
}
|
|
|
|
bool LoopCanBeDel = canLoopBeDeleted(L, RewritePhiSet);
|
|
|
|
// Transformation.
|
|
for (const RewritePhi &Phi : RewritePhiSet) {
|
|
PHINode *PN = Phi.PN;
|
|
Value *ExitVal = Phi.Val;
|
|
|
|
// Only do the rewrite when the ExitValue can be expanded cheaply.
|
|
// If LoopCanBeDel is true, rewrite exit value aggressively.
|
|
if (ReplaceExitValue == OnlyCheapRepl && !LoopCanBeDel && Phi.HighCost) {
|
|
DeadInsts.push_back(ExitVal);
|
|
continue;
|
|
}
|
|
|
|
Changed = true;
|
|
++NumReplaced;
|
|
Instruction *Inst = cast<Instruction>(PN->getIncomingValue(Phi.Ith));
|
|
PN->setIncomingValue(Phi.Ith, ExitVal);
|
|
|
|
// If this instruction is dead now, delete it. Don't do it now to avoid
|
|
// invalidating iterators.
|
|
if (isInstructionTriviallyDead(Inst, TLI))
|
|
DeadInsts.push_back(Inst);
|
|
|
|
// If we determined that this PHI is safe to replace even if an LCSSA
|
|
// PHI, do so.
|
|
if (Phi.SafePhi) {
|
|
PN->replaceAllUsesWith(ExitVal);
|
|
PN->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
// The insertion point instruction may have been deleted; clear it out
|
|
// so that the rewriter doesn't trip over it later.
|
|
Rewriter.clearInsertPoint();
|
|
}
|
|
|
|
/// Check whether it is possible to delete the loop after rewriting exit
|
|
/// value. If it is possible, ignore ReplaceExitValue and do rewriting
|
|
/// aggressively.
|
|
bool IndVarSimplify::canLoopBeDeleted(
|
|
Loop *L, SmallVector<RewritePhi, 8> &RewritePhiSet) {
|
|
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
// If there is no preheader, the loop will not be deleted.
|
|
if (!Preheader)
|
|
return false;
|
|
|
|
// In LoopDeletion pass Loop can be deleted when ExitingBlocks.size() > 1.
|
|
// We obviate multiple ExitingBlocks case for simplicity.
|
|
// TODO: If we see testcase with multiple ExitingBlocks can be deleted
|
|
// after exit value rewriting, we can enhance the logic here.
|
|
SmallVector<BasicBlock *, 4> ExitingBlocks;
|
|
L->getExitingBlocks(ExitingBlocks);
|
|
SmallVector<BasicBlock *, 8> ExitBlocks;
|
|
L->getUniqueExitBlocks(ExitBlocks);
|
|
if (ExitBlocks.size() > 1 || ExitingBlocks.size() > 1)
|
|
return false;
|
|
|
|
BasicBlock *ExitBlock = ExitBlocks[0];
|
|
BasicBlock::iterator BI = ExitBlock->begin();
|
|
while (PHINode *P = dyn_cast<PHINode>(BI)) {
|
|
Value *Incoming = P->getIncomingValueForBlock(ExitingBlocks[0]);
|
|
|
|
// If the Incoming value of P is found in RewritePhiSet, we know it
|
|
// could be rewritten to use a loop invariant value in transformation
|
|
// phase later. Skip it in the loop invariant check below.
|
|
bool found = false;
|
|
for (const RewritePhi &Phi : RewritePhiSet) {
|
|
unsigned i = Phi.Ith;
|
|
if (Phi.PN == P && (Phi.PN)->getIncomingValue(i) == Incoming) {
|
|
found = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
Instruction *I;
|
|
if (!found && (I = dyn_cast<Instruction>(Incoming)))
|
|
if (!L->hasLoopInvariantOperands(I))
|
|
return false;
|
|
|
|
++BI;
|
|
}
|
|
|
|
for (auto *BB : L->blocks())
|
|
if (any_of(*BB, [](Instruction &I) { return I.mayHaveSideEffects(); }))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// IV Widening - Extend the width of an IV to cover its widest uses.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
namespace {
|
|
// Collect information about induction variables that are used by sign/zero
|
|
// extend operations. This information is recorded by CollectExtend and provides
|
|
// the input to WidenIV.
|
|
struct WideIVInfo {
|
|
PHINode *NarrowIV = nullptr;
|
|
Type *WidestNativeType = nullptr; // Widest integer type created [sz]ext
|
|
bool IsSigned = false; // Was a sext user seen before a zext?
|
|
};
|
|
}
|
|
|
|
/// Update information about the induction variable that is extended by this
|
|
/// sign or zero extend operation. This is used to determine the final width of
|
|
/// the IV before actually widening it.
|
|
static void visitIVCast(CastInst *Cast, WideIVInfo &WI, ScalarEvolution *SE,
|
|
const TargetTransformInfo *TTI) {
|
|
bool IsSigned = Cast->getOpcode() == Instruction::SExt;
|
|
if (!IsSigned && Cast->getOpcode() != Instruction::ZExt)
|
|
return;
|
|
|
|
Type *Ty = Cast->getType();
|
|
uint64_t Width = SE->getTypeSizeInBits(Ty);
|
|
if (!Cast->getModule()->getDataLayout().isLegalInteger(Width))
|
|
return;
|
|
|
|
// Cast is either an sext or zext up to this point.
|
|
// We should not widen an indvar if arithmetics on the wider indvar are more
|
|
// expensive than those on the narrower indvar. We check only the cost of ADD
|
|
// because at least an ADD is required to increment the induction variable. We
|
|
// could compute more comprehensively the cost of all instructions on the
|
|
// induction variable when necessary.
|
|
if (TTI &&
|
|
TTI->getArithmeticInstrCost(Instruction::Add, Ty) >
|
|
TTI->getArithmeticInstrCost(Instruction::Add,
|
|
Cast->getOperand(0)->getType())) {
|
|
return;
|
|
}
|
|
|
|
if (!WI.WidestNativeType) {
|
|
WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
|
|
WI.IsSigned = IsSigned;
|
|
return;
|
|
}
|
|
|
|
// We extend the IV to satisfy the sign of its first user, arbitrarily.
|
|
if (WI.IsSigned != IsSigned)
|
|
return;
|
|
|
|
if (Width > SE->getTypeSizeInBits(WI.WidestNativeType))
|
|
WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
|
|
}
|
|
|
|
namespace {
|
|
|
|
/// Record a link in the Narrow IV def-use chain along with the WideIV that
|
|
/// computes the same value as the Narrow IV def. This avoids caching Use*
|
|
/// pointers.
|
|
struct NarrowIVDefUse {
|
|
Instruction *NarrowDef = nullptr;
|
|
Instruction *NarrowUse = nullptr;
|
|
Instruction *WideDef = nullptr;
|
|
|
|
// True if the narrow def is never negative. Tracking this information lets
|
|
// us use a sign extension instead of a zero extension or vice versa, when
|
|
// profitable and legal.
|
|
bool NeverNegative = false;
|
|
|
|
NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD,
|
|
bool NeverNegative)
|
|
: NarrowDef(ND), NarrowUse(NU), WideDef(WD),
|
|
NeverNegative(NeverNegative) {}
|
|
};
|
|
|
|
/// The goal of this transform is to remove sign and zero extends without
|
|
/// creating any new induction variables. To do this, it creates a new phi of
|
|
/// the wider type and redirects all users, either removing extends or inserting
|
|
/// truncs whenever we stop propagating the type.
|
|
///
|
|
class WidenIV {
|
|
// Parameters
|
|
PHINode *OrigPhi;
|
|
Type *WideType;
|
|
bool IsSigned;
|
|
|
|
// Context
|
|
LoopInfo *LI;
|
|
Loop *L;
|
|
ScalarEvolution *SE;
|
|
DominatorTree *DT;
|
|
|
|
// Result
|
|
PHINode *WidePhi;
|
|
Instruction *WideInc;
|
|
const SCEV *WideIncExpr;
|
|
SmallVectorImpl<WeakVH> &DeadInsts;
|
|
|
|
SmallPtrSet<Instruction*,16> Widened;
|
|
SmallVector<NarrowIVDefUse, 8> NarrowIVUsers;
|
|
|
|
public:
|
|
WidenIV(const WideIVInfo &WI, LoopInfo *LInfo,
|
|
ScalarEvolution *SEv, DominatorTree *DTree,
|
|
SmallVectorImpl<WeakVH> &DI) :
|
|
OrigPhi(WI.NarrowIV),
|
|
WideType(WI.WidestNativeType),
|
|
IsSigned(WI.IsSigned),
|
|
LI(LInfo),
|
|
L(LI->getLoopFor(OrigPhi->getParent())),
|
|
SE(SEv),
|
|
DT(DTree),
|
|
WidePhi(nullptr),
|
|
WideInc(nullptr),
|
|
WideIncExpr(nullptr),
|
|
DeadInsts(DI) {
|
|
assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
|
|
}
|
|
|
|
PHINode *createWideIV(SCEVExpander &Rewriter);
|
|
|
|
protected:
|
|
Value *createExtendInst(Value *NarrowOper, Type *WideType, bool IsSigned,
|
|
Instruction *Use);
|
|
|
|
Instruction *cloneIVUser(NarrowIVDefUse DU, const SCEVAddRecExpr *WideAR);
|
|
Instruction *cloneArithmeticIVUser(NarrowIVDefUse DU,
|
|
const SCEVAddRecExpr *WideAR);
|
|
Instruction *cloneBitwiseIVUser(NarrowIVDefUse DU);
|
|
|
|
const SCEVAddRecExpr *getWideRecurrence(Instruction *NarrowUse);
|
|
|
|
const SCEVAddRecExpr* getExtendedOperandRecurrence(NarrowIVDefUse DU);
|
|
|
|
const SCEV *getSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
|
|
unsigned OpCode) const;
|
|
|
|
Instruction *widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter);
|
|
|
|
bool widenLoopCompare(NarrowIVDefUse DU);
|
|
|
|
void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
|
|
};
|
|
} // anonymous namespace
|
|
|
|
/// Perform a quick domtree based check for loop invariance assuming that V is
|
|
/// used within the loop. LoopInfo::isLoopInvariant() seems gratuitous for this
|
|
/// purpose.
|
|
static bool isLoopInvariant(Value *V, const Loop *L, const DominatorTree *DT) {
|
|
Instruction *Inst = dyn_cast<Instruction>(V);
|
|
if (!Inst)
|
|
return true;
|
|
|
|
return DT->properlyDominates(Inst->getParent(), L->getHeader());
|
|
}
|
|
|
|
Value *WidenIV::createExtendInst(Value *NarrowOper, Type *WideType,
|
|
bool IsSigned, Instruction *Use) {
|
|
// Set the debug location and conservative insertion point.
|
|
IRBuilder<> Builder(Use);
|
|
// Hoist the insertion point into loop preheaders as far as possible.
|
|
for (const Loop *L = LI->getLoopFor(Use->getParent());
|
|
L && L->getLoopPreheader() && isLoopInvariant(NarrowOper, L, DT);
|
|
L = L->getParentLoop())
|
|
Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator());
|
|
|
|
return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
|
|
Builder.CreateZExt(NarrowOper, WideType);
|
|
}
|
|
|
|
/// Instantiate a wide operation to replace a narrow operation. This only needs
|
|
/// to handle operations that can evaluation to SCEVAddRec. It can safely return
|
|
/// 0 for any operation we decide not to clone.
|
|
Instruction *WidenIV::cloneIVUser(NarrowIVDefUse DU,
|
|
const SCEVAddRecExpr *WideAR) {
|
|
unsigned Opcode = DU.NarrowUse->getOpcode();
|
|
switch (Opcode) {
|
|
default:
|
|
return nullptr;
|
|
case Instruction::Add:
|
|
case Instruction::Mul:
|
|
case Instruction::UDiv:
|
|
case Instruction::Sub:
|
|
return cloneArithmeticIVUser(DU, WideAR);
|
|
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor:
|
|
case Instruction::Shl:
|
|
case Instruction::LShr:
|
|
case Instruction::AShr:
|
|
return cloneBitwiseIVUser(DU);
|
|
}
|
|
}
|
|
|
|
Instruction *WidenIV::cloneBitwiseIVUser(NarrowIVDefUse DU) {
|
|
Instruction *NarrowUse = DU.NarrowUse;
|
|
Instruction *NarrowDef = DU.NarrowDef;
|
|
Instruction *WideDef = DU.WideDef;
|
|
|
|
DEBUG(dbgs() << "Cloning bitwise IVUser: " << *NarrowUse << "\n");
|
|
|
|
// Replace NarrowDef operands with WideDef. Otherwise, we don't know anything
|
|
// about the narrow operand yet so must insert a [sz]ext. It is probably loop
|
|
// invariant and will be folded or hoisted. If it actually comes from a
|
|
// widened IV, it should be removed during a future call to widenIVUse.
|
|
Value *LHS = (NarrowUse->getOperand(0) == NarrowDef)
|
|
? WideDef
|
|
: createExtendInst(NarrowUse->getOperand(0), WideType,
|
|
IsSigned, NarrowUse);
|
|
Value *RHS = (NarrowUse->getOperand(1) == NarrowDef)
|
|
? WideDef
|
|
: createExtendInst(NarrowUse->getOperand(1), WideType,
|
|
IsSigned, NarrowUse);
|
|
|
|
auto *NarrowBO = cast<BinaryOperator>(NarrowUse);
|
|
auto *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), LHS, RHS,
|
|
NarrowBO->getName());
|
|
IRBuilder<> Builder(NarrowUse);
|
|
Builder.Insert(WideBO);
|
|
WideBO->copyIRFlags(NarrowBO);
|
|
return WideBO;
|
|
}
|
|
|
|
Instruction *WidenIV::cloneArithmeticIVUser(NarrowIVDefUse DU,
|
|
const SCEVAddRecExpr *WideAR) {
|
|
Instruction *NarrowUse = DU.NarrowUse;
|
|
Instruction *NarrowDef = DU.NarrowDef;
|
|
Instruction *WideDef = DU.WideDef;
|
|
|
|
DEBUG(dbgs() << "Cloning arithmetic IVUser: " << *NarrowUse << "\n");
|
|
|
|
unsigned IVOpIdx = (NarrowUse->getOperand(0) == NarrowDef) ? 0 : 1;
|
|
|
|
// We're trying to find X such that
|
|
//
|
|
// Widen(NarrowDef `op` NonIVNarrowDef) == WideAR == WideDef `op.wide` X
|
|
//
|
|
// We guess two solutions to X, sext(NonIVNarrowDef) and zext(NonIVNarrowDef),
|
|
// and check using SCEV if any of them are correct.
|
|
|
|
// Returns true if extending NonIVNarrowDef according to `SignExt` is a
|
|
// correct solution to X.
|
|
auto GuessNonIVOperand = [&](bool SignExt) {
|
|
const SCEV *WideLHS;
|
|
const SCEV *WideRHS;
|
|
|
|
auto GetExtend = [this, SignExt](const SCEV *S, Type *Ty) {
|
|
if (SignExt)
|
|
return SE->getSignExtendExpr(S, Ty);
|
|
return SE->getZeroExtendExpr(S, Ty);
|
|
};
|
|
|
|
if (IVOpIdx == 0) {
|
|
WideLHS = SE->getSCEV(WideDef);
|
|
const SCEV *NarrowRHS = SE->getSCEV(NarrowUse->getOperand(1));
|
|
WideRHS = GetExtend(NarrowRHS, WideType);
|
|
} else {
|
|
const SCEV *NarrowLHS = SE->getSCEV(NarrowUse->getOperand(0));
|
|
WideLHS = GetExtend(NarrowLHS, WideType);
|
|
WideRHS = SE->getSCEV(WideDef);
|
|
}
|
|
|
|
// WideUse is "WideDef `op.wide` X" as described in the comment.
|
|
const SCEV *WideUse = nullptr;
|
|
|
|
switch (NarrowUse->getOpcode()) {
|
|
default:
|
|
llvm_unreachable("No other possibility!");
|
|
|
|
case Instruction::Add:
|
|
WideUse = SE->getAddExpr(WideLHS, WideRHS);
|
|
break;
|
|
|
|
case Instruction::Mul:
|
|
WideUse = SE->getMulExpr(WideLHS, WideRHS);
|
|
break;
|
|
|
|
case Instruction::UDiv:
|
|
WideUse = SE->getUDivExpr(WideLHS, WideRHS);
|
|
break;
|
|
|
|
case Instruction::Sub:
|
|
WideUse = SE->getMinusSCEV(WideLHS, WideRHS);
|
|
break;
|
|
}
|
|
|
|
return WideUse == WideAR;
|
|
};
|
|
|
|
bool SignExtend = IsSigned;
|
|
if (!GuessNonIVOperand(SignExtend)) {
|
|
SignExtend = !SignExtend;
|
|
if (!GuessNonIVOperand(SignExtend))
|
|
return nullptr;
|
|
}
|
|
|
|
Value *LHS = (NarrowUse->getOperand(0) == NarrowDef)
|
|
? WideDef
|
|
: createExtendInst(NarrowUse->getOperand(0), WideType,
|
|
SignExtend, NarrowUse);
|
|
Value *RHS = (NarrowUse->getOperand(1) == NarrowDef)
|
|
? WideDef
|
|
: createExtendInst(NarrowUse->getOperand(1), WideType,
|
|
SignExtend, NarrowUse);
|
|
|
|
auto *NarrowBO = cast<BinaryOperator>(NarrowUse);
|
|
auto *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), LHS, RHS,
|
|
NarrowBO->getName());
|
|
|
|
IRBuilder<> Builder(NarrowUse);
|
|
Builder.Insert(WideBO);
|
|
WideBO->copyIRFlags(NarrowBO);
|
|
return WideBO;
|
|
}
|
|
|
|
const SCEV *WidenIV::getSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
|
|
unsigned OpCode) const {
|
|
if (OpCode == Instruction::Add)
|
|
return SE->getAddExpr(LHS, RHS);
|
|
if (OpCode == Instruction::Sub)
|
|
return SE->getMinusSCEV(LHS, RHS);
|
|
if (OpCode == Instruction::Mul)
|
|
return SE->getMulExpr(LHS, RHS);
|
|
|
|
llvm_unreachable("Unsupported opcode.");
|
|
}
|
|
|
|
/// No-wrap operations can transfer sign extension of their result to their
|
|
/// operands. Generate the SCEV value for the widened operation without
|
|
/// actually modifying the IR yet. If the expression after extending the
|
|
/// operands is an AddRec for this loop, return it.
|
|
const SCEVAddRecExpr* WidenIV::getExtendedOperandRecurrence(NarrowIVDefUse DU) {
|
|
|
|
// Handle the common case of add<nsw/nuw>
|
|
const unsigned OpCode = DU.NarrowUse->getOpcode();
|
|
// Only Add/Sub/Mul instructions supported yet.
|
|
if (OpCode != Instruction::Add && OpCode != Instruction::Sub &&
|
|
OpCode != Instruction::Mul)
|
|
return nullptr;
|
|
|
|
// One operand (NarrowDef) has already been extended to WideDef. Now determine
|
|
// if extending the other will lead to a recurrence.
|
|
const unsigned ExtendOperIdx =
|
|
DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
|
|
assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU");
|
|
|
|
const SCEV *ExtendOperExpr = nullptr;
|
|
const OverflowingBinaryOperator *OBO =
|
|
cast<OverflowingBinaryOperator>(DU.NarrowUse);
|
|
if (IsSigned && OBO->hasNoSignedWrap())
|
|
ExtendOperExpr = SE->getSignExtendExpr(
|
|
SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
|
|
else if(!IsSigned && OBO->hasNoUnsignedWrap())
|
|
ExtendOperExpr = SE->getZeroExtendExpr(
|
|
SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
|
|
else
|
|
return nullptr;
|
|
|
|
// When creating this SCEV expr, don't apply the current operations NSW or NUW
|
|
// flags. This instruction may be guarded by control flow that the no-wrap
|
|
// behavior depends on. Non-control-equivalent instructions can be mapped to
|
|
// the same SCEV expression, and it would be incorrect to transfer NSW/NUW
|
|
// semantics to those operations.
|
|
const SCEV *lhs = SE->getSCEV(DU.WideDef);
|
|
const SCEV *rhs = ExtendOperExpr;
|
|
|
|
// Let's swap operands to the initial order for the case of non-commutative
|
|
// operations, like SUB. See PR21014.
|
|
if (ExtendOperIdx == 0)
|
|
std::swap(lhs, rhs);
|
|
const SCEVAddRecExpr *AddRec =
|
|
dyn_cast<SCEVAddRecExpr>(getSCEVByOpCode(lhs, rhs, OpCode));
|
|
|
|
if (!AddRec || AddRec->getLoop() != L)
|
|
return nullptr;
|
|
return AddRec;
|
|
}
|
|
|
|
/// Is this instruction potentially interesting for further simplification after
|
|
/// widening it's type? In other words, can the extend be safely hoisted out of
|
|
/// the loop with SCEV reducing the value to a recurrence on the same loop. If
|
|
/// so, return the sign or zero extended recurrence. Otherwise return NULL.
|
|
const SCEVAddRecExpr *WidenIV::getWideRecurrence(Instruction *NarrowUse) {
|
|
if (!SE->isSCEVable(NarrowUse->getType()))
|
|
return nullptr;
|
|
|
|
const SCEV *NarrowExpr = SE->getSCEV(NarrowUse);
|
|
if (SE->getTypeSizeInBits(NarrowExpr->getType())
|
|
>= SE->getTypeSizeInBits(WideType)) {
|
|
// NarrowUse implicitly widens its operand. e.g. a gep with a narrow
|
|
// index. So don't follow this use.
|
|
return nullptr;
|
|
}
|
|
|
|
const SCEV *WideExpr = IsSigned ?
|
|
SE->getSignExtendExpr(NarrowExpr, WideType) :
|
|
SE->getZeroExtendExpr(NarrowExpr, WideType);
|
|
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
|
|
if (!AddRec || AddRec->getLoop() != L)
|
|
return nullptr;
|
|
return AddRec;
|
|
}
|
|
|
|
/// This IV user cannot be widen. Replace this use of the original narrow IV
|
|
/// with a truncation of the new wide IV to isolate and eliminate the narrow IV.
|
|
static void truncateIVUse(NarrowIVDefUse DU, DominatorTree *DT, LoopInfo *LI) {
|
|
DEBUG(dbgs() << "INDVARS: Truncate IV " << *DU.WideDef
|
|
<< " for user " << *DU.NarrowUse << "\n");
|
|
IRBuilder<> Builder(
|
|
getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT, LI));
|
|
Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
|
|
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
|
|
}
|
|
|
|
/// If the narrow use is a compare instruction, then widen the compare
|
|
// (and possibly the other operand). The extend operation is hoisted into the
|
|
// loop preheader as far as possible.
|
|
bool WidenIV::widenLoopCompare(NarrowIVDefUse DU) {
|
|
ICmpInst *Cmp = dyn_cast<ICmpInst>(DU.NarrowUse);
|
|
if (!Cmp)
|
|
return false;
|
|
|
|
// We can legally widen the comparison in the following two cases:
|
|
//
|
|
// - The signedness of the IV extension and comparison match
|
|
//
|
|
// - The narrow IV is always positive (and thus its sign extension is equal
|
|
// to its zero extension). For instance, let's say we're zero extending
|
|
// %narrow for the following use
|
|
//
|
|
// icmp slt i32 %narrow, %val ... (A)
|
|
//
|
|
// and %narrow is always positive. Then
|
|
//
|
|
// (A) == icmp slt i32 sext(%narrow), sext(%val)
|
|
// == icmp slt i32 zext(%narrow), sext(%val)
|
|
|
|
if (!(DU.NeverNegative || IsSigned == Cmp->isSigned()))
|
|
return false;
|
|
|
|
Value *Op = Cmp->getOperand(Cmp->getOperand(0) == DU.NarrowDef ? 1 : 0);
|
|
unsigned CastWidth = SE->getTypeSizeInBits(Op->getType());
|
|
unsigned IVWidth = SE->getTypeSizeInBits(WideType);
|
|
assert (CastWidth <= IVWidth && "Unexpected width while widening compare.");
|
|
|
|
// Widen the compare instruction.
|
|
IRBuilder<> Builder(
|
|
getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT, LI));
|
|
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
|
|
|
|
// Widen the other operand of the compare, if necessary.
|
|
if (CastWidth < IVWidth) {
|
|
Value *ExtOp = createExtendInst(Op, WideType, Cmp->isSigned(), Cmp);
|
|
DU.NarrowUse->replaceUsesOfWith(Op, ExtOp);
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// Determine whether an individual user of the narrow IV can be widened. If so,
|
|
/// return the wide clone of the user.
|
|
Instruction *WidenIV::widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
|
|
|
|
// Stop traversing the def-use chain at inner-loop phis or post-loop phis.
|
|
if (PHINode *UsePhi = dyn_cast<PHINode>(DU.NarrowUse)) {
|
|
if (LI->getLoopFor(UsePhi->getParent()) != L) {
|
|
// For LCSSA phis, sink the truncate outside the loop.
|
|
// After SimplifyCFG most loop exit targets have a single predecessor.
|
|
// Otherwise fall back to a truncate within the loop.
|
|
if (UsePhi->getNumOperands() != 1)
|
|
truncateIVUse(DU, DT, LI);
|
|
else {
|
|
PHINode *WidePhi =
|
|
PHINode::Create(DU.WideDef->getType(), 1, UsePhi->getName() + ".wide",
|
|
UsePhi);
|
|
WidePhi->addIncoming(DU.WideDef, UsePhi->getIncomingBlock(0));
|
|
IRBuilder<> Builder(&*WidePhi->getParent()->getFirstInsertionPt());
|
|
Value *Trunc = Builder.CreateTrunc(WidePhi, DU.NarrowDef->getType());
|
|
UsePhi->replaceAllUsesWith(Trunc);
|
|
DeadInsts.emplace_back(UsePhi);
|
|
DEBUG(dbgs() << "INDVARS: Widen lcssa phi " << *UsePhi
|
|
<< " to " << *WidePhi << "\n");
|
|
}
|
|
return nullptr;
|
|
}
|
|
}
|
|
// Our raison d'etre! Eliminate sign and zero extension.
|
|
if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) {
|
|
Value *NewDef = DU.WideDef;
|
|
if (DU.NarrowUse->getType() != WideType) {
|
|
unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType());
|
|
unsigned IVWidth = SE->getTypeSizeInBits(WideType);
|
|
if (CastWidth < IVWidth) {
|
|
// The cast isn't as wide as the IV, so insert a Trunc.
|
|
IRBuilder<> Builder(DU.NarrowUse);
|
|
NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType());
|
|
}
|
|
else {
|
|
// A wider extend was hidden behind a narrower one. This may induce
|
|
// another round of IV widening in which the intermediate IV becomes
|
|
// dead. It should be very rare.
|
|
DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi
|
|
<< " not wide enough to subsume " << *DU.NarrowUse << "\n");
|
|
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
|
|
NewDef = DU.NarrowUse;
|
|
}
|
|
}
|
|
if (NewDef != DU.NarrowUse) {
|
|
DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse
|
|
<< " replaced by " << *DU.WideDef << "\n");
|
|
++NumElimExt;
|
|
DU.NarrowUse->replaceAllUsesWith(NewDef);
|
|
DeadInsts.emplace_back(DU.NarrowUse);
|
|
}
|
|
// Now that the extend is gone, we want to expose it's uses for potential
|
|
// further simplification. We don't need to directly inform SimplifyIVUsers
|
|
// of the new users, because their parent IV will be processed later as a
|
|
// new loop phi. If we preserved IVUsers analysis, we would also want to
|
|
// push the uses of WideDef here.
|
|
|
|
// No further widening is needed. The deceased [sz]ext had done it for us.
|
|
return nullptr;
|
|
}
|
|
|
|
// Does this user itself evaluate to a recurrence after widening?
|
|
const SCEVAddRecExpr *WideAddRec = getWideRecurrence(DU.NarrowUse);
|
|
if (!WideAddRec)
|
|
WideAddRec = getExtendedOperandRecurrence(DU);
|
|
|
|
if (!WideAddRec) {
|
|
// If use is a loop condition, try to promote the condition instead of
|
|
// truncating the IV first.
|
|
if (widenLoopCompare(DU))
|
|
return nullptr;
|
|
|
|
// This user does not evaluate to a recurence after widening, so don't
|
|
// follow it. Instead insert a Trunc to kill off the original use,
|
|
// eventually isolating the original narrow IV so it can be removed.
|
|
truncateIVUse(DU, DT, LI);
|
|
return nullptr;
|
|
}
|
|
// Assume block terminators cannot evaluate to a recurrence. We can't to
|
|
// insert a Trunc after a terminator if there happens to be a critical edge.
|
|
assert(DU.NarrowUse != DU.NarrowUse->getParent()->getTerminator() &&
|
|
"SCEV is not expected to evaluate a block terminator");
|
|
|
|
// Reuse the IV increment that SCEVExpander created as long as it dominates
|
|
// NarrowUse.
|
|
Instruction *WideUse = nullptr;
|
|
if (WideAddRec == WideIncExpr
|
|
&& Rewriter.hoistIVInc(WideInc, DU.NarrowUse))
|
|
WideUse = WideInc;
|
|
else {
|
|
WideUse = cloneIVUser(DU, WideAddRec);
|
|
if (!WideUse)
|
|
return nullptr;
|
|
}
|
|
// Evaluation of WideAddRec ensured that the narrow expression could be
|
|
// extended outside the loop without overflow. This suggests that the wide use
|
|
// evaluates to the same expression as the extended narrow use, but doesn't
|
|
// absolutely guarantee it. Hence the following failsafe check. In rare cases
|
|
// where it fails, we simply throw away the newly created wide use.
|
|
if (WideAddRec != SE->getSCEV(WideUse)) {
|
|
DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse
|
|
<< ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n");
|
|
DeadInsts.emplace_back(WideUse);
|
|
return nullptr;
|
|
}
|
|
|
|
// Returning WideUse pushes it on the worklist.
|
|
return WideUse;
|
|
}
|
|
|
|
/// Add eligible users of NarrowDef to NarrowIVUsers.
|
|
///
|
|
void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
|
|
const SCEV *NarrowSCEV = SE->getSCEV(NarrowDef);
|
|
bool NeverNegative =
|
|
SE->isKnownPredicate(ICmpInst::ICMP_SGE, NarrowSCEV,
|
|
SE->getConstant(NarrowSCEV->getType(), 0));
|
|
for (User *U : NarrowDef->users()) {
|
|
Instruction *NarrowUser = cast<Instruction>(U);
|
|
|
|
// Handle data flow merges and bizarre phi cycles.
|
|
if (!Widened.insert(NarrowUser).second)
|
|
continue;
|
|
|
|
NarrowIVUsers.push_back(
|
|
NarrowIVDefUse(NarrowDef, NarrowUser, WideDef, NeverNegative));
|
|
}
|
|
}
|
|
|
|
/// Process a single induction variable. First use the SCEVExpander to create a
|
|
/// wide induction variable that evaluates to the same recurrence as the
|
|
/// original narrow IV. Then use a worklist to forward traverse the narrow IV's
|
|
/// def-use chain. After widenIVUse has processed all interesting IV users, the
|
|
/// narrow IV will be isolated for removal by DeleteDeadPHIs.
|
|
///
|
|
/// It would be simpler to delete uses as they are processed, but we must avoid
|
|
/// invalidating SCEV expressions.
|
|
///
|
|
PHINode *WidenIV::createWideIV(SCEVExpander &Rewriter) {
|
|
// Is this phi an induction variable?
|
|
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
|
|
if (!AddRec)
|
|
return nullptr;
|
|
|
|
// Widen the induction variable expression.
|
|
const SCEV *WideIVExpr = IsSigned ?
|
|
SE->getSignExtendExpr(AddRec, WideType) :
|
|
SE->getZeroExtendExpr(AddRec, WideType);
|
|
|
|
assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType &&
|
|
"Expect the new IV expression to preserve its type");
|
|
|
|
// Can the IV be extended outside the loop without overflow?
|
|
AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
|
|
if (!AddRec || AddRec->getLoop() != L)
|
|
return nullptr;
|
|
|
|
// An AddRec must have loop-invariant operands. Since this AddRec is
|
|
// materialized by a loop header phi, the expression cannot have any post-loop
|
|
// operands, so they must dominate the loop header.
|
|
assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) &&
|
|
SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader())
|
|
&& "Loop header phi recurrence inputs do not dominate the loop");
|
|
|
|
// The rewriter provides a value for the desired IV expression. This may
|
|
// either find an existing phi or materialize a new one. Either way, we
|
|
// expect a well-formed cyclic phi-with-increments. i.e. any operand not part
|
|
// of the phi-SCC dominates the loop entry.
|
|
Instruction *InsertPt = &L->getHeader()->front();
|
|
WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
|
|
|
|
// Remembering the WideIV increment generated by SCEVExpander allows
|
|
// widenIVUse to reuse it when widening the narrow IV's increment. We don't
|
|
// employ a general reuse mechanism because the call above is the only call to
|
|
// SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses.
|
|
if (BasicBlock *LatchBlock = L->getLoopLatch()) {
|
|
WideInc =
|
|
cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
|
|
WideIncExpr = SE->getSCEV(WideInc);
|
|
}
|
|
|
|
DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
|
|
++NumWidened;
|
|
|
|
// Traverse the def-use chain using a worklist starting at the original IV.
|
|
assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" );
|
|
|
|
Widened.insert(OrigPhi);
|
|
pushNarrowIVUsers(OrigPhi, WidePhi);
|
|
|
|
while (!NarrowIVUsers.empty()) {
|
|
NarrowIVDefUse DU = NarrowIVUsers.pop_back_val();
|
|
|
|
// Process a def-use edge. This may replace the use, so don't hold a
|
|
// use_iterator across it.
|
|
Instruction *WideUse = widenIVUse(DU, Rewriter);
|
|
|
|
// Follow all def-use edges from the previous narrow use.
|
|
if (WideUse)
|
|
pushNarrowIVUsers(DU.NarrowUse, WideUse);
|
|
|
|
// widenIVUse may have removed the def-use edge.
|
|
if (DU.NarrowDef->use_empty())
|
|
DeadInsts.emplace_back(DU.NarrowDef);
|
|
}
|
|
return WidePhi;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// Live IV Reduction - Minimize IVs live across the loop.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// Simplification of IV users based on SCEV evaluation.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
namespace {
|
|
class IndVarSimplifyVisitor : public IVVisitor {
|
|
ScalarEvolution *SE;
|
|
const TargetTransformInfo *TTI;
|
|
PHINode *IVPhi;
|
|
|
|
public:
|
|
WideIVInfo WI;
|
|
|
|
IndVarSimplifyVisitor(PHINode *IV, ScalarEvolution *SCEV,
|
|
const TargetTransformInfo *TTI,
|
|
const DominatorTree *DTree)
|
|
: SE(SCEV), TTI(TTI), IVPhi(IV) {
|
|
DT = DTree;
|
|
WI.NarrowIV = IVPhi;
|
|
if (ReduceLiveIVs)
|
|
setSplitOverflowIntrinsics();
|
|
}
|
|
|
|
// Implement the interface used by simplifyUsersOfIV.
|
|
void visitCast(CastInst *Cast) override { visitIVCast(Cast, WI, SE, TTI); }
|
|
};
|
|
}
|
|
|
|
/// Iteratively perform simplification on a worklist of IV users. Each
|
|
/// successive simplification may push more users which may themselves be
|
|
/// candidates for simplification.
|
|
///
|
|
/// Sign/Zero extend elimination is interleaved with IV simplification.
|
|
///
|
|
void IndVarSimplify::simplifyAndExtend(Loop *L,
|
|
SCEVExpander &Rewriter,
|
|
LPPassManager &LPM) {
|
|
SmallVector<WideIVInfo, 8> WideIVs;
|
|
|
|
SmallVector<PHINode*, 8> LoopPhis;
|
|
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
|
|
LoopPhis.push_back(cast<PHINode>(I));
|
|
}
|
|
// Each round of simplification iterates through the SimplifyIVUsers worklist
|
|
// for all current phis, then determines whether any IVs can be
|
|
// widened. Widening adds new phis to LoopPhis, inducing another round of
|
|
// simplification on the wide IVs.
|
|
while (!LoopPhis.empty()) {
|
|
// Evaluate as many IV expressions as possible before widening any IVs. This
|
|
// forces SCEV to set no-wrap flags before evaluating sign/zero
|
|
// extension. The first time SCEV attempts to normalize sign/zero extension,
|
|
// the result becomes final. So for the most predictable results, we delay
|
|
// evaluation of sign/zero extend evaluation until needed, and avoid running
|
|
// other SCEV based analysis prior to simplifyAndExtend.
|
|
do {
|
|
PHINode *CurrIV = LoopPhis.pop_back_val();
|
|
|
|
// Information about sign/zero extensions of CurrIV.
|
|
IndVarSimplifyVisitor Visitor(CurrIV, SE, TTI, DT);
|
|
|
|
Changed |= simplifyUsersOfIV(CurrIV, SE, DT, &LPM, DeadInsts, &Visitor);
|
|
|
|
if (Visitor.WI.WidestNativeType) {
|
|
WideIVs.push_back(Visitor.WI);
|
|
}
|
|
} while(!LoopPhis.empty());
|
|
|
|
for (; !WideIVs.empty(); WideIVs.pop_back()) {
|
|
WidenIV Widener(WideIVs.back(), LI, SE, DT, DeadInsts);
|
|
if (PHINode *WidePhi = Widener.createWideIV(Rewriter)) {
|
|
Changed = true;
|
|
LoopPhis.push_back(WidePhi);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// linearFunctionTestReplace and its kin. Rewrite the loop exit condition.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// Return true if this loop's backedge taken count expression can be safely and
|
|
/// cheaply expanded into an instruction sequence that can be used by
|
|
/// linearFunctionTestReplace.
|
|
///
|
|
/// TODO: This fails for pointer-type loop counters with greater than one byte
|
|
/// strides, consequently preventing LFTR from running. For the purpose of LFTR
|
|
/// we could skip this check in the case that the LFTR loop counter (chosen by
|
|
/// FindLoopCounter) is also pointer type. Instead, we could directly convert
|
|
/// the loop test to an inequality test by checking the target data's alignment
|
|
/// of element types (given that the initial pointer value originates from or is
|
|
/// used by ABI constrained operation, as opposed to inttoptr/ptrtoint).
|
|
/// However, we don't yet have a strong motivation for converting loop tests
|
|
/// into inequality tests.
|
|
static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE,
|
|
SCEVExpander &Rewriter) {
|
|
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) ||
|
|
BackedgeTakenCount->isZero())
|
|
return false;
|
|
|
|
if (!L->getExitingBlock())
|
|
return false;
|
|
|
|
// Can't rewrite non-branch yet.
|
|
if (!isa<BranchInst>(L->getExitingBlock()->getTerminator()))
|
|
return false;
|
|
|
|
if (Rewriter.isHighCostExpansion(BackedgeTakenCount, L))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Return the loop header phi IFF IncV adds a loop invariant value to the phi.
|
|
static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) {
|
|
Instruction *IncI = dyn_cast<Instruction>(IncV);
|
|
if (!IncI)
|
|
return nullptr;
|
|
|
|
switch (IncI->getOpcode()) {
|
|
case Instruction::Add:
|
|
case Instruction::Sub:
|
|
break;
|
|
case Instruction::GetElementPtr:
|
|
// An IV counter must preserve its type.
|
|
if (IncI->getNumOperands() == 2)
|
|
break;
|
|
default:
|
|
return nullptr;
|
|
}
|
|
|
|
PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0));
|
|
if (Phi && Phi->getParent() == L->getHeader()) {
|
|
if (isLoopInvariant(IncI->getOperand(1), L, DT))
|
|
return Phi;
|
|
return nullptr;
|
|
}
|
|
if (IncI->getOpcode() == Instruction::GetElementPtr)
|
|
return nullptr;
|
|
|
|
// Allow add/sub to be commuted.
|
|
Phi = dyn_cast<PHINode>(IncI->getOperand(1));
|
|
if (Phi && Phi->getParent() == L->getHeader()) {
|
|
if (isLoopInvariant(IncI->getOperand(0), L, DT))
|
|
return Phi;
|
|
}
|
|
return nullptr;
|
|
}
|
|
|
|
/// Return the compare guarding the loop latch, or NULL for unrecognized tests.
|
|
static ICmpInst *getLoopTest(Loop *L) {
|
|
assert(L->getExitingBlock() && "expected loop exit");
|
|
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
// Don't bother with LFTR if the loop is not properly simplified.
|
|
if (!LatchBlock)
|
|
return nullptr;
|
|
|
|
BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
assert(BI && "expected exit branch");
|
|
|
|
return dyn_cast<ICmpInst>(BI->getCondition());
|
|
}
|
|
|
|
/// linearFunctionTestReplace policy. Return true unless we can show that the
|
|
/// current exit test is already sufficiently canonical.
|
|
static bool needsLFTR(Loop *L, DominatorTree *DT) {
|
|
// Do LFTR to simplify the exit condition to an ICMP.
|
|
ICmpInst *Cond = getLoopTest(L);
|
|
if (!Cond)
|
|
return true;
|
|
|
|
// Do LFTR to simplify the exit ICMP to EQ/NE
|
|
ICmpInst::Predicate Pred = Cond->getPredicate();
|
|
if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ)
|
|
return true;
|
|
|
|
// Look for a loop invariant RHS
|
|
Value *LHS = Cond->getOperand(0);
|
|
Value *RHS = Cond->getOperand(1);
|
|
if (!isLoopInvariant(RHS, L, DT)) {
|
|
if (!isLoopInvariant(LHS, L, DT))
|
|
return true;
|
|
std::swap(LHS, RHS);
|
|
}
|
|
// Look for a simple IV counter LHS
|
|
PHINode *Phi = dyn_cast<PHINode>(LHS);
|
|
if (!Phi)
|
|
Phi = getLoopPhiForCounter(LHS, L, DT);
|
|
|
|
if (!Phi)
|
|
return true;
|
|
|
|
// Do LFTR if PHI node is defined in the loop, but is *not* a counter.
|
|
int Idx = Phi->getBasicBlockIndex(L->getLoopLatch());
|
|
if (Idx < 0)
|
|
return true;
|
|
|
|
// Do LFTR if the exit condition's IV is *not* a simple counter.
|
|
Value *IncV = Phi->getIncomingValue(Idx);
|
|
return Phi != getLoopPhiForCounter(IncV, L, DT);
|
|
}
|
|
|
|
/// Recursive helper for hasConcreteDef(). Unfortunately, this currently boils
|
|
/// down to checking that all operands are constant and listing instructions
|
|
/// that may hide undef.
|
|
static bool hasConcreteDefImpl(Value *V, SmallPtrSetImpl<Value*> &Visited,
|
|
unsigned Depth) {
|
|
if (isa<Constant>(V))
|
|
return !isa<UndefValue>(V);
|
|
|
|
if (Depth >= 6)
|
|
return false;
|
|
|
|
// Conservatively handle non-constant non-instructions. For example, Arguments
|
|
// may be undef.
|
|
Instruction *I = dyn_cast<Instruction>(V);
|
|
if (!I)
|
|
return false;
|
|
|
|
// Load and return values may be undef.
|
|
if(I->mayReadFromMemory() || isa<CallInst>(I) || isa<InvokeInst>(I))
|
|
return false;
|
|
|
|
// Optimistically handle other instructions.
|
|
for (Value *Op : I->operands()) {
|
|
if (!Visited.insert(Op).second)
|
|
continue;
|
|
if (!hasConcreteDefImpl(Op, Visited, Depth+1))
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// Return true if the given value is concrete. We must prove that undef can
|
|
/// never reach it.
|
|
///
|
|
/// TODO: If we decide that this is a good approach to checking for undef, we
|
|
/// may factor it into a common location.
|
|
static bool hasConcreteDef(Value *V) {
|
|
SmallPtrSet<Value*, 8> Visited;
|
|
Visited.insert(V);
|
|
return hasConcreteDefImpl(V, Visited, 0);
|
|
}
|
|
|
|
/// Return true if this IV has any uses other than the (soon to be rewritten)
|
|
/// loop exit test.
|
|
static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) {
|
|
int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
|
|
Value *IncV = Phi->getIncomingValue(LatchIdx);
|
|
|
|
for (User *U : Phi->users())
|
|
if (U != Cond && U != IncV) return false;
|
|
|
|
for (User *U : IncV->users())
|
|
if (U != Cond && U != Phi) return false;
|
|
return true;
|
|
}
|
|
|
|
/// Find an affine IV in canonical form.
|
|
///
|
|
/// BECount may be an i8* pointer type. The pointer difference is already
|
|
/// valid count without scaling the address stride, so it remains a pointer
|
|
/// expression as far as SCEV is concerned.
|
|
///
|
|
/// Currently only valid for LFTR. See the comments on hasConcreteDef below.
|
|
///
|
|
/// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount
|
|
///
|
|
/// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride.
|
|
/// This is difficult in general for SCEV because of potential overflow. But we
|
|
/// could at least handle constant BECounts.
|
|
static PHINode *FindLoopCounter(Loop *L, const SCEV *BECount,
|
|
ScalarEvolution *SE, DominatorTree *DT) {
|
|
uint64_t BCWidth = SE->getTypeSizeInBits(BECount->getType());
|
|
|
|
Value *Cond =
|
|
cast<BranchInst>(L->getExitingBlock()->getTerminator())->getCondition();
|
|
|
|
// Loop over all of the PHI nodes, looking for a simple counter.
|
|
PHINode *BestPhi = nullptr;
|
|
const SCEV *BestInit = nullptr;
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
assert(LatchBlock && "needsLFTR should guarantee a loop latch");
|
|
|
|
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *Phi = cast<PHINode>(I);
|
|
if (!SE->isSCEVable(Phi->getType()))
|
|
continue;
|
|
|
|
// Avoid comparing an integer IV against a pointer Limit.
|
|
if (BECount->getType()->isPointerTy() && !Phi->getType()->isPointerTy())
|
|
continue;
|
|
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi));
|
|
if (!AR || AR->getLoop() != L || !AR->isAffine())
|
|
continue;
|
|
|
|
// AR may be a pointer type, while BECount is an integer type.
|
|
// AR may be wider than BECount. With eq/ne tests overflow is immaterial.
|
|
// AR may not be a narrower type, or we may never exit.
|
|
uint64_t PhiWidth = SE->getTypeSizeInBits(AR->getType());
|
|
if (PhiWidth < BCWidth ||
|
|
!L->getHeader()->getModule()->getDataLayout().isLegalInteger(PhiWidth))
|
|
continue;
|
|
|
|
const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
|
|
if (!Step || !Step->isOne())
|
|
continue;
|
|
|
|
int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
|
|
Value *IncV = Phi->getIncomingValue(LatchIdx);
|
|
if (getLoopPhiForCounter(IncV, L, DT) != Phi)
|
|
continue;
|
|
|
|
// Avoid reusing a potentially undef value to compute other values that may
|
|
// have originally had a concrete definition.
|
|
if (!hasConcreteDef(Phi)) {
|
|
// We explicitly allow unknown phis as long as they are already used by
|
|
// the loop test. In this case we assume that performing LFTR could not
|
|
// increase the number of undef users.
|
|
if (ICmpInst *Cond = getLoopTest(L)) {
|
|
if (Phi != getLoopPhiForCounter(Cond->getOperand(0), L, DT)
|
|
&& Phi != getLoopPhiForCounter(Cond->getOperand(1), L, DT)) {
|
|
continue;
|
|
}
|
|
}
|
|
}
|
|
const SCEV *Init = AR->getStart();
|
|
|
|
if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) {
|
|
// Don't force a live loop counter if another IV can be used.
|
|
if (AlmostDeadIV(Phi, LatchBlock, Cond))
|
|
continue;
|
|
|
|
// Prefer to count-from-zero. This is a more "canonical" counter form. It
|
|
// also prefers integer to pointer IVs.
|
|
if (BestInit->isZero() != Init->isZero()) {
|
|
if (BestInit->isZero())
|
|
continue;
|
|
}
|
|
// If two IVs both count from zero or both count from nonzero then the
|
|
// narrower is likely a dead phi that has been widened. Use the wider phi
|
|
// to allow the other to be eliminated.
|
|
else if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType()))
|
|
continue;
|
|
}
|
|
BestPhi = Phi;
|
|
BestInit = Init;
|
|
}
|
|
return BestPhi;
|
|
}
|
|
|
|
/// Help linearFunctionTestReplace by generating a value that holds the RHS of
|
|
/// the new loop test.
|
|
static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L,
|
|
SCEVExpander &Rewriter, ScalarEvolution *SE) {
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
|
|
assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter");
|
|
const SCEV *IVInit = AR->getStart();
|
|
|
|
// IVInit may be a pointer while IVCount is an integer when FindLoopCounter
|
|
// finds a valid pointer IV. Sign extend BECount in order to materialize a
|
|
// GEP. Avoid running SCEVExpander on a new pointer value, instead reusing
|
|
// the existing GEPs whenever possible.
|
|
if (IndVar->getType()->isPointerTy()
|
|
&& !IVCount->getType()->isPointerTy()) {
|
|
|
|
// IVOffset will be the new GEP offset that is interpreted by GEP as a
|
|
// signed value. IVCount on the other hand represents the loop trip count,
|
|
// which is an unsigned value. FindLoopCounter only allows induction
|
|
// variables that have a positive unit stride of one. This means we don't
|
|
// have to handle the case of negative offsets (yet) and just need to zero
|
|
// extend IVCount.
|
|
Type *OfsTy = SE->getEffectiveSCEVType(IVInit->getType());
|
|
const SCEV *IVOffset = SE->getTruncateOrZeroExtend(IVCount, OfsTy);
|
|
|
|
// Expand the code for the iteration count.
|
|
assert(SE->isLoopInvariant(IVOffset, L) &&
|
|
"Computed iteration count is not loop invariant!");
|
|
BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
Value *GEPOffset = Rewriter.expandCodeFor(IVOffset, OfsTy, BI);
|
|
|
|
Value *GEPBase = IndVar->getIncomingValueForBlock(L->getLoopPreheader());
|
|
assert(AR->getStart() == SE->getSCEV(GEPBase) && "bad loop counter");
|
|
// We could handle pointer IVs other than i8*, but we need to compensate for
|
|
// gep index scaling. See canExpandBackedgeTakenCount comments.
|
|
assert(SE->getSizeOfExpr(IntegerType::getInt64Ty(IndVar->getContext()),
|
|
cast<PointerType>(GEPBase->getType())->getElementType())->isOne()
|
|
&& "unit stride pointer IV must be i8*");
|
|
|
|
IRBuilder<> Builder(L->getLoopPreheader()->getTerminator());
|
|
return Builder.CreateGEP(nullptr, GEPBase, GEPOffset, "lftr.limit");
|
|
}
|
|
else {
|
|
// In any other case, convert both IVInit and IVCount to integers before
|
|
// comparing. This may result in SCEV expension of pointers, but in practice
|
|
// SCEV will fold the pointer arithmetic away as such:
|
|
// BECount = (IVEnd - IVInit - 1) => IVLimit = IVInit (postinc).
|
|
//
|
|
// Valid Cases: (1) both integers is most common; (2) both may be pointers
|
|
// for simple memset-style loops.
|
|
//
|
|
// IVInit integer and IVCount pointer would only occur if a canonical IV
|
|
// were generated on top of case #2, which is not expected.
|
|
|
|
const SCEV *IVLimit = nullptr;
|
|
// For unit stride, IVCount = Start + BECount with 2's complement overflow.
|
|
// For non-zero Start, compute IVCount here.
|
|
if (AR->getStart()->isZero())
|
|
IVLimit = IVCount;
|
|
else {
|
|
assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride");
|
|
const SCEV *IVInit = AR->getStart();
|
|
|
|
// For integer IVs, truncate the IV before computing IVInit + BECount.
|
|
if (SE->getTypeSizeInBits(IVInit->getType())
|
|
> SE->getTypeSizeInBits(IVCount->getType()))
|
|
IVInit = SE->getTruncateExpr(IVInit, IVCount->getType());
|
|
|
|
IVLimit = SE->getAddExpr(IVInit, IVCount);
|
|
}
|
|
// Expand the code for the iteration count.
|
|
BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
IRBuilder<> Builder(BI);
|
|
assert(SE->isLoopInvariant(IVLimit, L) &&
|
|
"Computed iteration count is not loop invariant!");
|
|
// Ensure that we generate the same type as IndVar, or a smaller integer
|
|
// type. In the presence of null pointer values, we have an integer type
|
|
// SCEV expression (IVInit) for a pointer type IV value (IndVar).
|
|
Type *LimitTy = IVCount->getType()->isPointerTy() ?
|
|
IndVar->getType() : IVCount->getType();
|
|
return Rewriter.expandCodeFor(IVLimit, LimitTy, BI);
|
|
}
|
|
}
|
|
|
|
/// This method rewrites the exit condition of the loop to be a canonical !=
|
|
/// comparison against the incremented loop induction variable. This pass is
|
|
/// able to rewrite the exit tests of any loop where the SCEV analysis can
|
|
/// determine a loop-invariant trip count of the loop, which is actually a much
|
|
/// broader range than just linear tests.
|
|
Value *IndVarSimplify::
|
|
linearFunctionTestReplace(Loop *L,
|
|
const SCEV *BackedgeTakenCount,
|
|
PHINode *IndVar,
|
|
SCEVExpander &Rewriter) {
|
|
assert(canExpandBackedgeTakenCount(L, SE, Rewriter) && "precondition");
|
|
|
|
// Initialize CmpIndVar and IVCount to their preincremented values.
|
|
Value *CmpIndVar = IndVar;
|
|
const SCEV *IVCount = BackedgeTakenCount;
|
|
|
|
// If the exiting block is the same as the backedge block, we prefer to
|
|
// compare against the post-incremented value, otherwise we must compare
|
|
// against the preincremented value.
|
|
if (L->getExitingBlock() == L->getLoopLatch()) {
|
|
// Add one to the "backedge-taken" count to get the trip count.
|
|
// This addition may overflow, which is valid as long as the comparison is
|
|
// truncated to BackedgeTakenCount->getType().
|
|
IVCount = SE->getAddExpr(BackedgeTakenCount,
|
|
SE->getOne(BackedgeTakenCount->getType()));
|
|
// The BackedgeTaken expression contains the number of times that the
|
|
// backedge branches to the loop header. This is one less than the
|
|
// number of times the loop executes, so use the incremented indvar.
|
|
CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
|
|
}
|
|
|
|
Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE);
|
|
assert(ExitCnt->getType()->isPointerTy() == IndVar->getType()->isPointerTy()
|
|
&& "genLoopLimit missed a cast");
|
|
|
|
// Insert a new icmp_ne or icmp_eq instruction before the branch.
|
|
BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
|
|
ICmpInst::Predicate P;
|
|
if (L->contains(BI->getSuccessor(0)))
|
|
P = ICmpInst::ICMP_NE;
|
|
else
|
|
P = ICmpInst::ICMP_EQ;
|
|
|
|
DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
|
|
<< " LHS:" << *CmpIndVar << '\n'
|
|
<< " op:\t"
|
|
<< (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
|
|
<< " RHS:\t" << *ExitCnt << "\n"
|
|
<< " IVCount:\t" << *IVCount << "\n");
|
|
|
|
IRBuilder<> Builder(BI);
|
|
|
|
// LFTR can ignore IV overflow and truncate to the width of
|
|
// BECount. This avoids materializing the add(zext(add)) expression.
|
|
unsigned CmpIndVarSize = SE->getTypeSizeInBits(CmpIndVar->getType());
|
|
unsigned ExitCntSize = SE->getTypeSizeInBits(ExitCnt->getType());
|
|
if (CmpIndVarSize > ExitCntSize) {
|
|
const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
|
|
const SCEV *ARStart = AR->getStart();
|
|
const SCEV *ARStep = AR->getStepRecurrence(*SE);
|
|
// For constant IVCount, avoid truncation.
|
|
if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) {
|
|
const APInt &Start = cast<SCEVConstant>(ARStart)->getValue()->getValue();
|
|
APInt Count = cast<SCEVConstant>(IVCount)->getValue()->getValue();
|
|
// Note that the post-inc value of BackedgeTakenCount may have overflowed
|
|
// above such that IVCount is now zero.
|
|
if (IVCount != BackedgeTakenCount && Count == 0) {
|
|
Count = APInt::getMaxValue(Count.getBitWidth()).zext(CmpIndVarSize);
|
|
++Count;
|
|
}
|
|
else
|
|
Count = Count.zext(CmpIndVarSize);
|
|
APInt NewLimit;
|
|
if (cast<SCEVConstant>(ARStep)->getValue()->isNegative())
|
|
NewLimit = Start - Count;
|
|
else
|
|
NewLimit = Start + Count;
|
|
ExitCnt = ConstantInt::get(CmpIndVar->getType(), NewLimit);
|
|
|
|
DEBUG(dbgs() << " Widen RHS:\t" << *ExitCnt << "\n");
|
|
} else {
|
|
CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
|
|
"lftr.wideiv");
|
|
}
|
|
}
|
|
Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");
|
|
Value *OrigCond = BI->getCondition();
|
|
// It's tempting to use replaceAllUsesWith here to fully replace the old
|
|
// comparison, but that's not immediately safe, since users of the old
|
|
// comparison may not be dominated by the new comparison. Instead, just
|
|
// update the branch to use the new comparison; in the common case this
|
|
// will make old comparison dead.
|
|
BI->setCondition(Cond);
|
|
DeadInsts.push_back(OrigCond);
|
|
|
|
++NumLFTR;
|
|
Changed = true;
|
|
return Cond;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// sinkUnusedInvariants. A late subpass to cleanup loop preheaders.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// If there's a single exit block, sink any loop-invariant values that
|
|
/// were defined in the preheader but not used inside the loop into the
|
|
/// exit block to reduce register pressure in the loop.
|
|
void IndVarSimplify::sinkUnusedInvariants(Loop *L) {
|
|
BasicBlock *ExitBlock = L->getExitBlock();
|
|
if (!ExitBlock) return;
|
|
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
if (!Preheader) return;
|
|
|
|
Instruction *InsertPt = &*ExitBlock->getFirstInsertionPt();
|
|
BasicBlock::iterator I(Preheader->getTerminator());
|
|
while (I != Preheader->begin()) {
|
|
--I;
|
|
// New instructions were inserted at the end of the preheader.
|
|
if (isa<PHINode>(I))
|
|
break;
|
|
|
|
// Don't move instructions which might have side effects, since the side
|
|
// effects need to complete before instructions inside the loop. Also don't
|
|
// move instructions which might read memory, since the loop may modify
|
|
// memory. Note that it's okay if the instruction might have undefined
|
|
// behavior: LoopSimplify guarantees that the preheader dominates the exit
|
|
// block.
|
|
if (I->mayHaveSideEffects() || I->mayReadFromMemory())
|
|
continue;
|
|
|
|
// Skip debug info intrinsics.
|
|
if (isa<DbgInfoIntrinsic>(I))
|
|
continue;
|
|
|
|
// Skip eh pad instructions.
|
|
if (I->isEHPad())
|
|
continue;
|
|
|
|
// Don't sink alloca: we never want to sink static alloca's out of the
|
|
// entry block, and correctly sinking dynamic alloca's requires
|
|
// checks for stacksave/stackrestore intrinsics.
|
|
// FIXME: Refactor this check somehow?
|
|
if (isa<AllocaInst>(I))
|
|
continue;
|
|
|
|
// Determine if there is a use in or before the loop (direct or
|
|
// otherwise).
|
|
bool UsedInLoop = false;
|
|
for (Use &U : I->uses()) {
|
|
Instruction *User = cast<Instruction>(U.getUser());
|
|
BasicBlock *UseBB = User->getParent();
|
|
if (PHINode *P = dyn_cast<PHINode>(User)) {
|
|
unsigned i =
|
|
PHINode::getIncomingValueNumForOperand(U.getOperandNo());
|
|
UseBB = P->getIncomingBlock(i);
|
|
}
|
|
if (UseBB == Preheader || L->contains(UseBB)) {
|
|
UsedInLoop = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If there is, the def must remain in the preheader.
|
|
if (UsedInLoop)
|
|
continue;
|
|
|
|
// Otherwise, sink it to the exit block.
|
|
Instruction *ToMove = &*I;
|
|
bool Done = false;
|
|
|
|
if (I != Preheader->begin()) {
|
|
// Skip debug info intrinsics.
|
|
do {
|
|
--I;
|
|
} while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
|
|
|
|
if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
|
|
Done = true;
|
|
} else {
|
|
Done = true;
|
|
}
|
|
|
|
ToMove->moveBefore(InsertPt);
|
|
if (Done) break;
|
|
InsertPt = ToMove;
|
|
}
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// IndVarSimplify driver. Manage several subpasses of IV simplification.
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
if (skipOptnoneFunction(L))
|
|
return false;
|
|
|
|
// If LoopSimplify form is not available, stay out of trouble. Some notes:
|
|
// - LSR currently only supports LoopSimplify-form loops. Indvars'
|
|
// canonicalization can be a pessimization without LSR to "clean up"
|
|
// afterwards.
|
|
// - We depend on having a preheader; in particular,
|
|
// Loop::getCanonicalInductionVariable only supports loops with preheaders,
|
|
// and we're in trouble if we can't find the induction variable even when
|
|
// we've manually inserted one.
|
|
if (!L->isLoopSimplifyForm())
|
|
return false;
|
|
|
|
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
|
|
SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
|
|
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
|
|
TLI = TLIP ? &TLIP->getTLI() : nullptr;
|
|
auto *TTIP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
|
|
TTI = TTIP ? &TTIP->getTTI(*L->getHeader()->getParent()) : nullptr;
|
|
const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
|
|
|
|
DeadInsts.clear();
|
|
Changed = false;
|
|
|
|
// If there are any floating-point recurrences, attempt to
|
|
// transform them to use integer recurrences.
|
|
rewriteNonIntegerIVs(L);
|
|
|
|
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
|
|
|
|
// Create a rewriter object which we'll use to transform the code with.
|
|
SCEVExpander Rewriter(*SE, DL, "indvars");
|
|
#ifndef NDEBUG
|
|
Rewriter.setDebugType(DEBUG_TYPE);
|
|
#endif
|
|
|
|
// Eliminate redundant IV users.
|
|
//
|
|
// Simplification works best when run before other consumers of SCEV. We
|
|
// attempt to avoid evaluating SCEVs for sign/zero extend operations until
|
|
// other expressions involving loop IVs have been evaluated. This helps SCEV
|
|
// set no-wrap flags before normalizing sign/zero extension.
|
|
Rewriter.disableCanonicalMode();
|
|
simplifyAndExtend(L, Rewriter, LPM);
|
|
|
|
// Check to see if this loop has a computable loop-invariant execution count.
|
|
// If so, this means that we can compute the final value of any expressions
|
|
// that are recurrent in the loop, and substitute the exit values from the
|
|
// loop into any instructions outside of the loop that use the final values of
|
|
// the current expressions.
|
|
//
|
|
if (ReplaceExitValue != NeverRepl &&
|
|
!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
|
|
rewriteLoopExitValues(L, Rewriter);
|
|
|
|
// Eliminate redundant IV cycles.
|
|
NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts);
|
|
|
|
// If we have a trip count expression, rewrite the loop's exit condition
|
|
// using it. We can currently only handle loops with a single exit.
|
|
if (canExpandBackedgeTakenCount(L, SE, Rewriter) && needsLFTR(L, DT)) {
|
|
PHINode *IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT);
|
|
if (IndVar) {
|
|
// Check preconditions for proper SCEVExpander operation. SCEV does not
|
|
// express SCEVExpander's dependencies, such as LoopSimplify. Instead any
|
|
// pass that uses the SCEVExpander must do it. This does not work well for
|
|
// loop passes because SCEVExpander makes assumptions about all loops,
|
|
// while LoopPassManager only forces the current loop to be simplified.
|
|
//
|
|
// FIXME: SCEV expansion has no way to bail out, so the caller must
|
|
// explicitly check any assumptions made by SCEV. Brittle.
|
|
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BackedgeTakenCount);
|
|
if (!AR || AR->getLoop()->getLoopPreheader())
|
|
(void)linearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
|
|
Rewriter);
|
|
}
|
|
}
|
|
// Clear the rewriter cache, because values that are in the rewriter's cache
|
|
// can be deleted in the loop below, causing the AssertingVH in the cache to
|
|
// trigger.
|
|
Rewriter.clear();
|
|
|
|
// Now that we're done iterating through lists, clean up any instructions
|
|
// which are now dead.
|
|
while (!DeadInsts.empty())
|
|
if (Instruction *Inst =
|
|
dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
|
|
RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
|
|
|
|
// The Rewriter may not be used from this point on.
|
|
|
|
// Loop-invariant instructions in the preheader that aren't used in the
|
|
// loop may be sunk below the loop to reduce register pressure.
|
|
sinkUnusedInvariants(L);
|
|
|
|
// Clean up dead instructions.
|
|
Changed |= DeleteDeadPHIs(L->getHeader(), TLI);
|
|
|
|
// Check a post-condition.
|
|
assert(L->isRecursivelyLCSSAForm(*DT) && "Indvars did not preserve LCSSA!");
|
|
|
|
// Verify that LFTR, and any other change have not interfered with SCEV's
|
|
// ability to compute trip count.
|
|
#ifndef NDEBUG
|
|
if (VerifyIndvars && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
|
|
SE->forgetLoop(L);
|
|
const SCEV *NewBECount = SE->getBackedgeTakenCount(L);
|
|
if (SE->getTypeSizeInBits(BackedgeTakenCount->getType()) <
|
|
SE->getTypeSizeInBits(NewBECount->getType()))
|
|
NewBECount = SE->getTruncateOrNoop(NewBECount,
|
|
BackedgeTakenCount->getType());
|
|
else
|
|
BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount,
|
|
NewBECount->getType());
|
|
assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV");
|
|
}
|
|
#endif
|
|
|
|
return Changed;
|
|
}
|