forked from OSchip/llvm-project
582 lines
19 KiB
C++
582 lines
19 KiB
C++
//===- CorrelatedValuePropagation.cpp - Propagate CFG-derived info --------===//
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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 file implements the Correlated Value Propagation pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/CorrelatedValuePropagation.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LazyValueInfo.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/ConstantRange.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.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/Scalar.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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#define DEBUG_TYPE "correlated-value-propagation"
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STATISTIC(NumPhis, "Number of phis propagated");
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STATISTIC(NumSelects, "Number of selects propagated");
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STATISTIC(NumMemAccess, "Number of memory access targets propagated");
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STATISTIC(NumCmps, "Number of comparisons propagated");
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STATISTIC(NumReturns, "Number of return values propagated");
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STATISTIC(NumDeadCases, "Number of switch cases removed");
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STATISTIC(NumSDivs, "Number of sdiv converted to udiv");
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STATISTIC(NumAShrs, "Number of ashr converted to lshr");
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STATISTIC(NumSRems, "Number of srem converted to urem");
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static cl::opt<bool> DontProcessAdds("cvp-dont-process-adds", cl::init(true));
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namespace {
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class CorrelatedValuePropagation : public FunctionPass {
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public:
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static char ID;
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CorrelatedValuePropagation(): FunctionPass(ID) {
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initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<LazyValueInfoWrapperPass>();
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AU.addPreserved<GlobalsAAWrapperPass>();
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}
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};
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}
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char CorrelatedValuePropagation::ID = 0;
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INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
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"Value Propagation", false, false)
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INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)
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INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
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"Value Propagation", false, false)
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// Public interface to the Value Propagation pass
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Pass *llvm::createCorrelatedValuePropagationPass() {
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return new CorrelatedValuePropagation();
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}
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static bool processSelect(SelectInst *S, LazyValueInfo *LVI) {
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if (S->getType()->isVectorTy()) return false;
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if (isa<Constant>(S->getOperand(0))) return false;
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Constant *C = LVI->getConstant(S->getOperand(0), S->getParent(), S);
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if (!C) return false;
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ConstantInt *CI = dyn_cast<ConstantInt>(C);
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if (!CI) return false;
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Value *ReplaceWith = S->getOperand(1);
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Value *Other = S->getOperand(2);
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if (!CI->isOne()) std::swap(ReplaceWith, Other);
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if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType());
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S->replaceAllUsesWith(ReplaceWith);
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S->eraseFromParent();
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++NumSelects;
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return true;
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}
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static bool processPHI(PHINode *P, LazyValueInfo *LVI,
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const SimplifyQuery &SQ) {
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bool Changed = false;
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BasicBlock *BB = P->getParent();
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for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
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Value *Incoming = P->getIncomingValue(i);
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if (isa<Constant>(Incoming)) continue;
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Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB, P);
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// Look if the incoming value is a select with a scalar condition for which
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// LVI can tells us the value. In that case replace the incoming value with
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// the appropriate value of the select. This often allows us to remove the
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// select later.
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if (!V) {
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SelectInst *SI = dyn_cast<SelectInst>(Incoming);
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if (!SI) continue;
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Value *Condition = SI->getCondition();
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if (!Condition->getType()->isVectorTy()) {
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if (Constant *C = LVI->getConstantOnEdge(
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Condition, P->getIncomingBlock(i), BB, P)) {
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if (C->isOneValue()) {
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V = SI->getTrueValue();
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} else if (C->isZeroValue()) {
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V = SI->getFalseValue();
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}
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// Once LVI learns to handle vector types, we could also add support
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// for vector type constants that are not all zeroes or all ones.
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}
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}
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// Look if the select has a constant but LVI tells us that the incoming
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// value can never be that constant. In that case replace the incoming
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// value with the other value of the select. This often allows us to
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// remove the select later.
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if (!V) {
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Constant *C = dyn_cast<Constant>(SI->getFalseValue());
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if (!C) continue;
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if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
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P->getIncomingBlock(i), BB, P) !=
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LazyValueInfo::False)
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continue;
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V = SI->getTrueValue();
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}
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DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
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}
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P->setIncomingValue(i, V);
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Changed = true;
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}
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if (Value *V = SimplifyInstruction(P, SQ)) {
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P->replaceAllUsesWith(V);
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P->eraseFromParent();
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Changed = true;
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}
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if (Changed)
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++NumPhis;
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return Changed;
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}
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static bool processMemAccess(Instruction *I, LazyValueInfo *LVI) {
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Value *Pointer = nullptr;
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if (LoadInst *L = dyn_cast<LoadInst>(I))
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Pointer = L->getPointerOperand();
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else
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Pointer = cast<StoreInst>(I)->getPointerOperand();
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if (isa<Constant>(Pointer)) return false;
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Constant *C = LVI->getConstant(Pointer, I->getParent(), I);
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if (!C) return false;
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++NumMemAccess;
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I->replaceUsesOfWith(Pointer, C);
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return true;
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}
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/// See if LazyValueInfo's ability to exploit edge conditions or range
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/// information is sufficient to prove this comparison. Even for local
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/// conditions, this can sometimes prove conditions instcombine can't by
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/// exploiting range information.
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static bool processCmp(CmpInst *C, LazyValueInfo *LVI) {
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Value *Op0 = C->getOperand(0);
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Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
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if (!Op1) return false;
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// As a policy choice, we choose not to waste compile time on anything where
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// the comparison is testing local values. While LVI can sometimes reason
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// about such cases, it's not its primary purpose. We do make sure to do
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// the block local query for uses from terminator instructions, but that's
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// handled in the code for each terminator.
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auto *I = dyn_cast<Instruction>(Op0);
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if (I && I->getParent() == C->getParent())
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return false;
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LazyValueInfo::Tristate Result =
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LVI->getPredicateAt(C->getPredicate(), Op0, Op1, C);
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if (Result == LazyValueInfo::Unknown) return false;
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++NumCmps;
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if (Result == LazyValueInfo::True)
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C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
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else
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C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
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C->eraseFromParent();
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return true;
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}
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/// Simplify a switch instruction by removing cases which can never fire. If the
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/// uselessness of a case could be determined locally then constant propagation
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/// would already have figured it out. Instead, walk the predecessors and
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/// statically evaluate cases based on information available on that edge. Cases
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/// that cannot fire no matter what the incoming edge can safely be removed. If
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/// a case fires on every incoming edge then the entire switch can be removed
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/// and replaced with a branch to the case destination.
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static bool processSwitch(SwitchInst *SI, LazyValueInfo *LVI) {
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Value *Cond = SI->getCondition();
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BasicBlock *BB = SI->getParent();
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// If the condition was defined in same block as the switch then LazyValueInfo
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// currently won't say anything useful about it, though in theory it could.
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if (isa<Instruction>(Cond) && cast<Instruction>(Cond)->getParent() == BB)
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return false;
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// If the switch is unreachable then trying to improve it is a waste of time.
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pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
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if (PB == PE) return false;
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// Analyse each switch case in turn. This is done in reverse order so that
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// removing a case doesn't cause trouble for the iteration.
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bool Changed = false;
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for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
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ConstantInt *Case = CI->getCaseValue();
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// Check to see if the switch condition is equal to/not equal to the case
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// value on every incoming edge, equal/not equal being the same each time.
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LazyValueInfo::Tristate State = LazyValueInfo::Unknown;
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for (pred_iterator PI = PB; PI != PE; ++PI) {
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// Is the switch condition equal to the case value?
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LazyValueInfo::Tristate Value = LVI->getPredicateOnEdge(CmpInst::ICMP_EQ,
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Cond, Case, *PI,
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BB, SI);
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// Give up on this case if nothing is known.
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if (Value == LazyValueInfo::Unknown) {
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State = LazyValueInfo::Unknown;
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break;
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}
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// If this was the first edge to be visited, record that all other edges
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// need to give the same result.
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if (PI == PB) {
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State = Value;
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continue;
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}
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// If this case is known to fire for some edges and known not to fire for
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// others then there is nothing we can do - give up.
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if (Value != State) {
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State = LazyValueInfo::Unknown;
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break;
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}
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}
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if (State == LazyValueInfo::False) {
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// This case never fires - remove it.
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CI->getCaseSuccessor()->removePredecessor(BB);
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CI = SI->removeCase(CI);
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CE = SI->case_end();
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// The condition can be modified by removePredecessor's PHI simplification
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// logic.
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Cond = SI->getCondition();
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++NumDeadCases;
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Changed = true;
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continue;
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}
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if (State == LazyValueInfo::True) {
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// This case always fires. Arrange for the switch to be turned into an
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// unconditional branch by replacing the switch condition with the case
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// value.
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SI->setCondition(Case);
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NumDeadCases += SI->getNumCases();
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Changed = true;
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break;
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}
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// Increment the case iterator sense we didn't delete it.
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++CI;
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}
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if (Changed)
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// If the switch has been simplified to the point where it can be replaced
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// by a branch then do so now.
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ConstantFoldTerminator(BB);
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return Changed;
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}
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/// Infer nonnull attributes for the arguments at the specified callsite.
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static bool processCallSite(CallSite CS, LazyValueInfo *LVI) {
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SmallVector<unsigned, 4> ArgNos;
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unsigned ArgNo = 0;
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for (Value *V : CS.args()) {
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PointerType *Type = dyn_cast<PointerType>(V->getType());
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// Try to mark pointer typed parameters as non-null. We skip the
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// relatively expensive analysis for constants which are obviously either
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// null or non-null to start with.
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if (Type && !CS.paramHasAttr(ArgNo, Attribute::NonNull) &&
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!isa<Constant>(V) &&
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LVI->getPredicateAt(ICmpInst::ICMP_EQ, V,
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ConstantPointerNull::get(Type),
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CS.getInstruction()) == LazyValueInfo::False)
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ArgNos.push_back(ArgNo);
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ArgNo++;
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}
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assert(ArgNo == CS.arg_size() && "sanity check");
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if (ArgNos.empty())
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return false;
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AttributeList AS = CS.getAttributes();
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LLVMContext &Ctx = CS.getInstruction()->getContext();
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AS = AS.addParamAttribute(Ctx, ArgNos,
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Attribute::get(Ctx, Attribute::NonNull));
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CS.setAttributes(AS);
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return true;
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}
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// Helper function to rewrite srem and sdiv. As a policy choice, we choose not
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// to waste compile time on anything where the operands are local defs. While
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// LVI can sometimes reason about such cases, it's not its primary purpose.
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static bool hasLocalDefs(BinaryOperator *SDI) {
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for (Value *O : SDI->operands()) {
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auto *I = dyn_cast<Instruction>(O);
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if (I && I->getParent() == SDI->getParent())
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return true;
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}
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return false;
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}
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static bool hasPositiveOperands(BinaryOperator *SDI, LazyValueInfo *LVI) {
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Constant *Zero = ConstantInt::get(SDI->getType(), 0);
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for (Value *O : SDI->operands()) {
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auto Result = LVI->getPredicateAt(ICmpInst::ICMP_SGE, O, Zero, SDI);
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if (Result != LazyValueInfo::True)
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return false;
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}
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return true;
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}
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static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI) {
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if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI) ||
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!hasPositiveOperands(SDI, LVI))
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return false;
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++NumSRems;
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auto *BO = BinaryOperator::CreateURem(SDI->getOperand(0), SDI->getOperand(1),
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SDI->getName(), SDI);
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SDI->replaceAllUsesWith(BO);
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SDI->eraseFromParent();
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return true;
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}
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/// See if LazyValueInfo's ability to exploit edge conditions or range
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/// information is sufficient to prove the both operands of this SDiv are
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/// positive. If this is the case, replace the SDiv with a UDiv. Even for local
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/// conditions, this can sometimes prove conditions instcombine can't by
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/// exploiting range information.
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static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI) {
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if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI) ||
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!hasPositiveOperands(SDI, LVI))
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return false;
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++NumSDivs;
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auto *BO = BinaryOperator::CreateUDiv(SDI->getOperand(0), SDI->getOperand(1),
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SDI->getName(), SDI);
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BO->setIsExact(SDI->isExact());
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SDI->replaceAllUsesWith(BO);
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SDI->eraseFromParent();
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return true;
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}
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static bool processAShr(BinaryOperator *SDI, LazyValueInfo *LVI) {
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if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI))
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return false;
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Constant *Zero = ConstantInt::get(SDI->getType(), 0);
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if (LVI->getPredicateAt(ICmpInst::ICMP_SGE, SDI->getOperand(0), Zero, SDI) !=
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LazyValueInfo::True)
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return false;
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++NumAShrs;
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auto *BO = BinaryOperator::CreateLShr(SDI->getOperand(0), SDI->getOperand(1),
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SDI->getName(), SDI);
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BO->setIsExact(SDI->isExact());
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SDI->replaceAllUsesWith(BO);
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SDI->eraseFromParent();
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return true;
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}
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static bool processAdd(BinaryOperator *AddOp, LazyValueInfo *LVI) {
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typedef OverflowingBinaryOperator OBO;
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if (DontProcessAdds)
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return false;
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if (AddOp->getType()->isVectorTy() || hasLocalDefs(AddOp))
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return false;
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bool NSW = AddOp->hasNoSignedWrap();
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bool NUW = AddOp->hasNoUnsignedWrap();
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if (NSW && NUW)
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return false;
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BasicBlock *BB = AddOp->getParent();
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Value *LHS = AddOp->getOperand(0);
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Value *RHS = AddOp->getOperand(1);
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ConstantRange LRange = LVI->getConstantRange(LHS, BB, AddOp);
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// Initialize RRange only if we need it. If we know that guaranteed no wrap
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// range for the given LHS range is empty don't spend time calculating the
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// range for the RHS.
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Optional<ConstantRange> RRange;
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auto LazyRRange = [&] () {
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if (!RRange)
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RRange = LVI->getConstantRange(RHS, BB, AddOp);
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return RRange.getValue();
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};
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bool Changed = false;
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if (!NUW) {
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ConstantRange NUWRange = ConstantRange::makeGuaranteedNoWrapRegion(
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BinaryOperator::Add, LRange, OBO::NoUnsignedWrap);
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if (!NUWRange.isEmptySet()) {
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bool NewNUW = NUWRange.contains(LazyRRange());
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AddOp->setHasNoUnsignedWrap(NewNUW);
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Changed |= NewNUW;
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}
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}
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if (!NSW) {
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ConstantRange NSWRange = ConstantRange::makeGuaranteedNoWrapRegion(
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BinaryOperator::Add, LRange, OBO::NoSignedWrap);
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if (!NSWRange.isEmptySet()) {
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bool NewNSW = NSWRange.contains(LazyRRange());
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AddOp->setHasNoSignedWrap(NewNSW);
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Changed |= NewNSW;
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}
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}
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return Changed;
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}
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static Constant *getConstantAt(Value *V, Instruction *At, LazyValueInfo *LVI) {
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if (Constant *C = LVI->getConstant(V, At->getParent(), At))
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return C;
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// TODO: The following really should be sunk inside LVI's core algorithm, or
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// at least the outer shims around such.
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auto *C = dyn_cast<CmpInst>(V);
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if (!C) return nullptr;
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Value *Op0 = C->getOperand(0);
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Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
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if (!Op1) return nullptr;
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LazyValueInfo::Tristate Result =
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LVI->getPredicateAt(C->getPredicate(), Op0, Op1, At);
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if (Result == LazyValueInfo::Unknown)
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return nullptr;
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return (Result == LazyValueInfo::True) ?
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ConstantInt::getTrue(C->getContext()) :
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ConstantInt::getFalse(C->getContext());
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}
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static bool runImpl(Function &F, LazyValueInfo *LVI, const SimplifyQuery &SQ) {
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bool FnChanged = false;
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|
// Visiting in a pre-order depth-first traversal causes us to simplify early
|
|
// blocks before querying later blocks (which require us to analyze early
|
|
// blocks). Eagerly simplifying shallow blocks means there is strictly less
|
|
// work to do for deep blocks. This also means we don't visit unreachable
|
|
// blocks.
|
|
for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
|
|
bool BBChanged = false;
|
|
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
|
|
Instruction *II = &*BI++;
|
|
switch (II->getOpcode()) {
|
|
case Instruction::Select:
|
|
BBChanged |= processSelect(cast<SelectInst>(II), LVI);
|
|
break;
|
|
case Instruction::PHI:
|
|
BBChanged |= processPHI(cast<PHINode>(II), LVI, SQ);
|
|
break;
|
|
case Instruction::ICmp:
|
|
case Instruction::FCmp:
|
|
BBChanged |= processCmp(cast<CmpInst>(II), LVI);
|
|
break;
|
|
case Instruction::Load:
|
|
case Instruction::Store:
|
|
BBChanged |= processMemAccess(II, LVI);
|
|
break;
|
|
case Instruction::Call:
|
|
case Instruction::Invoke:
|
|
BBChanged |= processCallSite(CallSite(II), LVI);
|
|
break;
|
|
case Instruction::SRem:
|
|
BBChanged |= processSRem(cast<BinaryOperator>(II), LVI);
|
|
break;
|
|
case Instruction::SDiv:
|
|
BBChanged |= processSDiv(cast<BinaryOperator>(II), LVI);
|
|
break;
|
|
case Instruction::AShr:
|
|
BBChanged |= processAShr(cast<BinaryOperator>(II), LVI);
|
|
break;
|
|
case Instruction::Add:
|
|
BBChanged |= processAdd(cast<BinaryOperator>(II), LVI);
|
|
break;
|
|
}
|
|
}
|
|
|
|
Instruction *Term = BB->getTerminator();
|
|
switch (Term->getOpcode()) {
|
|
case Instruction::Switch:
|
|
BBChanged |= processSwitch(cast<SwitchInst>(Term), LVI);
|
|
break;
|
|
case Instruction::Ret: {
|
|
auto *RI = cast<ReturnInst>(Term);
|
|
// Try to determine the return value if we can. This is mainly here to
|
|
// simplify the writing of unit tests, but also helps to enable IPO by
|
|
// constant folding the return values of callees.
|
|
auto *RetVal = RI->getReturnValue();
|
|
if (!RetVal) break; // handle "ret void"
|
|
if (isa<Constant>(RetVal)) break; // nothing to do
|
|
if (auto *C = getConstantAt(RetVal, RI, LVI)) {
|
|
++NumReturns;
|
|
RI->replaceUsesOfWith(RetVal, C);
|
|
BBChanged = true;
|
|
}
|
|
}
|
|
};
|
|
|
|
FnChanged |= BBChanged;
|
|
}
|
|
|
|
return FnChanged;
|
|
}
|
|
|
|
bool CorrelatedValuePropagation::runOnFunction(Function &F) {
|
|
if (skipFunction(F))
|
|
return false;
|
|
|
|
LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
|
|
return runImpl(F, LVI, getBestSimplifyQuery(*this, F));
|
|
}
|
|
|
|
PreservedAnalyses
|
|
CorrelatedValuePropagationPass::run(Function &F, FunctionAnalysisManager &AM) {
|
|
|
|
LazyValueInfo *LVI = &AM.getResult<LazyValueAnalysis>(F);
|
|
bool Changed = runImpl(F, LVI, getBestSimplifyQuery(AM, F));
|
|
|
|
if (!Changed)
|
|
return PreservedAnalyses::all();
|
|
PreservedAnalyses PA;
|
|
PA.preserve<GlobalsAA>();
|
|
return PA;
|
|
}
|