llvm-project/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp

217 lines
7.7 KiB
C++

//===- LoopInstSimplify.cpp - Loop Instruction Simplification Pass --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs lightweight instruction simplification on loop bodies.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LoopInstSimplify.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/LoopPassManager.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
using namespace llvm;
#define DEBUG_TYPE "loop-instsimplify"
STATISTIC(NumSimplified, "Number of redundant instructions simplified");
static bool SimplifyLoopInst(Loop *L, DominatorTree *DT, LoopInfo *LI,
AssumptionCache *AC,
const TargetLibraryInfo *TLI) {
SmallVector<BasicBlock *, 8> ExitBlocks;
L->getUniqueExitBlocks(ExitBlocks);
array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
// The bit we are stealing from the pointer represents whether this basic
// block is the header of a subloop, in which case we only process its phis.
typedef PointerIntPair<BasicBlock *, 1> WorklistItem;
SmallVector<WorklistItem, 16> VisitStack;
SmallPtrSet<BasicBlock *, 32> Visited;
bool Changed = false;
bool LocalChanged;
do {
LocalChanged = false;
VisitStack.clear();
Visited.clear();
VisitStack.push_back(WorklistItem(L->getHeader(), false));
while (!VisitStack.empty()) {
WorklistItem Item = VisitStack.pop_back_val();
BasicBlock *BB = Item.getPointer();
bool IsSubloopHeader = Item.getInt();
const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
// Simplify instructions in the current basic block.
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
Instruction *I = &*BI++;
// The first time through the loop ToSimplify is empty and we try to
// simplify all instructions. On later iterations ToSimplify is not
// empty and we only bother simplifying instructions that are in it.
if (!ToSimplify->empty() && !ToSimplify->count(I))
continue;
// Don't bother simplifying unused instructions.
if (!I->use_empty()) {
Value *V = SimplifyInstruction(I, DL, TLI, DT, AC);
if (V && LI->replacementPreservesLCSSAForm(I, V)) {
// Mark all uses for resimplification next time round the loop.
for (User *U : I->users())
Next->insert(cast<Instruction>(U));
I->replaceAllUsesWith(V);
LocalChanged = true;
++NumSimplified;
}
}
if (RecursivelyDeleteTriviallyDeadInstructions(I, TLI)) {
// RecursivelyDeleteTriviallyDeadInstruction can remove more than one
// instruction, so simply incrementing the iterator does not work.
// When instructions get deleted re-iterate instead.
BI = BB->begin();
BE = BB->end();
LocalChanged = true;
}
if (IsSubloopHeader && !isa<PHINode>(I))
break;
}
// Add all successors to the worklist, except for loop exit blocks and the
// bodies of subloops. We visit the headers of loops so that we can
// process
// their phis, but we contract the rest of the subloop body and only
// follow
// edges leading back to the original loop.
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
++SI) {
BasicBlock *SuccBB = *SI;
if (!Visited.insert(SuccBB).second)
continue;
const Loop *SuccLoop = LI->getLoopFor(SuccBB);
if (SuccLoop && SuccLoop->getHeader() == SuccBB &&
L->contains(SuccLoop)) {
VisitStack.push_back(WorklistItem(SuccBB, true));
SmallVector<BasicBlock *, 8> SubLoopExitBlocks;
SuccLoop->getExitBlocks(SubLoopExitBlocks);
for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) {
BasicBlock *ExitBB = SubLoopExitBlocks[i];
if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB).second)
VisitStack.push_back(WorklistItem(ExitBB, false));
}
continue;
}
bool IsExitBlock =
std::binary_search(ExitBlocks.begin(), ExitBlocks.end(), SuccBB);
if (IsExitBlock)
continue;
VisitStack.push_back(WorklistItem(SuccBB, false));
}
}
// Place the list of instructions to simplify on the next loop iteration
// into ToSimplify.
std::swap(ToSimplify, Next);
Next->clear();
Changed |= LocalChanged;
} while (LocalChanged);
return Changed;
}
namespace {
class LoopInstSimplifyLegacyPass : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
LoopInstSimplifyLegacyPass() : LoopPass(ID) {
initializeLoopInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnLoop(Loop *L, LPPassManager &LPM) override {
if (skipLoop(L))
return false;
DominatorTreeWrapperPass *DTWP =
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
AssumptionCache *AC =
&getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
*L->getHeader()->getParent());
const TargetLibraryInfo *TLI =
&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
return SimplifyLoopInst(L, DT, LI, AC, TLI);
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.setPreservesCFG();
getLoopAnalysisUsage(AU);
}
};
}
PreservedAnalyses LoopInstSimplifyPass::run(Loop &L,
AnalysisManager<Loop> &AM) {
const auto &FAM =
AM.getResult<FunctionAnalysisManagerLoopProxy>(L).getManager();
Function *F = L.getHeader()->getParent();
// Use getCachedResult because Loop pass cannot trigger a function analysis.
auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(*F);
auto *LI = FAM.getCachedResult<LoopAnalysis>(*F);
auto *AC = FAM.getCachedResult<AssumptionAnalysis>(*F);
const auto *TLI = FAM.getCachedResult<TargetLibraryAnalysis>(*F);
assert((LI && AC && TLI) && "Analyses for Loop Inst Simplify not available");
if (!SimplifyLoopInst(&L, DT, LI, AC, TLI))
return PreservedAnalyses::all();
return getLoopPassPreservedAnalyses();
}
char LoopInstSimplifyLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(LoopInstSimplifyLegacyPass, "loop-instsimplify",
"Simplify instructions in loops", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LoopPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(LoopInstSimplifyLegacyPass, "loop-instsimplify",
"Simplify instructions in loops", false, false)
Pass *llvm::createLoopInstSimplifyPass() {
return new LoopInstSimplifyLegacyPass();
}