101 lines
3.4 KiB
C++
101 lines
3.4 KiB
C++
//===--------- LoopSimplifyCFG.cpp - Loop CFG Simplification Pass ---------===//
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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 Loop SimplifyCFG Pass. This pass is responsible for
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// basic loop CFG cleanup, primarily to assist other loop passes. If you
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// encounter a noncanonical CFG construct that causes another loop pass to
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// perform suboptimally, this is the place to fix it up.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.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/AliasAnalysis.h"
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#include "llvm/Analysis/BasicAliasAnalysis.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/DependenceAnalysis.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/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/Dominators.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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using namespace llvm;
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#define DEBUG_TYPE "loop-simplifycfg"
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namespace {
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class LoopSimplifyCFG : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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LoopSimplifyCFG() : LoopPass(ID) {
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initializeLoopSimplifyCFGPass(*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop *L, LPPassManager &) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addPreserved<DependenceAnalysis>();
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getLoopAnalysisUsage(AU);
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}
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};
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}
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char LoopSimplifyCFG::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
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false, false)
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INITIALIZE_PASS_DEPENDENCY(LoopPass)
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INITIALIZE_PASS_END(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
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false, false)
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Pass *llvm::createLoopSimplifyCFGPass() { return new LoopSimplifyCFG(); }
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static bool simplifyLoopCFG(Loop *L, DominatorTree *DT, LoopInfo *LI) {
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bool Changed = false;
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// Copy blocks into a temporary array to avoid iterator invalidation issues
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// as we remove them.
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SmallVector<WeakVH, 16> Blocks(L->blocks());
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for (auto &Block : Blocks) {
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// Attempt to merge blocks in the trivial case. Don't modify blocks which
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// belong to other loops.
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BasicBlock *Succ = cast_or_null<BasicBlock>(Block);
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if (!Succ)
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continue;
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BasicBlock *Pred = Succ->getSinglePredecessor();
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if (!Pred || !Pred->getSingleSuccessor() || LI->getLoopFor(Pred) != L)
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continue;
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// Pred is going to disappear, so we need to update the loop info.
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if (L->getHeader() == Pred)
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L->moveToHeader(Succ);
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LI->removeBlock(Pred);
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MergeBasicBlockIntoOnlyPred(Succ, DT);
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Changed = true;
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}
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return Changed;
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}
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/// runOnLoop - Perform basic CFG simplifications to assist other loop passes.
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/// For now, this only attempts to merge blocks in the trivial case.
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bool LoopSimplifyCFG::runOnLoop(Loop *L, LPPassManager &) {
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if (skipOptnoneFunction(L))
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return false;
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DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
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return simplifyLoopCFG(L, DT, LI);
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}
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