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Chandler Carruth
c68d25fb58
the latter to the Transforms library. While the loop PM uses an analysis to form the IR units, the current plan is to have the PM itself establish and enforce both loop simplified form and LCSSA. This would be a layering violation in the analysis library. Fundamentally, the idea behind the loop PM is to *transform* loops in addition to running passes over them, so it really seemed like the most natural place to sink this was into the transforms library. We can't just move *everything* because we also have loop analyses that rely on a subset of the invariants. So this patch splits the the loop infrastructure into the analysis management that has to be part of the analysis library, and the transform-aware pass manager. This also required splitting the loop analyses' printer passes out to the transforms library, which makes sense to me as running these will transform the code into LCSSA in theory. I haven't split the unittest though because testing one component without the other seems nearly intractable. Differential Revision: https://reviews.llvm.org/D28452 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291662 91177308-0d34-0410-b5e6-96231b3b80d8
109 lines
3.8 KiB
C++
109 lines
3.8 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/LoopSimplifyCFG.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/AssumptionCache.h"
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#include "llvm/Analysis/BasicAliasAnalysis.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/Scalar.h"
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#include "llvm/Transforms/Scalar/LoopPassManager.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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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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PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, LoopAnalysisManager &AM,
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LoopStandardAnalysisResults &AR,
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LPMUpdater &) {
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if (!simplifyLoopCFG(L, AR.DT, AR.LI))
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return PreservedAnalyses::all();
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return getLoopPassPreservedAnalyses();
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}
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namespace {
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class LoopSimplifyCFGLegacyPass : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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LoopSimplifyCFGLegacyPass() : LoopPass(ID) {
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initializeLoopSimplifyCFGLegacyPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop *L, LPPassManager &) override {
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if (skipLoop(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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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addPreserved<DependenceAnalysisWrapperPass>();
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getLoopAnalysisUsage(AU);
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}
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};
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}
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char LoopSimplifyCFGLegacyPass::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
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"Simplify loop CFG", false, false)
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INITIALIZE_PASS_DEPENDENCY(LoopPass)
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INITIALIZE_PASS_END(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
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"Simplify loop CFG", false, false)
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Pass *llvm::createLoopSimplifyCFGPass() {
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return new LoopSimplifyCFGLegacyPass();
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}
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