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Apparently, the style needs to be agreed upon first. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240390 91177308-0d34-0410-b5e6-96231b3b80d8
196 lines
6.9 KiB
C++
196 lines
6.9 KiB
C++
//===- LoopInstSimplify.cpp - Loop Instruction 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 pass performs lightweight instruction simplification on loop bodies.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/STLExtras.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/InstructionSimplify.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/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/Support/Debug.h"
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#include "llvm/Analysis/TargetLibraryInfo.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 "loop-instsimplify"
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STATISTIC(NumSimplified, "Number of redundant instructions simplified");
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namespace {
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class LoopInstSimplify : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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LoopInstSimplify() : LoopPass(ID) {
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initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop*, LPPassManager&) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<AssumptionCacheTracker>();
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AU.addRequired<LoopInfoWrapperPass>();
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.addPreservedID(LCSSAID);
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AU.addPreserved<ScalarEvolution>();
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AU.addRequired<TargetLibraryInfoWrapperPass>();
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}
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};
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}
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char LoopInstSimplify::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
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"Simplify instructions in loops", false, false)
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INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
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"Simplify instructions in loops", false, false)
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Pass *llvm::createLoopInstSimplifyPass() {
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return new LoopInstSimplify();
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}
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bool LoopInstSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
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if (skipOptnoneFunction(L))
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return false;
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DominatorTreeWrapperPass *DTWP =
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getAnalysisIfAvailable<DominatorTreeWrapperPass>();
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DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
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LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
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const TargetLibraryInfo *TLI =
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&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
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auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
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*L->getHeader()->getParent());
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SmallVector<BasicBlock*, 8> ExitBlocks;
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L->getUniqueExitBlocks(ExitBlocks);
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array_pod_sort(ExitBlocks.begin(), ExitBlocks.end());
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SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
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// The bit we are stealing from the pointer represents whether this basic
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// block is the header of a subloop, in which case we only process its phis.
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typedef PointerIntPair<BasicBlock*, 1> WorklistItem;
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SmallVector<WorklistItem, 16> VisitStack;
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SmallPtrSet<BasicBlock*, 32> Visited;
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bool Changed = false;
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bool LocalChanged;
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do {
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LocalChanged = false;
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VisitStack.clear();
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Visited.clear();
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VisitStack.push_back(WorklistItem(L->getHeader(), false));
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while (!VisitStack.empty()) {
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WorklistItem Item = VisitStack.pop_back_val();
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BasicBlock *BB = Item.getPointer();
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bool IsSubloopHeader = Item.getInt();
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const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
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// Simplify instructions in the current basic block.
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for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
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Instruction *I = BI++;
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// The first time through the loop ToSimplify is empty and we try to
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// simplify all instructions. On later iterations ToSimplify is not
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// empty and we only bother simplifying instructions that are in it.
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if (!ToSimplify->empty() && !ToSimplify->count(I))
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continue;
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// Don't bother simplifying unused instructions.
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if (!I->use_empty()) {
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Value *V = SimplifyInstruction(I, DL, TLI, DT, &AC);
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if (V && LI->replacementPreservesLCSSAForm(I, V)) {
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// Mark all uses for resimplification next time round the loop.
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for (User *U : I->users())
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Next->insert(cast<Instruction>(U));
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I->replaceAllUsesWith(V);
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LocalChanged = true;
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++NumSimplified;
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}
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}
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bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
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if (res) {
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// RecursivelyDeleteTriviallyDeadInstruction can remove
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// more than one instruction, so simply incrementing the
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// iterator does not work. When instructions get deleted
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// re-iterate instead.
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BI = BB->begin(); BE = BB->end();
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LocalChanged |= res;
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}
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if (IsSubloopHeader && !isa<PHINode>(I))
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break;
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}
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// Add all successors to the worklist, except for loop exit blocks and the
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// bodies of subloops. We visit the headers of loops so that we can process
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// their phis, but we contract the rest of the subloop body and only follow
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// edges leading back to the original loop.
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
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++SI) {
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BasicBlock *SuccBB = *SI;
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if (!Visited.insert(SuccBB).second)
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continue;
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const Loop *SuccLoop = LI->getLoopFor(SuccBB);
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if (SuccLoop && SuccLoop->getHeader() == SuccBB
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&& L->contains(SuccLoop)) {
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VisitStack.push_back(WorklistItem(SuccBB, true));
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SmallVector<BasicBlock*, 8> SubLoopExitBlocks;
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SuccLoop->getExitBlocks(SubLoopExitBlocks);
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for (unsigned i = 0; i < SubLoopExitBlocks.size(); ++i) {
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BasicBlock *ExitBB = SubLoopExitBlocks[i];
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if (LI->getLoopFor(ExitBB) == L && Visited.insert(ExitBB).second)
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VisitStack.push_back(WorklistItem(ExitBB, false));
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}
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continue;
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}
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bool IsExitBlock = std::binary_search(ExitBlocks.begin(),
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ExitBlocks.end(), SuccBB);
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if (IsExitBlock)
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continue;
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VisitStack.push_back(WorklistItem(SuccBB, false));
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}
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}
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// Place the list of instructions to simplify on the next loop iteration
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// into ToSimplify.
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std::swap(ToSimplify, Next);
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Next->clear();
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Changed |= LocalChanged;
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} while (LocalChanged);
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return Changed;
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}
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