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abomination. For starters, this API is incredibly slow. In order to lookup the name of a pass it must take a memory fence to acquire a pointer to the managed static pass registry, and then potentially acquire locks while it consults this registry for information about what passes exist by that name. This stops the world of LLVMs in your process no matter how little they cared about the result. To make this more joyful, you'll note that we are preserving many passes which *do not exist* any more, or are not even analyses which one might wish to have be preserved. This means we do all the work only to say "nope" with no error to the user. String-based APIs are a *bad idea*. String-based APIs that cannot produce any meaningful error are an even worse idea. =/ I have a patch that simply removes this API completely, but I'm hesitant to commit it as I don't really want to perniciously break out-of-tree users of the old pass manager. I'd rather they just have to migrate to the new one at some point. If others disagree and would like me to kill it with fire, just say the word. =] git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227294 91177308-0d34-0410-b5e6-96231b3b80d8
197 lines
6.9 KiB
C++
197 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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DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
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const DataLayout *DL = DLP ? &DLP->getDataLayout() : nullptr;
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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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// 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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