9c27b59cec
Summary: This is the first change to enable the TLI to be built per-function so that -fno-builtin* handling can be migrated to use function attributes. See discussion on D61634 for background. This is an enabler for fixing handling of these options for LTO, for example. This change should not affect behavior, as the provided function is not yet used to build a specifically per-function TLI, but rather enables that migration. Most of the changes were very mechanical, e.g. passing a Function to the legacy analysis pass's getTLI interface, or in Module level cases, adding a callback. This is similar to the way the per-function TTI analysis works. There was one place where we were looking for builtins but not in the context of a specific function. See FindCXAAtExit in lib/Transforms/IPO/GlobalOpt.cpp. I'm somewhat concerned my workaround could provide the wrong behavior in some corner cases. Suggestions welcome. Reviewers: chandlerc, hfinkel Subscribers: arsenm, dschuff, jvesely, nhaehnle, mehdi_amini, javed.absar, sbc100, jgravelle-google, eraman, aheejin, steven_wu, george.burgess.iv, dexonsmith, jfb, asbirlea, gchatelet, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D66428 llvm-svn: 371284
121 lines
4.1 KiB
C++
121 lines
4.1 KiB
C++
//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements constant propagation and merging:
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//
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// Specifically, this:
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// * Converts instructions like "add int 1, 2" into 3
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//
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// Notice that:
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// * This pass has a habit of making definitions be dead. It is a good idea
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// to run a DIE pass sometime after running this pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/SmallPtrSet.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/ConstantFolding.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/DebugCounter.h"
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#include "llvm/Transforms/Scalar.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 "constprop"
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STATISTIC(NumInstKilled, "Number of instructions killed");
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DEBUG_COUNTER(CPCounter, "constprop-transform",
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"Controls which instructions are killed");
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namespace {
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struct ConstantPropagation : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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ConstantPropagation() : FunctionPass(ID) {
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initializeConstantPropagationPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<TargetLibraryInfoWrapperPass>();
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}
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};
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}
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char ConstantPropagation::ID = 0;
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INITIALIZE_PASS_BEGIN(ConstantPropagation, "constprop",
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"Simple constant propagation", false, false)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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INITIALIZE_PASS_END(ConstantPropagation, "constprop",
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"Simple constant propagation", false, false)
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FunctionPass *llvm::createConstantPropagationPass() {
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return new ConstantPropagation();
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}
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bool ConstantPropagation::runOnFunction(Function &F) {
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if (skipFunction(F))
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return false;
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// Initialize the worklist to all of the instructions ready to process...
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SmallPtrSet<Instruction *, 16> WorkList;
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// The SmallVector of WorkList ensures that we do iteration at stable order.
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// We use two containers rather than one SetVector, since remove is
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// linear-time, and we don't care enough to remove from Vec.
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SmallVector<Instruction *, 16> WorkListVec;
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for (Instruction &I : instructions(&F)) {
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WorkList.insert(&I);
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WorkListVec.push_back(&I);
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}
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bool Changed = false;
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const DataLayout &DL = F.getParent()->getDataLayout();
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TargetLibraryInfo *TLI =
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&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
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while (!WorkList.empty()) {
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SmallVector<Instruction*, 16> NewWorkListVec;
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for (auto *I : WorkListVec) {
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WorkList.erase(I); // Remove element from the worklist...
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if (!I->use_empty()) // Don't muck with dead instructions...
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if (Constant *C = ConstantFoldInstruction(I, DL, TLI)) {
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if (!DebugCounter::shouldExecute(CPCounter))
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continue;
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// Add all of the users of this instruction to the worklist, they might
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// be constant propagatable now...
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for (User *U : I->users()) {
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// If user not in the set, then add it to the vector.
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if (WorkList.insert(cast<Instruction>(U)).second)
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NewWorkListVec.push_back(cast<Instruction>(U));
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}
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// Replace all of the uses of a variable with uses of the constant.
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I->replaceAllUsesWith(C);
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if (isInstructionTriviallyDead(I, TLI)) {
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I->eraseFromParent();
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++NumInstKilled;
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}
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// We made a change to the function...
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Changed = true;
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}
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}
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WorkListVec = std::move(NewWorkListVec);
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}
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return Changed;
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}
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