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88fd126216
The pass is really just a means of accessing a cached instance of the TargetLibraryInfo object, and this way we can re-use that object for the new pass manager as its result. Lots of delta, but nothing interesting happening here. This is the common pattern that is developing to allow analyses to live in both the old and new pass manager -- a wrapper pass in the old pass manager emulates the separation intrinsic to the new pass manager between the result and pass for analyses. llvm-svn: 226157
101 lines
3.3 KiB
C++
101 lines
3.3 KiB
C++
//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
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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 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/Transforms/Scalar.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/IR/Constant.h"
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#include "llvm/IR/DataLayout.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/Analysis/TargetLibraryInfo.h"
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#include <set>
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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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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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// Initialize the worklist to all of the instructions ready to process...
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std::set<Instruction*> WorkList;
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for(inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
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WorkList.insert(&*i);
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}
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bool Changed = false;
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DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
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const DataLayout *DL = DLP ? &DLP->getDataLayout() : nullptr;
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TargetLibraryInfo *TLI =
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&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
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while (!WorkList.empty()) {
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Instruction *I = *WorkList.begin();
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WorkList.erase(WorkList.begin()); // Get an 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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// 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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WorkList.insert(cast<Instruction>(U));
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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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// Remove the dead instruction.
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WorkList.erase(I);
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I->eraseFromParent();
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// We made a change to the function...
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Changed = true;
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++NumInstKilled;
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}
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}
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return Changed;
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}
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