2003-05-20 21:01:22 +00:00
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//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
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2005-04-21 23:48:37 +00:00
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//
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2003-10-20 19:43:21 +00:00
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// The LLVM Compiler Infrastructure
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//
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2007-12-29 20:36:04 +00:00
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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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2005-04-21 23:48:37 +00:00
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//
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2003-10-20 19:43:21 +00:00
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//===----------------------------------------------------------------------===//
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2001-06-06 20:29:01 +00:00
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//
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2003-05-20 21:01:22 +00:00
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// This file implements constant propagation and merging:
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2001-06-06 20:29:01 +00:00
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//
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// Specifically, this:
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2002-05-06 18:21:31 +00:00
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// * Converts instructions like "add int 1, 2" into 3
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2001-06-06 20:29:01 +00:00
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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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2008-08-01 12:23:49 +00:00
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// to run a DIE pass sometime after running this pass.
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2001-06-06 20:29:01 +00:00
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//
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//===----------------------------------------------------------------------===//
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2006-12-19 21:40:18 +00:00
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#define DEBUG_TYPE "constprop"
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2002-05-07 20:03:00 +00:00
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#include "llvm/Transforms/Scalar.h"
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2007-01-30 23:46:24 +00:00
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#include "llvm/Analysis/ConstantFolding.h"
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2004-01-12 19:15:20 +00:00
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#include "llvm/Constant.h"
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2002-05-07 18:10:55 +00:00
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#include "llvm/Instruction.h"
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2002-02-26 21:46:54 +00:00
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#include "llvm/Pass.h"
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2002-05-06 18:21:31 +00:00
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#include "llvm/Support/InstIterator.h"
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2004-09-01 22:55:40 +00:00
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#include "llvm/ADT/Statistic.h"
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2002-05-06 18:21:31 +00:00
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#include <set>
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2004-01-09 06:02:20 +00:00
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using namespace llvm;
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2003-11-11 22:41:34 +00:00
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2006-12-19 21:40:18 +00:00
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STATISTIC(NumInstKilled, "Number of instructions killed");
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2002-10-01 22:38:41 +00:00
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2006-12-19 21:40:18 +00:00
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namespace {
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2009-09-02 06:11:42 +00:00
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struct ConstantPropagation : public FunctionPass {
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2007-05-06 13:37:16 +00:00
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static char ID; // Pass identification, replacement for typeid
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2008-09-04 17:05:41 +00:00
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ConstantPropagation() : FunctionPass(&ID) {}
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2007-05-01 21:15:47 +00:00
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2002-06-25 16:13:24 +00:00
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bool runOnFunction(Function &F);
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2002-04-28 21:27:06 +00:00
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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2002-10-21 20:00:28 +00:00
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AU.setPreservesCFG();
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2002-04-28 21:27:06 +00:00
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}
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2002-02-26 21:46:54 +00:00
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};
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}
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2001-06-06 20:29:01 +00:00
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2008-05-13 00:00:25 +00:00
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char ConstantPropagation::ID = 0;
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static RegisterPass<ConstantPropagation>
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X("constprop", "Simple constant propagation");
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2004-09-20 04:43:15 +00:00
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FunctionPass *llvm::createConstantPropagationPass() {
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2003-05-20 21:01:22 +00:00
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return new ConstantPropagation();
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2001-06-06 20:29:01 +00:00
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}
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2002-02-26 21:46:54 +00:00
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2002-05-06 18:21:31 +00:00
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2003-05-20 21:01:22 +00:00
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bool ConstantPropagation::runOnFunction(Function &F) {
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2002-05-06 18:21:31 +00:00
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// Initialize the worklist to all of the instructions ready to process...
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2004-04-27 15:13:33 +00:00
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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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2002-05-06 18:21:31 +00:00
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bool Changed = false;
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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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2009-11-06 04:27:31 +00:00
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if (Constant *C = ConstantFoldInstruction(I)) {
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2002-05-06 18:21:31 +00:00
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// Add all of the users of this instruction to the worklist, they might
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2003-05-20 21:01:22 +00:00
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// be constant propagatable now...
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2002-05-06 18:21:31 +00:00
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for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
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UI != UE; ++UI)
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WorkList.insert(cast<Instruction>(*UI));
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2005-04-21 23:48:37 +00:00
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2002-05-06 18:21:31 +00:00
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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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2002-05-10 15:38:35 +00:00
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2004-04-13 19:28:20 +00:00
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// Remove the dead instruction.
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WorkList.erase(I);
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2008-06-21 22:08:46 +00:00
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I->eraseFromParent();
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2004-04-13 19:28:20 +00:00
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2002-05-06 18:21:31 +00:00
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// We made a change to the function...
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Changed = true;
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2002-05-10 15:38:35 +00:00
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++NumInstKilled;
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2002-05-06 18:21:31 +00:00
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}
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}
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return Changed;
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}
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