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//===- ConstantProp.cpp - Code to perform Simple Constant Propogation -----===//
//
// This file implements constant propogation and merging:
//
// Specifically, this:
// * Converts instructions like "add int 1, 2" into 3
//
// Notice that:
// * This pass has a habit of making definitions be dead. It is a good idea
// to to run a DIE pass sometime after running this pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ConstantHandling.h"
#include "llvm/Instruction.h"
#include "llvm/Pass.h"
#include "llvm/Support/InstIterator.h"
#include "Support/StatisticReporter.h"
#include <set>
static Statistic<> NumInstKilled("constprop - Number of instructions killed");
namespace {
struct ConstantPropogation : public FunctionPass {
const char *getPassName() const { return "Simple Constant Propogation"; }
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.preservesCFG();
}
};
}
Pass *createConstantPropogationPass() {
return new ConstantPropogation();
}
bool ConstantPropogation::runOnFunction(Function &F) {
// Initialize the worklist to all of the instructions ready to process...
std::set<Instruction*> WorkList(inst_begin(F), inst_end(F));
bool Changed = false;
while (!WorkList.empty()) {
Instruction *I = *WorkList.begin();
WorkList.erase(WorkList.begin()); // Get an element from the worklist...
if (!I->use_empty()) // Don't muck with dead instructions...
if (Constant *C = ConstantFoldInstruction(I)) {
// Add all of the users of this instruction to the worklist, they might
// be constant propogatable now...
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI)
WorkList.insert(cast<Instruction>(*UI));
// Replace all of the uses of a variable with uses of the constant.
I->replaceAllUsesWith(C);
// We made a change to the function...
Changed = true;
++NumInstKilled;
}
}
return Changed;
}
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