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488b678a49
- Fix loop nest. - Use RetVals.size() - Check for null return value. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48605 91177308-0d34-0410-b5e6-96231b3b80d8
237 lines
8.4 KiB
C++
237 lines
8.4 KiB
C++
//===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
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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 implements an _extremely_ simple interprocedural constant
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// propagation pass. It could certainly be improved in many different ways,
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// like using a worklist. This pass makes arguments dead, but does not remove
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// them. The existing dead argument elimination pass should be run after this
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// to clean up the mess.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "ipconstprop"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/SmallVector.h"
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using namespace llvm;
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STATISTIC(NumArgumentsProped, "Number of args turned into constants");
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STATISTIC(NumReturnValProped, "Number of return values turned into constants");
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namespace {
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/// IPCP - The interprocedural constant propagation pass
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///
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struct VISIBILITY_HIDDEN IPCP : public ModulePass {
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static char ID; // Pass identification, replacement for typeid
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IPCP() : ModulePass((intptr_t)&ID) {}
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bool runOnModule(Module &M);
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private:
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bool PropagateConstantsIntoArguments(Function &F);
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bool PropagateConstantReturn(Function &F);
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};
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char IPCP::ID = 0;
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RegisterPass<IPCP> X("ipconstprop", "Interprocedural constant propagation");
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}
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ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }
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bool IPCP::runOnModule(Module &M) {
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bool Changed = false;
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bool LocalChange = true;
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// FIXME: instead of using smart algorithms, we just iterate until we stop
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// making changes.
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while (LocalChange) {
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LocalChange = false;
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
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if (!I->isDeclaration()) {
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// Delete any klingons.
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I->removeDeadConstantUsers();
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if (I->hasInternalLinkage())
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LocalChange |= PropagateConstantsIntoArguments(*I);
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Changed |= PropagateConstantReturn(*I);
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}
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Changed |= LocalChange;
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}
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return Changed;
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}
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/// PropagateConstantsIntoArguments - Look at all uses of the specified
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/// function. If all uses are direct call sites, and all pass a particular
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/// constant in for an argument, propagate that constant in as the argument.
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///
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bool IPCP::PropagateConstantsIntoArguments(Function &F) {
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if (F.arg_empty() || F.use_empty()) return false; // No arguments? Early exit.
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std::vector<std::pair<Constant*, bool> > ArgumentConstants;
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ArgumentConstants.resize(F.arg_size());
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unsigned NumNonconstant = 0;
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for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I)
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if (!isa<Instruction>(*I))
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return false; // Used by a non-instruction, do not transform
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else {
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CallSite CS = CallSite::get(cast<Instruction>(*I));
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if (CS.getInstruction() == 0 ||
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CS.getCalledFunction() != &F)
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return false; // Not a direct call site?
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// Check out all of the potentially constant arguments
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CallSite::arg_iterator AI = CS.arg_begin();
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Function::arg_iterator Arg = F.arg_begin();
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for (unsigned i = 0, e = ArgumentConstants.size(); i != e;
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++i, ++AI, ++Arg) {
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if (*AI == &F) return false; // Passes the function into itself
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if (!ArgumentConstants[i].second) {
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if (Constant *C = dyn_cast<Constant>(*AI)) {
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if (!ArgumentConstants[i].first)
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ArgumentConstants[i].first = C;
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else if (ArgumentConstants[i].first != C) {
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// Became non-constant
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ArgumentConstants[i].second = true;
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++NumNonconstant;
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if (NumNonconstant == ArgumentConstants.size()) return false;
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}
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} else if (*AI != &*Arg) { // Ignore recursive calls with same arg
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// This is not a constant argument. Mark the argument as
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// non-constant.
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ArgumentConstants[i].second = true;
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++NumNonconstant;
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if (NumNonconstant == ArgumentConstants.size()) return false;
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}
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}
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}
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}
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// If we got to this point, there is a constant argument!
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assert(NumNonconstant != ArgumentConstants.size());
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Function::arg_iterator AI = F.arg_begin();
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bool MadeChange = false;
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for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI)
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// Do we have a constant argument!?
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if (!ArgumentConstants[i].second && !AI->use_empty()) {
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Value *V = ArgumentConstants[i].first;
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if (V == 0) V = UndefValue::get(AI->getType());
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AI->replaceAllUsesWith(V);
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++NumArgumentsProped;
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MadeChange = true;
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}
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return MadeChange;
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}
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// Check to see if this function returns a constant. If so, replace all callers
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// that user the return value with the returned valued. If we can replace ALL
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// callers,
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bool IPCP::PropagateConstantReturn(Function &F) {
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if (F.getReturnType() == Type::VoidTy)
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return false; // No return value.
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// Check to see if this function returns a constant.
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SmallVector<Value *,4> RetVals;
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const StructType *STy = dyn_cast<StructType>(F.getReturnType());
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if (STy)
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RetVals.assign(STy->getNumElements(), 0);
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else
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RetVals.push_back(0);
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for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
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if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
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unsigned RetValsSize = RetVals.size();
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assert (RetValsSize == RI->getNumOperands() && "Invalid ReturnInst operands!");
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for (unsigned i = 0; i < RetValsSize; ++i) {
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if (isa<UndefValue>(RI->getOperand(i))) {
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// Ignore
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} else if (Constant *C = dyn_cast<Constant>(RI->getOperand(i))) {
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Value *RV = RetVals[i];
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if (RV == 0)
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RetVals[i] = C;
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else if (RV != C)
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return false; // Does not return the same constant.
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} else {
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return false; // Does not return a constant.
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}
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}
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}
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if (STy) {
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for (unsigned i = 0, e = RetVals.size(); i < e; ++i)
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if (RetVals[i] == 0)
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RetVals[i] = UndefValue::get(STy->getElementType(i));
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} else {
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if (RetVals.size() == 1)
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if (RetVals[0] == 0)
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RetVals[0] = UndefValue::get(F.getReturnType());
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}
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// If we got here, the function returns a constant value. Loop over all
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// users, replacing any uses of the return value with the returned constant.
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bool ReplacedAllUsers = true;
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bool MadeChange = false;
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for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I)
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if (!isa<Instruction>(*I))
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ReplacedAllUsers = false;
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else {
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CallSite CS = CallSite::get(cast<Instruction>(*I));
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if (CS.getInstruction() == 0 ||
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CS.getCalledFunction() != &F) {
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ReplacedAllUsers = false;
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} else {
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Instruction *Call = CS.getInstruction();
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if (!Call->use_empty()) {
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if (RetVals.size() == 1)
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Call->replaceAllUsesWith(RetVals[0]);
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else {
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for(Value::use_iterator CUI = Call->use_begin(), CUE = Call->use_end();
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CUI != CUE; ++CUI) {
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GetResultInst *GR = cast<GetResultInst>(CUI);
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if (RetVals[GR->getIndex()]) {
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GR->replaceAllUsesWith(RetVals[GR->getIndex()]);
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GR->eraseFromParent();
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}
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}
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}
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MadeChange = true;
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}
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}
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}
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// If we replace all users with the returned constant, and there can be no
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// other callers of the function, replace the constant being returned in the
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// function with an undef value.
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if (ReplacedAllUsers && F.hasInternalLinkage()) {
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for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
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if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
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for (unsigned i = 0, e = RetVals.size(); i < e; ++i) {
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Value *RetVal = RetVals[i];
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if (isa<UndefValue>(RetVal))
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continue;
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Value *RV = UndefValue::get(RetVal->getType());
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if (RI->getOperand(i) != RV) {
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RI->setOperand(i, RV);
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MadeChange = true;
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}
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}
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}
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}
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}
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if (MadeChange) ++NumReturnValProped;
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return MadeChange;
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}
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