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Add support for replacement of formal arguments with simpler expressions.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13689 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-05-23 21:19:55 +00:00
parent 08005dfdc9
commit 057f78ab4e
1 changed files with 23 additions and 2 deletions

25
lib/Transforms/Scalar/GCSE.cpp

@ -1,4 +1,4 @@
//===-- GCSE.cpp - SSA based Global Common Subexpr Elimination ------------===//
//===-- GCSE.cpp - SSA-based Global Common Subexpression Elimination ------===//
//
// The LLVM Compiler Infrastructure
//
@ -33,6 +33,8 @@ namespace {
Statistic<> NumCallRemoved("gcse", "Number of calls removed");
Statistic<> NumNonInsts ("gcse", "Number of instructions removed due "
"to non-instruction values");
Statistic<> NumArgsRepl ("gcse", "Number of function arguments replaced "
"with constant values");
struct GCSE : public FunctionPass {
virtual bool runOnFunction(Function &F);
@ -68,6 +70,25 @@ bool GCSE::runOnFunction(Function &F) {
std::vector<Value*> EqualValues;
// Check for value numbers of arguments. If the value numbering
// implementation can prove that an incoming argument is a constant or global
// value address, substitute it, making the argument dead.
for (Function::aiterator AI = F.abegin(), E = F.aend(); AI != E; ++AI)
if (!AI->use_empty()) {
VN.getEqualNumberNodes(AI, EqualValues);
if (!EqualValues.empty()) {
for (unsigned i = 0, e = EqualValues.size(); i != e; ++i)
if (isa<Constant>(EqualValues[i]) ||
isa<GlobalValue>(EqualValues[i])) {
AI->replaceAllUsesWith(EqualValues[i]);
++NumArgsRepl;
Changed = true;
break;
}
EqualValues.clear();
}
}
// Traverse the CFG of the function in dominator order, so that we see each
// instruction after we see its operands.
for (df_iterator<DominatorTree::Node*> DI = df_begin(DT.getRootNode()),
@ -161,7 +182,7 @@ void GCSE::ReplaceInstructionWith(Instruction *I, Value *V) {
++NumInstRemoved; // Keep track of number of insts eliminated
// Update value numbering
getAnalysis<ValueNumbering>().deleteInstruction(I);
getAnalysis<ValueNumbering>().deleteValue(I);
// If we are not replacing the instruction with a constant, we cannot do
// anything special.