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Add support for eliminate stores to stack-allocated memory locations at the end

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of a function.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39754 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2007-07-11 21:06:56 +00:00
parent 2655adb3b2
commit 6f46d65104
1 changed files with 45 additions and 1 deletions
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46
lib/Transforms/Scalar/FastDSE.cpp
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@ -73,7 +73,7 @@ bool FDSE::runOnBasicBlock(BasicBlock &BB) {
// Do a top-down walk on the BB
for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ++BBI) {
// If we find a store...
// If we find a store or a free...
if (isa<StoreInst>(BBI) || isa<FreeInst>(BBI)) {
Value* pointer = 0;
if (StoreInst* S = dyn_cast<StoreInst>(BBI))
@ -111,6 +111,50 @@ bool FDSE::runOnBasicBlock(BasicBlock &BB) {
}
}
// If this block ends in a return, unwind, unreachable, and eventually
// tailcall, then all allocas are dead at its end.
if (BB.getTerminator()->getNumSuccessors() == 0) {
// Pointers alloca'd in this function are dead in the end block
SmallPtrSet<AllocaInst*, 4> deadPointers;
// Find all of the alloca'd pointers in the entry block
BasicBlock *Entry = BB.getParent()->begin();
for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
deadPointers.insert(AI);
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
if (deadPointers.empty())
break;
// If we find a store whose pointer is dead...
if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
if (deadPointers.count(S->getPointerOperand())){
// Remove it!
MD.removeInstruction(S);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
possiblyDead.insert(D);
BBI++;
S->eraseFromParent();
NumFastStores++;
MadeChange = true;
}
// If we encounter a use of the pointer, it is no longer considered dead
} else if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
deadPointers.erase(L->getPointerOperand());
} else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
deadPointers.erase(V->getOperand(0));
}
}
}
// Do a trivial DCE
while (!possiblyDead.empty()) {
Instruction *I = possiblyDead.back();