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two changes to DSE that shouldn't affect anything:

Browse Source 
1. Don't bother trying to optimize:

lifetime.end(ptr)
store(ptr)

as it is undefined, and therefore shouldn't exist.

2. Move the 'storing a loaded pointer' xform up, simplifying
  the may-aliased store code.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120359 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-11-30 00:01:19 +00:00
parent 8e0c7b5287
commit 0f53f592ad
1 changed files with 33 additions and 63 deletions
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96
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -204,10 +204,10 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
// If we find a store or a free, get its memory dependence.
if (!doesClobberMemory(Inst) && !isFreeCall(Inst))
continue;
MemDepResult InstDep = MD.getDependency(Inst);
// Ignore non-local stores.
// Ignore non-local store liveness.
// FIXME: cross-block DSE would be fun. :)
if (InstDep.isNonLocal()) continue;
@ -216,55 +216,7 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
MadeChange |= handleFreeWithNonTrivialDependency(F, Inst, InstDep);
continue;
}
if (!InstDep.isDef()) {
// If this is a may-aliased store that is clobbering the store value, we
// can keep searching past it for another must-aliased pointer that stores
// to the same location. For example, in:
// store -> P
// store -> Q
// store -> P
// we can remove the first store to P even though we don't know if P and Q
// alias.
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
AliasAnalysis::Location Loc =
getAnalysis<AliasAnalysis>().getLocation(SI);
while (InstDep.isClobber() && isa<StoreInst>(InstDep.getInst()) &&
InstDep.getInst() != &BB.front())
InstDep = MD.getPointerDependencyFrom(Loc, false, InstDep.getInst(),
&BB);
}
// If not a definite must-alias store dependency, ignore it. If this is a
// load from the same pointer, we don't want to transform load+store into
// a noop.
if (!InstDep.isDef() || !isa<StoreInst>(InstDep.getInst()))
continue;
}
// If this is a store-store dependence, then the previous store is dead so
// long as this store is at least as big as it.
if (doesClobberMemory(InstDep.getInst())) {
Instruction *DepStore = InstDep.getInst();
if (isStoreAtLeastAsWideAs(Inst, DepStore, TD) &&
isElidable(DepStore)) {
// Delete the store and now-dead instructions that feed it.
DeleteDeadInstruction(DepStore);
++NumFastStores;
MadeChange = true;
// DeleteDeadInstruction can delete the current instruction in loop
// cases, reset BBI.
BBI = Inst;
if (BBI != BB.begin())
--BBI;
continue;
}
}
if (!isElidable(Inst))
continue;
// If we're storing the same value back to a pointer that we just
// loaded from, then the store can be removed.
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
@ -287,23 +239,41 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
}
}
}
if (!InstDep.isDef()) {
// If this is a may-aliased store that is clobbering the store value, we
// can keep searching past it for another must-aliased pointer that stores
// to the same location. For example, in:
// store -> P
// store -> Q
// store -> P
// we can remove the first store to P even though we don't know if P and Q
// alias.
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
AliasAnalysis::Location Loc =
getAnalysis<AliasAnalysis>().getLocation(SI);
while (InstDep.isClobber() && isa<StoreInst>(InstDep.getInst()) &&
InstDep.getInst() != &BB.front())
InstDep = MD.getPointerDependencyFrom(Loc, false, InstDep.getInst(),
&BB);
}
}
// If this is a lifetime end marker, we can throw away the store.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(InstDep.getInst())) {
if (II->getIntrinsicID() == Intrinsic::lifetime_end) {
// If this is a store-store dependence, then the previous store is dead so
// long as this store is at least as big as it.
if (InstDep.isDef() && doesClobberMemory(InstDep.getInst())) {
Instruction *DepStore = InstDep.getInst();
if (isStoreAtLeastAsWideAs(Inst, DepStore, TD) && isElidable(DepStore)) {
// Delete the store and now-dead instructions that feed it.
// DeleteDeadInstruction can delete the current instruction. Save BBI
// in case we need it.
WeakVH NextInst(BBI);
DeleteDeadInstruction(Inst);
if (NextInst == 0) // Next instruction deleted.
BBI = BB.begin();
else if (BBI != BB.begin()) // Revisit this instruction if possible.
--BBI;
DeleteDeadInstruction(DepStore);
++NumFastStores;
MadeChange = true;
// DeleteDeadInstruction can delete the current instruction in loop
// cases, reset BBI.
BBI = Inst;
if (BBI != BB.begin())
--BBI;
continue;
}
}