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implement PR8576, deleting dead stores with intervening may-alias stores.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119927 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-11-21 07:34:32 +00:00
parent b7dfb970e6
commit f6f1f062cc
4 changed files with 42 additions and 6 deletions
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10
include/llvm/Analysis/MemoryDependenceAnalysis.h
View File

@ -335,11 +335,19 @@ namespace llvm {
/// critical edges.
void invalidateCachedPredecessors();
private:
/// getPointerDependencyFrom - Return the instruction on which a memory
/// location depends. If isLoad is true, this routine ignores may-aliases
/// with read-only operations. If isLoad is false, this routine ignores
/// may-aliases with reads from read-only locations.
///
/// Note that this is an uncached query, and thus may be inefficient.
///
MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc,
bool isLoad,
BasicBlock::iterator ScanIt,
BasicBlock *BB);
private:
MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
BasicBlock::iterator ScanIt,
BasicBlock *BB);

4
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -409,9 +409,9 @@ MemDepResult MemoryDependenceAnalysis::getDependency(Instruction *QueryInst) {
if (MemLoc.Ptr) {
// If we can do a pointer scan, make it happen.
bool isLoad = !(MR & AliasAnalysis::Mod);
if (IntrinsicInst *II = dyn_cast<MemoryUseIntrinsic>(QueryInst)) {
if (IntrinsicInst *II = dyn_cast<MemoryUseIntrinsic>(QueryInst))
isLoad |= II->getIntrinsicID() == Intrinsic::lifetime_end;
}
LocalCache = getPointerDependencyFrom(MemLoc, isLoad, ScanPos,
QueryParent);
} else if (isa<CallInst>(QueryInst) || isa<InvokeInst>(QueryInst)) {

25
lib/Transforms/Scalar/DeadStoreElimination.cpp
View File

@ -217,9 +217,28 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
continue;
}
// If not a definite must-alias dependency, ignore it.
if (!InstDep.isDef())
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 dependency, ignore it.
if (!InstDep.isDef())
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.

9
test/Transforms/DeadStoreElimination/simple.ll
View File

@ -11,3 +11,12 @@ define void @test1(i32* %Q, i32* %P) {
; CHECK-NEXT: ret void
}
; PR8576 - Should delete store of 10 even though p/q are may aliases.
define void @test2(i32 *%p, i32 *%q) {
store i32 10, i32* %p, align 4
store i32 20, i32* %q, align 4
store i32 30, i32* %p, align 4
ret void
; CHECK: @test2
; CHECK-NEXT: store i32 20
}