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Teach memdep to use pointsToConstantMemory to determine that loads

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from constant memory don't alias any stores.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117636 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-10-29 01:14:04 +00:00
parent 1cfb043901
commit cd5c123a1d
2 changed files with 33 additions and 5 deletions
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15
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -161,8 +161,9 @@ getCallSiteDependencyFrom(CallSite CS, bool isReadOnlyCall,
}
/// getPointerDependencyFrom - Return the instruction on which a memory
/// location depends. If isLoad is true, this routine ignore may-aliases with
/// read-only operations.
/// 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.
MemDepResult MemoryDependenceAnalysis::
getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
BasicBlock::iterator ScanIt, BasicBlock *BB) {
@ -225,17 +226,21 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
Value *Pointer = LI->getPointerOperand();
uint64_t PointerSize = AA->getTypeStoreSize(LI->getType());
MDNode *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa);
AliasAnalysis::Location LoadLoc(Pointer, PointerSize, TBAATag);
// If we found a pointer, check if it could be the same as our pointer.
AliasAnalysis::AliasResult R =
AA->alias(AliasAnalysis::Location(Pointer, PointerSize, TBAATag),
MemLoc);
AliasAnalysis::AliasResult R = AA->alias(LoadLoc, MemLoc);
if (R == AliasAnalysis::NoAlias)
continue;
// May-alias loads don't depend on each other without a dependence.
if (isLoad && R == AliasAnalysis::MayAlias)
continue;
// Stores don't alias loads from read-only memory.
if (!isLoad && AA->pointsToConstantMemory(LoadLoc))
continue;
// Stores depend on may and must aliased loads, loads depend on must-alias
// loads.
return MemDepResult::getDef(Inst);

23
test/Analysis/TypeBasedAliasAnalysis/dse.ll
View File

@ -25,6 +25,29 @@ define i8 @test0_no(i8* %a, i8* %b) nounwind {
ret i8 %y
}
; CHECK: @test1_yes
; CHECK-NEXT: load i8* %b
; CHECK-NEXT: store i8 1, i8* %a
; CHECK-NEXT: ret i8 %y
define i8 @test1_yes(i8* %a, i8* %b) nounwind {
store i8 0, i8* %a
%y = load i8* %b, !tbaa !5
store i8 1, i8* %a
ret i8 %y
}
; CHECK: @test1_no
; CHECK-NEXT: store i8 0, i8* %a
; CHECK-NEXT: load i8* %b
; CHECK-NEXT: store i8 1, i8* %a
; CHECK-NEXT: ret i8 %y
define i8 @test1_no(i8* %a, i8* %b) nounwind {
store i8 0, i8* %a
%y = load i8* %b, !tbaa !6
store i8 1, i8* %a
ret i8 %y
}
; Root note.
!0 = metadata !{ }
; Some type.