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Teach BasicAA that a constant expression can't alias memory provably not

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allocated until runtime (such as an alloca). Patch by Hans Wennborg!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88760 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2009-11-14 06:15:14 +00:00
parent fae3e92345
commit 20162ac566
2 changed files with 45 additions and 1 deletions
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7
lib/Analysis/BasicAliasAnalysis.cpp
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@ -659,7 +659,12 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
// If V1/V2 point to two different objects we know that we have no alias.
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
return NoAlias;
// Constant pointers can't alias with non-const isIdentifiedObject objects.
if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
(isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
return NoAlias;
// Arguments can't alias with local allocations or noalias calls.
if ((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
(isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1))))

39
test/Transforms/DeadStoreElimination/const-pointers.ll Normal file
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@ -0,0 +1,39 @@
; RUN: opt %s -dse -S | FileCheck %s
%t = type { i32 }
@g = global i32 42;
define void @test1(%t* noalias %pp) {
%p = getelementptr inbounds %t* %pp, i32 0, i32 0
store i32 1, i32* %p; <-- This is dead
%x = load i32* inttoptr (i32 12345 to i32*)
store i32 %x, i32* %p
ret void
; CHECK define void @test1
; CHECK: store
; CHECK-NOT: store
; CHECK: ret void
}
define void @test3() {
store i32 1, i32* @g; <-- This is dead.
store i32 42, i32* @g
ret void
;CHECK define void @test3
;CHECK: store
;CHECK-NOT: store
;CHECK: ret void
}
define void @test4(i32* %p) {
store i32 1, i32* %p
%x = load i32* @g; <-- %p and @g could alias
store i32 %x, i32* %p
ret void
; CHECK define void @test4
; CHECK: store
; CHECK: store
; CHECK: ret void
}