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[DSE] Check for noalias calls rather than alloc functions

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For these "visible on unwind/ret" checks we only care about the
fact that no other code has access to the pointer (unless it
escapes). A noalias call is sufficient for this, it does not
have to be a known allocation function.

This is basically the same change as D116728, but for DSE rather
than LICM.
This commit is contained in:
Nikita Popov
2022-01-11 12:08:44 +01:00
parent ec016681d3
commit 3cef3cf02f
2 changed files with 2 additions and 6 deletions
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4
llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
View File

@@ -961,7 +961,7 @@ struct DSEState {
I.first->second = false;
} else {
auto *Inst = dyn_cast<Instruction>(V);
if (Inst && isAllocLikeFn(Inst, &TLI))
if (Inst && isNoAliasCall(Inst))
I.first->second = !PointerMayBeCaptured(V, true, false);
}
}
@@ -974,7 +974,7 @@ struct DSEState {
auto I = InvisibleToCallerBeforeRet.insert({V, false});
if (I.second) {
auto *Inst = dyn_cast<Instruction>(V);
if (Inst && isAllocLikeFn(Inst, &TLI))
if (Inst && isNoAliasCall(Inst))
// NOTE: This could be made more precise by PointerMayBeCapturedBefore
// with the killing MemoryDef. But we refrain from doing so for now to
// limit compile-time and this does not cause any changes to the number

4
llvm/test/Transforms/DeadStoreElimination/simple.ll
View File

@@ -229,9 +229,6 @@ define i32* @test_custom_malloc_no_escape_before_return() {
; CHECK-LABEL: @test_custom_malloc_no_escape_before_return(
; CHECK-NEXT: [[PTR:%.*]] = tail call i8* @custom_malloc(i32 4)
; CHECK-NEXT: [[P:%.*]] = bitcast i8* [[PTR]] to i32*
; CHECK-NEXT: [[DEAD:%.*]] = load i32, i32* [[P]], align 4
; CHECK-NEXT: [[DEAD2:%.*]] = add i32 [[DEAD]], 1
; CHECK-NEXT: store i32 [[DEAD2]], i32* [[P]], align 4
; CHECK-NEXT: call void @may_unwind()
; CHECK-NEXT: store i32 0, i32* [[P]], align 4
; CHECK-NEXT: ret i32* [[P]]
@@ -313,7 +310,6 @@ define void @malloc_no_escape() {
define void @custom_malloc_no_escape() {
; CHECK-LABEL: @custom_malloc_no_escape(
; CHECK-NEXT: [[M:%.*]] = call i8* @custom_malloc(i32 24)
; CHECK-NEXT: store i8 0, i8* [[M]], align 1
; CHECK-NEXT: ret void
;
%m = call i8* @custom_malloc(i32 24)