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[InstCombine] Read-only call without return can capture #157878

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Merged
merged 1 commit into from
Sep 15, 2025
Merged

[InstCombine] Read-only call without return can capture #157878

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4 changes: 2 additions & 2 deletions llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -107,8 +107,8 @@ isOnlyCopiedFromConstantMemory(AAResults *AA, AllocaInst *V,
// a load (but one that potentially returns the value itself), so we can
// ignore it if we know that the value isn't captured.
bool NoCapture = Call->doesNotCapture(DataOpNo);
if ((Call->onlyReadsMemory() && (Call->use_empty() || NoCapture)) ||
(Call->onlyReadsMemory(DataOpNo) && NoCapture))
if (NoCapture &&
(Call->onlyReadsMemory() || Call->onlyReadsMemory(DataOpNo)))
continue;
}

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27 changes: 21 additions & 6 deletions llvm/test/Transforms/InstCombine/memcpy-from-global.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -139,13 +139,14 @@ define void @test2_addrspacecast() {
ret void
}

declare void @bar(ptr)
declare void @bar_as1(ptr addrspace(1))
declare void @bar(ptr nocapture)
declare void @bar_may_capture(ptr)
declare void @bar_as1(ptr addrspace(1) nocapture)


;; Should be able to eliminate the alloca.
define void @test3() {
; CHECK-LABEL: @test3(
define void @test3_nocapture() {
; CHECK-LABEL: @test3_nocapture(
; CHECK-NEXT: call void @bar(ptr nonnull @G) #[[ATTR3:[0-9]+]]
; CHECK-NEXT: ret void
;
Expand All @@ -155,6 +156,20 @@ define void @test3() {
ret void
}

; Can not eliminate the alloca, as the function may capture its address.
define void @test3_may_capture() {
; CHECK-LABEL: @test3_may_capture(
; CHECK-NEXT: [[A:%.*]] = alloca [[T:%.*]], align 8
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 8 dereferenceable(124) [[A]], ptr noundef nonnull align 16 dereferenceable(124) @G, i64 124, i1 false)
; CHECK-NEXT: call void @bar_may_capture(ptr nonnull [[A]]) #[[ATTR3]]
; CHECK-NEXT: ret void
;
%A = alloca %T
call void @llvm.memcpy.p0.p0.i64(ptr align 4 %A, ptr align 4 @G, i64 124, i1 false)
call void @bar_may_capture(ptr %A) readonly
ret void
}

define void @test3_addrspacecast() {
; CHECK-LABEL: @test3_addrspacecast(
; CHECK-NEXT: call void @bar(ptr nonnull @G) #[[ATTR3]]
Expand Down Expand Up @@ -395,12 +410,12 @@ define void @memcpy_to_capturing_readonly() {
; CHECK-LABEL: @memcpy_to_capturing_readonly(
; CHECK-NEXT: [[A:%.*]] = alloca [[U:%.*]], align 16
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 16 dereferenceable(20) [[A]], ptr noundef nonnull align 16 dereferenceable(20) @H, i64 20, i1 false)
; CHECK-NEXT: call void @bar(ptr nonnull readonly [[A]])
; CHECK-NEXT: call void @bar_may_capture(ptr nonnull readonly [[A]])
; CHECK-NEXT: ret void
;
%A = alloca %U, align 16
call void @llvm.memcpy.p0.p0.i64(ptr align 4 %A, ptr align 4 @H, i64 20, i1 false)
call void @bar(ptr readonly %A)
call void @bar_may_capture(ptr readonly %A)
ret void
}

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