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[LLVM][MemCpyOpt] Unify alias tags if we optimize allocas #129537

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Merged
merged 10 commits into from
Apr 10, 2025
Merged

[LLVM][MemCpyOpt] Unify alias tags if we optimize allocas #129537

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4c49512
[LLVM][MemCpyOpt] Unify alias tags if we optimize allocas
DominikAdamski Feb 24, 2025
5e04c39
Simplified test
DominikAdamski Mar 3, 2025
dddcc8a
Fix style
DominikAdamski Mar 18, 2025
ae4139a
Fix style
DominikAdamski Mar 18, 2025
3ab8a71
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DominikAdamski Mar 18, 2025
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DominikAdamski Mar 21, 2025
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DominikAdamski Apr 7, 2025
7fc13ac
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DominikAdamski Apr 8, 2025
2f00aa7
Remove alias.scope
DominikAdamski Apr 8, 2025
92584ea
Merge branch 'main' into fix_memcpy_tbaa_tags
DominikAdamski Apr 8, 2025
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16 changes: 12 additions & 4 deletions llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1569,6 +1569,10 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
continue;
}
}
if (UI->hasMetadata(LLVMContext::MD_tbaa))
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@nikic nikic Apr 7, 2025

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I'd combine these checks with ||, no need to repeat the insert thrice.

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@DominikAdamski DominikAdamski Apr 8, 2025

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Done, I merged main branch and I simplified collection of instructions.

NoAliasInstrs.insert(UI);
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@nikic nikic Apr 7, 2025

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Now that this no longer holds only !noalias, rename to AAMetadataInstrs or something?

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@nikic nikic Apr 7, 2025

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Though at this point it would probably make sense to just collect all instructions here (regardless of whether they have metadata) and call setMetadata on all of them, so we don't have to list the MD kinds twice.

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@DominikAdamski DominikAdamski Apr 8, 2025

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Done, I just collect all instructions here

if (UI->hasMetadata(LLVMContext::MD_tbaa_struct))
NoAliasInstrs.insert(UI);
if (UI->hasMetadata(LLVMContext::MD_noalias))
NoAliasInstrs.insert(UI);
if (!ModRefCallback(UI))
Expand Down Expand Up @@ -1675,11 +1679,15 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
}

// As this transformation can cause memory accesses that didn't previously
// alias to begin to alias one another, we remove !noalias metadata from any
// uses of either alloca. This is conservative, but more precision doesn't
// seem worthwhile right now.
for (Instruction *I : NoAliasInstrs)
// alias to begin to alias one another, we remove !noalias, !tbaa
// and !tbaa_struct metadata from any uses of either alloca.
// This is conservative, but more precision doesn't seem worthwhile
// right now.
for (Instruction *I : NoAliasInstrs) {
I->setMetadata(LLVMContext::MD_noalias, nullptr);
I->setMetadata(LLVMContext::MD_tbaa, nullptr);
I->setMetadata(LLVMContext::MD_tbaa_struct, nullptr);
}

LLVM_DEBUG(dbgs() << "Stack Move: Performed staack-move optimization\n");
NumStackMove++;
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77 changes: 77 additions & 0 deletions llvm/test/Transforms/MemCpyOpt/memcpy-tbaa.ll
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@nikic nikic Mar 18, 2025

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This test still doesn't look minimal. Wouldn't it be sufficient to have a store with one tbaa tag, a memcpy and a load with another tag?

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@DominikAdamski DominikAdamski Mar 21, 2025

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I removed unnecessary instructions.

Original file line number Diff line number Diff line change
@@ -0,0 +1,77 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt < %s -passes=memcpyopt,dse -S -verify-memoryssa | FileCheck %s

define void @test() local_unnamed_addr {
; CHECK-LABEL: define void @test() local_unnamed_addr {
; CHECK-NEXT: [[TEST_ARRAY_B:%.*]] = alloca [31 x float], align 4
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr float, ptr [[TEST_ARRAY_B]], i64 1
; CHECK-NEXT: store float 0x3E6AA51880000000, ptr [[TMP1]], align 4
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr float, ptr [[TEST_ARRAY_B]], i64 1
; CHECK-NEXT: [[TMP3:%.*]] = load float, ptr [[TMP2]], align 4
; CHECK-NEXT: ret void
;
%test_array_a = alloca [31 x float], align 4
%test_array_b = alloca [31 x float], align 4
%1 = getelementptr float, ptr %test_array_b, i64 1
store float 0x3E6AA51880000000, ptr %1, align 4, !tbaa !4
call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 4 dereferenceable(124) %test_array_a, ptr noundef nonnull align 4 dereferenceable(124) %test_array_b, i64 124, i1 false)
%2 = getelementptr float, ptr %test_array_a, i64 1
%3 = load float, ptr %2, align 4, !tbaa !7
ret void
}

%struct.Outer = type { float, double, %struct.Inner }
%struct.Inner = type { i32, float }

; Function Attrs: nounwind uwtable
define dso_local float @f() {
; CHECK-LABEL: define dso_local float @f() {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[TEST1:%.*]] = alloca [[STRUCT_OUTER:%.*]], align 8
; CHECK-NEXT: [[F:%.*]] = getelementptr inbounds nuw [[STRUCT_OUTER]], ptr [[TEST1]], i32 0, i32 0
; CHECK-NEXT: store float 0.000000e+00, ptr [[F]], align 8
; CHECK-NEXT: [[F1:%.*]] = getelementptr inbounds nuw [[STRUCT_OUTER]], ptr [[TEST1]], i32 0, i32 0
; CHECK-NEXT: [[TMP0:%.*]] = load float, ptr [[F1]], align 8
; CHECK-NEXT: [[ADD:%.*]] = fadd float [[TMP0]], 2.000000e+00
; CHECK-NEXT: store float [[ADD]], ptr [[F1]], align 8
; CHECK-NEXT: [[F2:%.*]] = getelementptr inbounds nuw [[STRUCT_OUTER]], ptr [[TEST1]], i32 0, i32 0
; CHECK-NEXT: [[TMP1:%.*]] = load float, ptr [[F2]], align 8
; CHECK-NEXT: ret float [[TMP1]]
;
entry:
%test = alloca %struct.Outer, align 8
%test1 = alloca %struct.Outer, align 8
%f = getelementptr inbounds nuw %struct.Outer, ptr %test1, i32 0, i32 0
store float 0.000000e+00, ptr %f, align 8, !tbaa !9
%inner_a = getelementptr inbounds nuw %struct.Outer, ptr %test1, i32 0, i32 2
%i = getelementptr inbounds nuw %struct.Inner, ptr %inner_a, i32 0, i32 0
store i32 0, ptr %i, align 8, !tbaa !17
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %test, ptr align 8 %test1, i64 24, i1 false)
%f1 = getelementptr inbounds nuw %struct.Outer, ptr %test, i32 0, i32 0
%0 = load float, ptr %f1, align 8, !tbaa !9
%add = fadd float %0, 2.000000e+00
store float %add, ptr %f1, align 8, !tbaa !9
%f2 = getelementptr inbounds nuw %struct.Outer, ptr %test, i32 0, i32 0
%1 = load float, ptr %f2, align 8, !tbaa !9
ret float %1
}

!1 = !{!"any data access", !2, i64 0}
!2 = !{!"any access", !3, i64 0}
!3 = !{!"Flang function root test"}
!4 = !{!5, !5, i64 0}
!5 = !{!"allocated data/test_array_a", !6, i64 0}
!6 = !{!"allocated data", !1, i64 0}
!7 = !{!8, !8, i64 0}
!8 = !{!"allocated data/test_array_b", !6, i64 0}
!9 = !{!10, !11, i64 0}
!10 = !{!"Outer", !11, i64 0, !14, i64 8, !15, i64 16}
!11 = !{!"float", !12, i64 0}
!12 = !{!"omnipotent char", !13, i64 0}
!13 = !{!"Simple C/C++ TBAA"}
!14 = !{!"double", !12, i64 0}
!15 = !{!"Inner", !16, i64 0, !11, i64 4}
!16 = !{!"int", !12, i64 0}
!17 = !{!10, !16, i64 16}