[llvm] [AtomicExpand] Preserve AA metadata when rewriting atomic operations (PR #206418)
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Thu Jul 9 02:41:25 PDT 2026
https://github.com/ayrai-gb updated https://github.com/llvm/llvm-project/pull/206418
>From a112c723153bb4120af715d9bd367ca666fd513c Mon Sep 17 00:00:00 2001
From: Ayush Rai <your-email at amd.com>
Date: Mon, 29 Jun 2026 11:30:03 +0530
Subject: [PATCH 1/3] [AtomicExpand] Preserve AA metadata in
expandPartwordCmpXchg
---
llvm/lib/CodeGen/AtomicExpandPass.cpp | 2 ++
.../partword-cmpxchg-preserve-metadata.ll | 22 +++++++++++++++++++
2 files changed, 24 insertions(+)
create mode 100644 llvm/test/Transforms/AtomicExpand/AMDGPU/partword-cmpxchg-preserve-metadata.ll
diff --git a/llvm/lib/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index 059c0d5cb7b8b..fc34760f36532 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -1251,6 +1251,7 @@ bool AtomicExpandImpl::expandPartwordCmpXchg(AtomicCmpXchgInst *CI) {
// addIncoming is done first so that any replaceAllUsesWith calls during
// normalization correctly update the PHI incoming value.
InitLoaded->setVolatile(CI->isVolatile());
+ copyMetadataForAtomic(*InitLoaded, *CI);
if (TLI->shouldIssueAtomicLoadForAtomicEmulationLoop()) {
InitLoaded->setAtomic(AtomicOrdering::Monotonic, CI->getSyncScopeID());
// The newly created load might need to be lowered further. Because it is
@@ -1272,6 +1273,7 @@ bool AtomicExpandImpl::expandPartwordCmpXchg(AtomicCmpXchgInst *CI) {
// expecting the underlying cmpxchg to be a machine instruction,
// which is strong anyways.
NewCI->setWeak(CI->isWeak());
+ copyMetadataForAtomic(*NewCI, *CI);
Value *OldVal = Builder.CreateExtractValue(NewCI, 0);
Value *Success = Builder.CreateExtractValue(NewCI, 1);
diff --git a/llvm/test/Transforms/AtomicExpand/AMDGPU/partword-cmpxchg-preserve-metadata.ll b/llvm/test/Transforms/AtomicExpand/AMDGPU/partword-cmpxchg-preserve-metadata.ll
new file mode 100644
index 0000000000000..5bbb04a555129
--- /dev/null
+++ b/llvm/test/Transforms/AtomicExpand/AMDGPU/partword-cmpxchg-preserve-metadata.ll
@@ -0,0 +1,22 @@
+; RUN: opt -mtriple=amdgcn-amd-amdhsa -S -passes='require<libcall-lowering-info>,atomic-expand' %s | FileCheck %s
+
+; A sub-word (i16) cmpxchg is widened to a word-sized cmpxchg retry loop by
+; expandPartwordCmpXchg. Both the seed load (InitLoaded) and the widened cmpxchg
+; must preserve the original !tbaa/!noalias metadata, matching the sibling
+; widenPartwordAtomicRMW path.
+
+define { i16, i1 } @test_cmpxchg_i16_preserves_metadata(ptr %p, i16 %cmp, i16 %new) {
+; CHECK-LABEL: @test_cmpxchg_i16_preserves_metadata(
+; CHECK: load i32, ptr {{%.*}}, align 4{{.*}}!tbaa ![[TBAA:[0-9]+]]{{.*}}!noalias ![[NOALIAS:[0-9]+]]
+; CHECK: cmpxchg ptr {{%.*}} seq_cst seq_cst, align 4{{.*}}!tbaa ![[TBAA]]{{.*}}!noalias ![[NOALIAS]]
+ %r = cmpxchg ptr %p, i16 %cmp, i16 %new seq_cst seq_cst, align 2, !tbaa !2, !noalias !6
+ ret { i16, i1 } %r
+}
+
+!0 = !{!"alias-domain"}
+!1 = !{!"alias-scope-a", !0}
+!2 = !{!3, !3, i64 0}
+!3 = !{!"int", !4, i64 0}
+!4 = !{!"omnipotent char", !5, i64 0}
+!5 = !{!"Simple C/C++ TBAA"}
+!6 = !{!1}
>From e5dcd198b3d6bd49d093cd1dec88d04f70f8827e Mon Sep 17 00:00:00 2001
From: Ayush Rai <your-email at amd.com>
Date: Mon, 29 Jun 2026 12:12:17 +0530
Subject: [PATCH 2/3] [AtomicExpand] Preserve AA metadata when casting atomics
to integer
---
llvm/lib/CodeGen/AtomicExpandPass.cpp | 4 ++
...tomic-cast-to-integer-preserve-metadata.ll | 46 +++++++++++++++++++
2 files changed, 50 insertions(+)
create mode 100644 llvm/test/Transforms/AtomicExpand/X86/atomic-cast-to-integer-preserve-metadata.ll
diff --git a/llvm/lib/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index fc34760f36532..5ebbe1172f439 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -567,6 +567,7 @@ LoadInst *AtomicExpandImpl::convertAtomicLoadToIntegerType(LoadInst *LI) {
NewLI->setAlignment(LI->getAlign());
NewLI->setVolatile(LI->isVolatile());
NewLI->setAtomic(LI->getOrdering(), LI->getSyncScopeID());
+ copyMetadataForAtomic(*NewLI, *LI);
LLVM_DEBUG(dbgs() << "Replaced " << *LI << " with " << *NewLI << "\n");
Value *NewVal = LI->getType()->isPtrOrPtrVectorTy()
@@ -690,6 +691,7 @@ bool AtomicExpandImpl::expandAtomicLoadToCmpXchg(LoadInst *LI) {
AtomicCmpXchgInst::getStrongestFailureOrdering(Order),
LI->getSyncScopeID());
Pair->setVolatile(LI->isVolatile());
+ copyMetadataForAtomic(*Pair, *LI);
Value *Loaded = Builder.CreateExtractValue(Pair, 0, "loaded");
if (NeedBitcast)
Loaded = Builder.CreateBitCast(Loaded, Ty);
@@ -723,6 +725,7 @@ StoreInst *AtomicExpandImpl::convertAtomicStoreToIntegerType(StoreInst *SI) {
NewSI->setAlignment(SI->getAlign());
NewSI->setVolatile(SI->isVolatile());
NewSI->setAtomic(SI->getOrdering(), SI->getSyncScopeID());
+ copyMetadataForAtomic(*NewSI, *SI);
LLVM_DEBUG(dbgs() << "Replaced " << *SI << " with " << *NewSI << "\n");
SI->eraseFromParent();
return NewSI;
@@ -1452,6 +1455,7 @@ AtomicExpandImpl::convertCmpXchgToIntegerType(AtomicCmpXchgInst *CI) {
CI->getFailureOrdering(), CI->getSyncScopeID());
NewCI->setVolatile(CI->isVolatile());
NewCI->setWeak(CI->isWeak());
+ copyMetadataForAtomic(*NewCI, *CI);
LLVM_DEBUG(dbgs() << "Replaced " << *CI << " with " << *NewCI << "\n");
Value *OldVal = Builder.CreateExtractValue(NewCI, 0);
diff --git a/llvm/test/Transforms/AtomicExpand/X86/atomic-cast-to-integer-preserve-metadata.ll b/llvm/test/Transforms/AtomicExpand/X86/atomic-cast-to-integer-preserve-metadata.ll
new file mode 100644
index 0000000000000..8564a0f73f08b
--- /dev/null
+++ b/llvm/test/Transforms/AtomicExpand/X86/atomic-cast-to-integer-preserve-metadata.ll
@@ -0,0 +1,46 @@
+; RUN: opt -S %s -passes='require<libcall-lowering-info>,atomic-expand' -mtriple=x86_64-linux-gnu | FileCheck %s
+; RUN: opt -S %s -passes='require<libcall-lowering-info>,atomic-expand' -mtriple=x86_64-linux-gnu -mattr=+cx16 | FileCheck %s --check-prefixes=CHECK,CX16
+
+; AtomicExpand casts float/vector/pointer atomics to integer atomics so the
+; backend can select them. The cast must preserve the original !tbaa/!noalias
+; metadata, matching the sibling convertAtomicXchgToIntegerType.
+
+; convertAtomicLoadToIntegerType
+define float @castload(ptr %p) {
+; CHECK-LABEL: define float @castload(
+; CHECK: load atomic i32, ptr {{%.*}} seq_cst, align 4, !tbaa ![[TBAA:[0-9]+]], !noalias ![[NOALIAS:[0-9]+]]
+ %r = load atomic float, ptr %p seq_cst, align 4, !tbaa !2, !noalias !6
+ ret float %r
+}
+
+; convertAtomicStoreToIntegerType
+define void @caststore(ptr %p, float %v) {
+; CHECK-LABEL: define void @caststore(
+; CHECK: store atomic i32 {{%.*}}, ptr {{%.*}} seq_cst, align 4, !tbaa ![[TBAA]], !noalias ![[NOALIAS]]
+ store atomic float %v, ptr %p seq_cst, align 4, !tbaa !2, !noalias !6
+ ret void
+}
+
+; convertCmpXchgToIntegerType (pointer cmpxchg cast to integer)
+define { ptr, i1 } @castcmpxchg(ptr %p, ptr %c, ptr %n) {
+; CHECK-LABEL: define { ptr, i1 } @castcmpxchg(
+; CHECK: cmpxchg ptr {{%.*}} seq_cst seq_cst, align 8, !tbaa ![[TBAA]], !noalias ![[NOALIAS]]
+ %r = cmpxchg ptr %p, ptr %c, ptr %n seq_cst seq_cst, align 8, !tbaa !2, !noalias !6
+ ret { ptr, i1 } %r
+}
+
+; expandAtomicLoadToCmpXchg (wide i128 load -> dummy cmpxchg, needs cx16)
+define i128 @load_cmpxchg(ptr %p) {
+; CX16-LABEL: define i128 @load_cmpxchg(
+; CX16: cmpxchg ptr {{%.*}}, i128 0, i128 0 seq_cst seq_cst, align 16, !tbaa ![[TBAA]], !noalias ![[NOALIAS]]
+ %r = load atomic i128, ptr %p seq_cst, align 16, !tbaa !2, !noalias !6
+ ret i128 %r
+}
+
+!0 = !{!"alias-domain"}
+!1 = !{!"alias-scope-a", !0}
+!2 = !{!3, !3, i64 0}
+!3 = !{!"int", !4, i64 0}
+!4 = !{!"omnipotent char", !5, i64 0}
+!5 = !{!"Simple C/C++ TBAA"}
+!6 = !{!1}
>From fbf43ea0b3569e32dd717818056627e8179f80c0 Mon Sep 17 00:00:00 2001
From: Ayush Rai <your-email at amd.com>
Date: Mon, 29 Jun 2026 12:47:57 +0530
Subject: [PATCH 3/3] [AtomicExpand] Preserve AA metadata on the seed load in
insertRMWCmpXchgLoop
---
llvm/lib/CodeGen/AtomicExpandPass.cpp | 2 ++
...tomicrmw-cmpxchg-loop-preserve-metadata.ll | 22 +++++++++++++++++++
2 files changed, 24 insertions(+)
create mode 100644 llvm/test/Transforms/AtomicExpand/X86/atomicrmw-cmpxchg-loop-preserve-metadata.ll
diff --git a/llvm/lib/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index 5ebbe1172f439..0a7033a0d15e9 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -1806,6 +1806,8 @@ Value *AtomicExpandImpl::insertRMWCmpXchgLoop(
// addIncoming is done first so that any replaceAllUsesWith calls during
// normalization correctly update the PHI incoming value.
InitLoaded->setVolatile(IsVolatile);
+ if (MetadataSrc)
+ copyMetadataForAtomic(*InitLoaded, *MetadataSrc);
if (TLI->shouldIssueAtomicLoadForAtomicEmulationLoop()) {
InitLoaded->setAtomic(AtomicOrdering::Monotonic, SSID);
// The newly created load might need to be lowered further. Because it is
diff --git a/llvm/test/Transforms/AtomicExpand/X86/atomicrmw-cmpxchg-loop-preserve-metadata.ll b/llvm/test/Transforms/AtomicExpand/X86/atomicrmw-cmpxchg-loop-preserve-metadata.ll
new file mode 100644
index 0000000000000..54aa87e6c42df
--- /dev/null
+++ b/llvm/test/Transforms/AtomicExpand/X86/atomicrmw-cmpxchg-loop-preserve-metadata.ll
@@ -0,0 +1,22 @@
+; RUN: opt -S %s -passes='require<libcall-lowering-info>,atomic-expand' -mtriple=x86_64-linux-gnu | FileCheck %s
+
+; An atomicrmw that has no native instruction (e.g. nand) is expanded to a
+; cmpxchg retry loop by insertRMWCmpXchgLoop. The pre-loop seed load
+; (InitLoaded) must preserve the original !tbaa/!noalias metadata, matching the
+; widened cmpxchg in the loop.
+
+define i32 @atomicrmw_nand_preserves_metadata(ptr %p, i32 %v) {
+; CHECK-LABEL: define i32 @atomicrmw_nand_preserves_metadata(
+; CHECK: load i32, ptr {{%.*}}, align 4, !tbaa ![[TBAA:[0-9]+]], !noalias ![[NOALIAS:[0-9]+]]
+; CHECK: cmpxchg ptr {{%.*}} seq_cst seq_cst, align 4, !tbaa ![[TBAA]], !noalias ![[NOALIAS]]
+ %r = atomicrmw nand ptr %p, i32 %v seq_cst, align 4, !tbaa !2, !noalias !6
+ ret i32 %r
+}
+
+!0 = !{!"alias-domain"}
+!1 = !{!"alias-scope-a", !0}
+!2 = !{!3, !3, i64 0}
+!3 = !{!"int", !4, i64 0}
+!4 = !{!"omnipotent char", !5, i64 0}
+!5 = !{!"Simple C/C++ TBAA"}
+!6 = !{!1}
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