[llvm] de63e4f - [Verifier] Reject elementwise atomicrmw with sub-byte element type (#213753)

[via llvm-commits]

Author: Yonah Goldberg
Date: 2026-08-04T08:27:39-07:00
New Revision: de63e4f3538ade12b5264e6e3f4682201ada16e8

URL: https://github.com/llvm/llvm-project/commit/de63e4f3538ade12b5264e6e3f4682201ada16e8
DIFF: https://github.com/llvm/llvm-project/commit/de63e4f3538ade12b5264e6e3f4682201ada16e8.diff

LOG: [Verifier] Reject elementwise atomicrmw with sub-byte element type (#213753)

In https://github.com/llvm/llvm-project/pull/208510/ I accidentally
introduced a bug where I allowed sub-byte element types with atomicrmw
elementwise (i.e. `<8 x i1>`).

The LangRef states:

```
The access type
must then be a fixed vector type whose total bit width is a power of two and
whose element type is supported by the corresponding scalar atomic instruction.
```

The second part of this sentence rejects sub-byte element types.

The fix is that elementwise atomics need to additionally call
`checkAtomicMemAccessSize` on the vector element type (they already call
it on the whole vector).

Added: 
    

Modified: 
    llvm/lib/IR/Verifier.cpp
    llvm/test/Assembler/invalid-atomicrmw-elementwise.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 0aa1ef4faebc1..1c2b716fefd7e 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -4768,6 +4768,8 @@ void Verifier::visitAtomicRMWInst(AtomicRMWInst &RMWI) {
     auto *VecTy = dyn_cast<FixedVectorType>(ElTy);
     Check(VecTy, "atomicrmw elementwise operand must have fixed vector type!",
           &RMWI, ElTy);
+    if (VecTy)
+      checkAtomicMemAccessSize(VecTy->getElementType(), &RMWI);
   }
 
   if (Op == AtomicRMWInst::Xchg) {

diff  --git a/llvm/test/Assembler/invalid-atomicrmw-elementwise.ll b/llvm/test/Assembler/invalid-atomicrmw-elementwise.ll
index 3c134cbb3b8c2..bfc6f104a2fc3 100644
--- a/llvm/test/Assembler/invalid-atomicrmw-elementwise.ll
+++ b/llvm/test/Assembler/invalid-atomicrmw-elementwise.ll
@@ -1,6 +1,8 @@
 ; RUN: split-file %s %t
 ; RUN: not llvm-as -disable-output %t/scalar.ll              2>&1 | FileCheck %t/scalar.ll
 ; RUN: not llvm-as -disable-output %t/odd-sized.ll           2>&1 | FileCheck %t/odd-sized.ll
+; RUN: not llvm-as -disable-output %t/non-byte.ll            2>&1 | FileCheck %t/non-byte.ll
+; RUN: not llvm-as -disable-output %t/non-byte-element.ll    2>&1 | FileCheck %t/non-byte-element.ll
 ; RUN: not llvm-as -disable-output %t/add-must-be-integer.ll 2>&1 | FileCheck %t/add-must-be-integer.ll
 ; RUN: not llvm-as -disable-output %t/fadd-must-be-fp.ll     2>&1 | FileCheck %t/fadd-must-be-fp.ll
 ; RUN: not llvm-as -disable-output %t/seq-cst.ll             2>&1 | FileCheck %t/seq-cst.ll
@@ -19,6 +21,20 @@ define <5 x i32> @bad_odd_sized_vector(ptr %p, <5 x i32> %v) {
   ret <5 x i32> %old
 }
 
+;--- non-byte.ll
+; CHECK: atomic memory access' size must be byte-sized
+define <4 x i1> @bad_non_byte(ptr %p, <4 x i1> %v) {
+  %old = atomicrmw elementwise xchg ptr %p, <4 x i1> %v monotonic, align 1
+  ret <4 x i1> %old
+}
+
+;--- non-byte-element.ll
+; CHECK: atomic memory access' size must be byte-sized
+define <8 x i1> @bad_non_byte_element(ptr %p, <8 x i1> %v) {
+  %old = atomicrmw elementwise xchg ptr %p, <8 x i1> %v monotonic, align 1
+  ret <8 x i1> %old
+}
+
 ;--- add-must-be-integer.ll
 ; CHECK: atomicrmw add operand must be an integer or fixed vector of integer type
 define <4 x float> @bad_add(ptr %p, <4 x float> %v) {