[libcxx-commits] [libcxx] [libc] Adjust inline assembly constraints for the AMDGPU target (PR #101747)

[via libcxx-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Joseph Huber (jhuber6)

<details>
<summary>Changes</summary>

Summary:
These assembly constraints are illegal / invalid on the AMDGPU target.
The `r` constraint is only valid on inputs and the `m` constraint isn't
accepted at all. The NVPTX target can handle them because it uses a more
permissive virtual machine (PTX is an IR). Simply add exceptions on the
target to make these work.


---
Full diff: https://github.com/llvm/llvm-project/pull/101747.diff


1 Files Affected:

- (modified) libcxx/test/support/test_macros.h (+13-5) 


``````````diff
diff --git a/libcxx/test/support/test_macros.h b/libcxx/test/support/test_macros.h
index 15fc5b69b5207..65037d03b9567 100644
--- a/libcxx/test/support/test_macros.h
+++ b/libcxx/test/support/test_macros.h
@@ -291,17 +291,25 @@ struct is_same<T, T> { enum {value = 1}; };
 // when optimizations are enabled.
 template <class Tp>
 inline Tp const& DoNotOptimize(Tp const& value) {
-    asm volatile("" : : "r,m"(value) : "memory");
-    return value;
+  // The `m` constraint is invalid in the AMDGPU backend.
+#  if defined(__AMDGPU__) || defined(__NVPTX__)
+  asm volatile("" : : "r"(value) : "memory");
+#  else
+  asm volatile("" : : "r,m"(value) : "memory");
+#  endif
+  return value;
 }
 
 template <class Tp>
 inline Tp& DoNotOptimize(Tp& value) {
-#if defined(__clang__)
+  // The `m` and `r` output constraint is invalid in the AMDGPU backend.
+#  if defined(__AMDGPU__)
+  asm volatile("" : "+v"(value) : : "memory");
+#  elif defined(__clang__)
   asm volatile("" : "+r,m"(value) : : "memory");
-#else
+#  else
   asm volatile("" : "+m,r"(value) : : "memory");
-#endif
+#  endif
   return value;
 }
 #else

``````````

</details>


https://github.com/llvm/llvm-project/pull/101747