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

[Joseph Huber via libcxx-commits]

https://github.com/jhuber6 updated https://github.com/llvm/llvm-project/pull/101747

>From be681d36302900b67e02b4b87507e9b6aec2a8e2 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Fri, 2 Aug 2024 14:00:42 -0500
Subject: [PATCH 1/2] [libc] Adjust inline assembly constraints for the AMDGPU
 target

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.
---
 libcxx/test/support/test_macros.h | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/libcxx/test/support/test_macros.h b/libcxx/test/support/test_macros.h
index 15fc5b69b5207..d05d580826fe2 100644
--- a/libcxx/test/support/test_macros.h
+++ b/libcxx/test/support/test_macros.h
@@ -291,17 +291,27 @@ 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 as well
+  // as i8 / i1 arguments, so we just capture the pointer instead.
+#  if defined(__AMDGPU__)
+  Tp *tmp = &value;
+  asm volatile("" : "+v"(tmp) : : "memory");
+#  elif defined(__clang__)
   asm volatile("" : "+r,m"(value) : : "memory");
-#else
+#  else
   asm volatile("" : "+m,r"(value) : : "memory");
-#endif
+#  endif
   return value;
 }
 #else

>From 927a2d7d27dabc3084f6ca9bd1780a57327f8794 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Mon, 5 Aug 2024 11:43:46 -0500
Subject: [PATCH 2/2] Update test_macros.h

---
 libcxx/test/support/test_macros.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libcxx/test/support/test_macros.h b/libcxx/test/support/test_macros.h
index d05d580826fe2..e96208c85d1d2 100644
--- a/libcxx/test/support/test_macros.h
+++ b/libcxx/test/support/test_macros.h
@@ -305,7 +305,7 @@ inline Tp& DoNotOptimize(Tp& value) {
   // The `m` and `r` output constraint is invalid in the AMDGPU backend as well
   // as i8 / i1 arguments, so we just capture the pointer instead.
 #  if defined(__AMDGPU__)
-  Tp *tmp = &value;
+  Tp* tmp = &value;
   asm volatile("" : "+v"(tmp) : : "memory");
 #  elif defined(__clang__)
   asm volatile("" : "+r,m"(value) : : "memory");