[compiler-rt] [AArch64][SME] Fix broken compiler check for SME2 support in compiler-rt (PR #121625)

[Amara Emerson via llvm-commits]

https://github.com/aemerson created https://github.com/llvm/llvm-project/pull/121625

This compile time test uses inline asm with `.arch` directives to set the target feature. It is however broken and always fails, since each `asm()` construct in LLVM sets up a new AsmParser, and therefore the `.arch` directive has no effect on later `asm()` contents. To fix this we need to use a single inline `asm()` call with the entire code chunk to emit contained inside.

>From e0b121ce26bb3146f7336325f33ce3070eaa6b0c Mon Sep 17 00:00:00 2001
From: Amara Emerson <amara at apple.com>
Date: Fri, 3 Jan 2025 22:01:34 -0800
Subject: [PATCH] [AArch64][SME] Fix broken compiler check for SME2 support in
 compiler-rt.

This compile time test uses inline asm with .arch directives to set the
target feature. It is however broken and always fails, since each asm()
construct in LLVM sets up a new AsmParser, and therefore the .arch directive
has no effect on later asm() contents. To fix this we need to use a single
inline asm() call with the entire code chunk to emit contained inside.
---
 compiler-rt/cmake/builtin-config-ix.cmake | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/compiler-rt/cmake/builtin-config-ix.cmake b/compiler-rt/cmake/builtin-config-ix.cmake
index 706a1ff7eeb6db..b1bde47ec8555f 100644
--- a/compiler-rt/cmake/builtin-config-ix.cmake
+++ b/compiler-rt/cmake/builtin-config-ix.cmake
@@ -43,9 +43,9 @@ asm(\"cas w0, w1, [x2]\");
 builtin_check_c_compiler_source(COMPILER_RT_HAS_AARCH64_SME
 "
 void foo(void)  __arm_streaming_compatible {
-  asm(\".arch armv9-a+sme2\");
-  asm(\"smstart\");
-  asm(\"ldr zt0, [sp]\");
+  asm(\".arch armv9-a+sme2\\n\"
+      \"smstart\\n\"
+      \"ldr zt0, [sp]\");
 }
 ")