[gcc r14-4880] aarch64: Avoid bogus atomics match

[Richard Sandiford <rsandifo@gcc.gnu.org>]

https://gcc.gnu.org/g:b632a516a0448818a25f35e15a4bf0a3187af359

commit r14-4880-gb632a516a0448818a25f35e15a4bf0a3187af359
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Oct 24 10:58:40 2023 +0100

    aarch64: Avoid bogus atomics match
    
    The non-LSE pattern aarch64_atomic_exchange<mode> comes before the
    LSE pattern aarch64_atomic_exchange<mode>_lse.  From a recog
    perspective, the only difference between the patterns is that
    the non-LSE one clobbers CC and needs a scratch.
    
    However, combine and RTL-SSA can both add clobbers to make a
    pattern match.  This means that if they try to rerecognise an
    LSE pattern, they could end up turning it into a non-LSE pattern.
    This patch adds a !TARGET_LSE test to avoid that.
    
    This is needed to avoid a regression with later patches.
    
    gcc/
            * config/aarch64/atomics.md (aarch64_atomic_exchange<mode>): Require
            !TARGET_LSE.

Diff:
---
 gcc/config/aarch64/atomics.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/config/aarch64/atomics.md b/gcc/config/aarch64/atomics.md
index 2b6f04efa6c9..055a87320caa 100644
--- a/gcc/config/aarch64/atomics.md
+++ b/gcc/config/aarch64/atomics.md
@@ -224,7 +224,7 @@
       UNSPECV_ATOMIC_EXCHG))
    (clobber (reg:CC CC_REGNUM))
    (clobber (match_scratch:SI 4 "=&r"))]
-  ""
+  "!TARGET_LSE"
   "#"
   "&& epilogue_completed"
   [(const_int 0)]