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Subject[PATCH] compiler-gcc.h: Remove ancient workaround for gcc PR 58670
Date
The workaround for 'asm goto' miscompilation introduces a compiler
barrier quirk that inhibits many useful compiler optimizations. For
example, __try_cmpxchg_user compiles to:

11375: 41 8b 4d 00 mov 0x0(%r13),%ecx
11379: 41 8b 02 mov (%r10),%eax
1137c: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
11380: 0f 94 c2 sete %dl
11383: 84 d2 test %dl,%dl
11385: 75 c4 jne 1134b <...>
11387: 41 89 02 mov %eax,(%r10)

where the barrier inhibits flags propagation from asm when
compiled with gcc-12.

When the mentioned quirk is removed, the following code is generated:

11553: 41 8b 4d 00 mov 0x0(%r13),%ecx
11557: 41 8b 02 mov (%r10),%eax
1155a: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
1155e: 74 c9 je 11529 <...>
11560: 41 89 02 mov %eax,(%r10)

The refered compiler bug:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670

was fixed for gcc-4.8.2.

Current minimum required version of GCC is version 5.1 which has
the above 'asm goto' miscompilation fixed, so remove the workaround.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/compiler-gcc.h | 11 -----------
1 file changed, 11 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index a0c55eeaeaf1..9b157b71036f 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -66,17 +66,6 @@
__builtin_unreachable(); \
} while (0)

-/*
- * GCC 'asm goto' miscompiles certain code sequences:
- *
- * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
- *
- * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
- *
- * (asm goto is automatically volatile - the naming reflects this.)
- */
-#define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
-
#if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP)
#define __HAVE_BUILTIN_BSWAP32__
#define __HAVE_BUILTIN_BSWAP64__
--
2.35.3
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