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x86: improve bitop code generation with clang

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This uses the new ASM_INPUT_RM macro to avoid the bad code generation
issue that clang has with more generic asm inputs.

This ends up avoiding generating code like this:

 	mov    %r10,(%rsp)
 	tzcnt  (%rsp),%rcx

which now becomes just

 	tzcnt  %r10,%rcx

and in the process ends up also removing a few unnecessary stack frames
when the only use was that pointless "asm uses memory location off stack".

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2024-04-09 11:55:07 -07:00
parent 7453b94851
commit b9b60b3199
1 changed files with 5 additions and 5 deletions
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10
arch/x86/include/asm/bitops.h
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@ -250,7 +250,7 @@ static __always_inline unsigned long variable__ffs(unsigned long word)
{
asm("rep; bsf %1,%0"
: "=r" (word)
: "rm" (word));
: ASM_INPUT_RM (word));
return word;
}
@ -297,7 +297,7 @@ static __always_inline unsigned long __fls(unsigned long word)
asm("bsr %1,%0"
: "=r" (word)
: "rm" (word));
: ASM_INPUT_RM (word));
return word;
}
@ -320,7 +320,7 @@ static __always_inline int variable_ffs(int x)
*/
asm("bsfl %1,%0"
: "=r" (r)
: "rm" (x), "0" (-1));
: ASM_INPUT_RM (x), "0" (-1));
#elif defined(CONFIG_X86_CMOV)
asm("bsfl %1,%0\n\t"
"cmovzl %2,%0"
@ -377,7 +377,7 @@ static __always_inline int fls(unsigned int x)
*/
asm("bsrl %1,%0"
: "=r" (r)
: "rm" (x), "0" (-1));
: ASM_INPUT_RM (x), "0" (-1));
#elif defined(CONFIG_X86_CMOV)
asm("bsrl %1,%0\n\t"
"cmovzl %2,%0"
@ -416,7 +416,7 @@ static __always_inline int fls64(__u64 x)
*/
asm("bsrq %1,%q0"
: "+r" (bitpos)
: "rm" (x));
: ASM_INPUT_RM (x));
return bitpos + 1;
}
#else