x86: improve bitop code generation with clang

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>

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 990eb686ca67bd9fe4fdcff11c159d50f5adb32e..b96d45944c5908a153bf5a8894d7b4c0b68fa290 100644 (file)
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -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