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Commit cb5d4aad authored by Maciej W. Rozycki's avatar Maciej W. Rozycki Committed by Ralf Baechle
Browse files

MIPS: bitops.h: Avoid inline asm for constant FLS 



GCC is smart enough to substitute the final result for FLS calculations
as implemented in the fallback C code we have in `__fls' and `fls'
applied to constant values.  The presence of inline asm defeats the
compiler though, forcing it to emit extraneous CLZ/DCLZ calculation for
processors that support these instructions.

Use `__builtin_constant_p' then to avoid inline asm altogether for
constants.

Signed-off-by: default avatarMaciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9681/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 2cfcf8a8

arch/mips/include/asm/bitops.h

+4 −3
Original line number Diff line number Diff line
@@ -481,7 +481,7 @@ static inline unsigned long __fls(unsigned long word) 
{

	int num;



	if (BITS_PER_LONG == 32 &&

	if (BITS_PER_LONG == 32 && !__builtin_constant_p(word) &&

	    __builtin_constant_p(cpu_has_clo_clz) && cpu_has_clo_clz) {

		__asm__(

		"	.set	push					\n"
@@ -494,7 +494,7 @@ static inline unsigned long __fls(unsigned long word) 
		return 31 - num;

	}



	if (BITS_PER_LONG == 64 &&

	if (BITS_PER_LONG == 64 && !__builtin_constant_p(word) &&

	    __builtin_constant_p(cpu_has_mips64) && cpu_has_mips64) {

		__asm__(

		"	.set	push					\n"
@@ -559,7 +559,8 @@ static inline int fls(int x) 
{

	int r;



	if (__builtin_constant_p(cpu_has_clo_clz) && cpu_has_clo_clz) {

	if (!__builtin_constant_p(x) &&

	    __builtin_constant_p(cpu_has_clo_clz) && cpu_has_clo_clz) {

		__asm__(

		"	.set	push					\n"

		"	.set	"MIPS_ISA_LEVEL"			\n"