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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: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9681/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
hifive-unleashed-5.1
Maciej W. Rozycki 2015-04-03 23:25:00 +01:00 committed by Ralf Baechle
parent 2cfcf8a831
commit cb5d4aad68
1 changed files with 4 additions and 3 deletions
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7
arch/mips/include/asm/bitops.h
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@ -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"