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>

diff --git a/arch/mips/include/asm/bitops.h b/arch/mips/include/asm/bitops.h
index 9f935f6aa996ddfd573b9ccb4f6261118934a415..0cf29bd5dc5c538e807d6b1e4021a1b111d869ec 100644 (file)
--- a/arch/mips/include/asm/bitops.h
+++ b/arch/mips/include/asm/bitops.h
@@ -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"