diff options
| author | Heiko Carstens <hca@linux.ibm.com> | 2025-09-16 15:48:02 +0200 |
|---|---|---|
| committer | Alexander Gordeev <agordeev@linux.ibm.com> | 2025-09-18 14:06:40 +0200 |
| commit | 79161603952c842eb22313f2060051b359b0a592 (patch) | |
| tree | 0fa4197ad426e1eac6b44b3acf6103c5278e85d1 | |
| parent | f72e2cff13aefe305fc8fc6afe4f43626e4ad88c (diff) | |
s390/bitops: Use __assume() for __flogr() inline assembly return value
Use __assume() to tell compilers that the output operand of the __flogr()
inline assembly contains a value in the range of 0..64. This allows to
optimize the logical AND operation away.
This reduces the kernel image size by 2804 bytes (defconfig, gcc 15.2.0).
Suggested-by: Juergen Christ <jchrist@linux.ibm.com>
Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
| -rw-r--r-- | arch/s390/include/asm/bitops.h | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/arch/s390/include/asm/bitops.h b/arch/s390/include/asm/bitops.h index 9bc70acbac9e..ac94672db817 100644 --- a/arch/s390/include/asm/bitops.h +++ b/arch/s390/include/asm/bitops.h @@ -132,9 +132,10 @@ static inline bool test_bit_inv(unsigned long nr, */ static __always_inline unsigned char __flogr(unsigned long word) { - if (__builtin_constant_p(word)) { - unsigned long bit = 0; + unsigned long bit; + if (__builtin_constant_p(word)) { + bit = 0; if (!word) return 64; if (!(word & 0xffffffff00000000UL)) { @@ -169,7 +170,14 @@ static __always_inline unsigned char __flogr(unsigned long word) asm volatile( " flogr %[rp],%[rp]\n" : [rp] "+d" (rp.pair) : : "cc"); - return rp.even & 127; + bit = rp.even; + /* + * The result of the flogr instruction is a value in the range + * of 0..64. Let the compiler know that the AND operation can + * be optimized away. + */ + __assume(bit <= 64); + return bit & 127; } } |