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Re: [PATCH] Fix up strtod_l.c for -O0
On Tue, Feb 19, 2013 at 09:50:20AM -0500, Carlos O'Donell wrote:
> * I have a slight preference for making the entire function into a macro.
> However, I have no evidence that this would generate higher performing
> code in this case.
Here it is as a macro without inline helpers.
If I remove the
Implemented as a macro, so that __builtin_constant_p works even at -O0.
and following empty line in comment, so that line numbers match, then in
the whole libc.so the difference is on x86_64 just:
- 3fa9d: 40 3a 33 cmp (%rbx),%sil
+ 3fa9d: 40 38 33 cmp %sil,(%rbx)
in a single spot. Of course with the added two lines there are various
differences, because __assert_fail arguments differ (wasn't doing non-debug
build).
2013-02-19 Jakub Jelinek <jakub@redhat.com>
* stdlib/strtod_l.c (__mpn_lshift_1): Rewritten as function-like
macro.
diff --git a/stdlib/strtod_l.c b/stdlib/strtod_l.c
index 5959354..47247b5 100644
--- a/stdlib/strtod_l.c
+++ b/stdlib/strtod_l.c
@@ -444,28 +444,30 @@ str_to_mpn (const STRING_TYPE *str, int digcnt, mp_limb_t *n, mp_size_t *nsize,
/* Shift {PTR, SIZE} COUNT bits to the left, and fill the vacated bits
with the COUNT most significant bits of LIMB.
- Tege doesn't like this function so I have to write it here myself. :)
+ Implemented as a macro, so that __builtin_constant_p works even at -O0.
+
+ Tege doesn't like this macro so I have to write it here myself. :)
--drepper */
-static inline void
-__attribute ((always_inline))
-__mpn_lshift_1 (mp_limb_t *ptr, mp_size_t size, unsigned int count,
- mp_limb_t limb)
-{
- if (__builtin_constant_p (count) && count == BITS_PER_MP_LIMB)
- {
- /* Optimize the case of shifting by exactly a word:
- just copy words, with no actual bit-shifting. */
- mp_size_t i;
- for (i = size - 1; i > 0; --i)
- ptr[i] = ptr[i - 1];
- ptr[0] = limb;
- }
- else
- {
- (void) __mpn_lshift (ptr, ptr, size, count);
- ptr[0] |= limb >> (BITS_PER_MP_LIMB - count);
- }
-}
+#define __mpn_lshift_1(ptr, size, count, limb) \
+ do \
+ { \
+ mp_limb_t *__ptr = (ptr); \
+ if (__builtin_constant_p (count) && count == BITS_PER_MP_LIMB) \
+ { \
+ mp_size_t i; \
+ for (i = (size) - 1; i > 0; --i) \
+ __ptr[i] = __ptr[i - 1]; \
+ __ptr[0] = (limb); \
+ } \
+ else \
+ { \
+ /* We assume count > 0 && count < BITS_PER_MP_LIMB here. */ \
+ unsigned int __count = (count); \
+ (void) __mpn_lshift (__ptr, __ptr, size, __count); \
+ __ptr[0] |= (limb) >> (BITS_PER_MP_LIMB - __count); \
+ } \
+ } \
+ while (0)
#define INTERNAL(x) INTERNAL1(x)
Jakub