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util/bufferiszero: Remove useless prefetches 

Use of prefetching in bufferiszero.c is quite questionable:

- prefetches are issued just a few CPU cycles before the corresponding
  line would be hit by demand loads;

- they are done for simple access patterns, i.e. where hardware
  prefetchers can perform better;

- they compete for load ports in loops that should be limited by load
  port throughput rather than ALU throughput.

Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
Signed-off-by: Mikhail Romanov <mmromanov@ispras.ru>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240206204809.9859-5-amonakov@ispras.ru>
This commit is contained in:
Alexander Monakov 2024-02-06 23:48:07 +03:00 committed by Richard Henderson
parent cbe3d52646
commit 93a6085618
1 changed files with 0 additions and 3 deletions
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3
util/bufferiszero.c
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@ -50,7 +50,6 @@ static bool buffer_is_zero_integer(const void *buf, size_t len)
const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8);
for (; p + 8 <= e; p += 8) {
__builtin_prefetch(p + 8);
if (t) {
return false;
}
@ -80,7 +79,6 @@ buffer_zero_sse2(const void *buf, size_t len)
/* Loop over 16-byte aligned blocks of 64. */
while (likely(p <= e)) {
__builtin_prefetch(p);
t = _mm_cmpeq_epi8(t, zero);
if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) {
return false;
@ -111,7 +109,6 @@ buffer_zero_avx2(const void *buf, size_t len)
/* Loop over 32-byte aligned blocks of 128. */
while (p <= e) {
__builtin_prefetch(p);
if (unlikely(!_mm256_testz_si256(t, t))) {
return false;
}