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>
diff --git a/util/bufferiszero.c b/util/bufferiszero.c
index 972f394..00118d6 100644
--- a/util/bufferiszero.c
+++ b/util/bufferiszero.c
@@ -50,7 +50,6 @@
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 @@
/* 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 @@
/* Loop over 32-byte aligned blocks of 128. */
while (p <= e) {
- __builtin_prefetch(p);
if (unlikely(!_mm256_testz_si256(t, t))) {
return false;
}
