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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>
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@ -50,7 +50,6 @@ static bool buffer_is_zero_integer(const void *buf, size_t len)
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const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8);
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for (; p + 8 <= e; p += 8) {
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__builtin_prefetch(p + 8);
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if (t) {
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return false;
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}
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@ -80,7 +79,6 @@ buffer_zero_sse2(const void *buf, size_t len)
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/* Loop over 16-byte aligned blocks of 64. */
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while (likely(p <= e)) {
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__builtin_prefetch(p);
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t = _mm_cmpeq_epi8(t, zero);
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if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) {
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return false;
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@ -111,7 +109,6 @@ buffer_zero_avx2(const void *buf, size_t len)
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/* Loop over 32-byte aligned blocks of 128. */
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while (p <= e) {
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__builtin_prefetch(p);
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if (unlikely(!_mm256_testz_si256(t, t))) {
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return false;
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}
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