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multiload: use parallel accumulators in stream-sum #61

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multiload: use parallel accumulators in stream-sum #61

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7 changes: 7 additions & 0 deletions multiload.c
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Original file line number Diff line number Diff line change
Expand Up @@ -690,6 +690,13 @@ static void load_stream_sum(per_thread_t *t) {
uint64_t active_ns = t->x.load_active_ns;
do {
CHECK_DUTY_CYCLE(interval_ns, active_ns)
// -fno-unroll-loops (Makefile CFLAGS) also disables clang vectorizer
// interleaving, leaving one accumulator and a loop-carried add chain.
// Request independent accumulators so the loop is load-bound. Guarded
// because GCC warns on unknown pragmas, and the Makefile uses -Werror.
#if defined(__clang__)
#pragma clang loop interleave_count(4)
#endif
for (i = 0; i < N; ++i) {
s += a[i];
}
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