diff options
Diffstat (limited to 'gcc/tree-ssa-loop-prefetch.c')
| -rw-r--r-- | gcc/tree-ssa-loop-prefetch.c | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/gcc/tree-ssa-loop-prefetch.c b/gcc/tree-ssa-loop-prefetch.c index f828ed3..4889604 100644 --- a/gcc/tree-ssa-loop-prefetch.c +++ b/gcc/tree-ssa-loop-prefetch.c @@ -225,6 +225,17 @@ struct mem_ref_group #define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) +/* Do not generate a prefetch if the unroll factor is significantly less + than what is required by the prefetch. This is to avoid redundant + prefetches. For example, if prefetch_mod is 16 and unroll_factor is + 1, this means prefetching requires unrolling the loop 16 times, but + the loop is not going to be unrolled. In this case (ratio = 16), + prefetching is not likely to be beneficial. */ + +#ifndef PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO +#define PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO 8 +#endif + /* The memory reference. */ struct mem_ref @@ -921,6 +932,12 @@ schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, if (!should_issue_prefetch_p (ref)) continue; + /* The loop is far from being sufficiently unrolled for this + prefetch. Do not generate prefetch to avoid many redudant + prefetches. */ + if (ref->prefetch_mod / unroll_factor > PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO) + continue; + /* If we need to prefetch the reference each PREFETCH_MOD iterations, and we unroll the loop UNROLL_FACTOR times, we need to insert ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each |