Introduce prefetch-dynamic-strides option

Programming / Compilers / GCC - luisgpm [138bc75d-0d04-0410-961f-82ee72b054a4] - 7 May 2018 14:12 EDT

The following patch adds an option to control software prefetching of memory references with non-constant/unknown strides.

Currently we prefetch these references if the pass thinks there is benefit to doing so. But, since this is all based on heuristics, it's not always the case that we end up with better performance.

For Falkor there is also the problem of conflicts with the hardware prefetcher, so we need to be more conservative in terms of what we issue software prefetch hints for.

This also aligns GCC with what LLVM does for Falkor.

Similarly to the previous patch, the defaults guarantee no change in behavior for other targets and architectures.

2018-05-07 Luis Machado

gcc/
- config/aarch64/aarch64-protos.h (cpu_prefetch_tune) : New const bool field.
- config/aarch64/aarch64.c (generic_prefetch_tune): Update to include prefetch_dynamic_strides. (exynosm1_prefetch_tune): Likewise. (thunderxt88_prefetch_tune): Likewise. (thunderx_prefetch_tune): Likewise. (thunderx2t99_prefetch_tune): Likewise. (qdf24xx_prefetch_tune): Likewise. Set prefetch_dynamic_strides to false. (aarch64_override_options_internal): Update to set PARAM_PREFETCH_DYNAMIC_STRIDES.
- doc/invoke.texi (prefetch-dynamic-strides): Document new option.
- params.def (PARAM_PREFETCH_DYNAMIC_STRIDES): New.
- params.h (PARAM_PREFETCH_DYNAMIC_STRIDES): Define.
- tree-ssa-loop-prefetch.c (should_issue_prefetch_p): Account for prefetch-dynamic-strides setting.

38bd90a9a88 Introduce prefetch-dynamic-strides option.
gcc/ChangeLog | 20 ++++++++++++++++++++
gcc/config/aarch64/aarch64-protos.h | 3 +++
gcc/config/aarch64/aarch64.c | 11 +++++++++++
gcc/doc/invoke.texi | 10 ++++++++++
gcc/params.def | 9 +++++++++
gcc/params.h | 2 ++
gcc/tree-ssa-loop-prefetch.c | 10 ++++++++++
7 files changed, 65 insertions(+)

Upstream: gcc.gnu.org


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