> On Jan 30, 2017, at 5:50 PM, Maxim Kuvyrkov <maxim.kuvyr...@linaro.org> wrote: > >> On Jan 30, 2017, at 3:23 PM, Kyrill Tkachov <kyrylo.tkac...@foss.arm.com> >> wrote: >> >> Hi Maxim, >> >> On 30/01/17 12:06, Maxim Kuvyrkov wrote: >>> This patch enables prefetching at -O3 for aarch64 cores that set >>> "simultaneous prefetches" parameter above 0. There are currently no such >>> settings, so this patch doesn't change default code generation. >>> >>> I'm now working on improvements to -fprefetch-loop-arrays pass to make it >>> suitable for -O2. I'll post this work in the next month. >>> >>> Bootstrapped and regtested on x86_64-linux-gnu and aarch64-linux-gnu. >>> >> >> Are you aiming to get this in for GCC 8? >> I have one small comment on this patch: >> >> + /* Enable sw prefetching at -O3 for CPUS that have prefetch, and we >> + have deemed it beneficial (signified by setting >> + prefetch.num_slots to 1 or more). */ >> + if (flag_prefetch_loop_arrays < 0 >> + && HAVE_prefetch >> >> HAVE_prefetch will always be true on aarch64. >> I imagine midend code that had logic like this would need this check, but >> aarch64-specific code shouldn't need it. > > Agree, I'll remove HAVE_prefetch. > > This pattern was copied from other backends, and HAVE_prefetch is most likely > a historical artifact.
Andrew raised a good point in the review of his patch that it is a bad idea to use one of prefetching parameters (simultaneous_prefetches) as indicator for whether to enable prefetching pass by default. Indeed there are cases when we want to set simultaneous_prefetch according to HW documentation (or experimental results), but not enable prefetching pass by default. This update to the patch addresses it. The patch adds a new explicit field to prefetch tuning structure "default_opt_level" that sets optimization level from which prefetching should be enabled by default. The current value is to enable prefetching at -O3; additionally, this parameter will come handy for enabling prefetching at -O2 [when it is ready]. -- Maxim Kuvyrkov www.linaro.org
0005-Enable-fprefetch-loop-arrays-at-O3-for-cores-that-be.patch
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