Ping^5 for patches 2-4: https://gcc.gnu.org/pipermail/gcc-patches/2025-January/672677.html https://gcc.gnu.org/pipermail/gcc-patches/2025-January/672678.html https://gcc.gnu.org/pipermail/gcc-patches/2025-January/672679.html
On 12/02/2025 11:20, Alex Coplan wrote: > Ping > > On 03/02/2025 14:46, Tamar Christina wrote: > > Ping > > > > > -----Original Message----- > > > From: Tamar Christina > > > Sent: Friday, January 24, 2025 9:18 AM > > > To: Alex Coplan <alex.cop...@arm.com>; gcc-patches@gcc.gnu.org > > > Cc: Richard Biener <rguent...@suse.de>; Jan Hubicka <hubi...@ucw.cz> > > > Subject: RE: [PATCH 2/4] cfgloopmanip: Add infrastructure for scaling of > > > multi-exit > > > loops [PR117790] > > > > > > ping > > > > > > > -----Original Message----- > > > > From: Tamar Christina > > > > Sent: Wednesday, January 15, 2025 2:08 PM > > > > To: Alex Coplan <alex.cop...@arm.com>; gcc-patches@gcc.gnu.org > > > > Cc: Richard Biener <rguent...@suse.de>; Jan Hubicka <hubi...@ucw.cz> > > > > Subject: RE: [PATCH 2/4] cfgloopmanip: Add infrastructure for scaling > > > > of multi- > > > exit > > > > loops [PR117790] > > > > > > > > Ping > > > > > > > > > -----Original Message----- > > > > > From: Alex Coplan <alex.cop...@arm.com> > > > > > Sent: Monday, January 6, 2025 11:35 AM > > > > > To: gcc-patches@gcc.gnu.org > > > > > Cc: Richard Biener <rguent...@suse.de>; Jan Hubicka <hubi...@ucw.cz>; > > > Tamar > > > > > Christina <tamar.christ...@arm.com> > > > > > Subject: [PATCH 2/4] cfgloopmanip: Add infrastructure for scaling of > > > > > multi-exit > > > > > loops [PR117790] > > > > > > > > > > As it stands, scale_loop_profile doesn't correctly handle loops with > > > > > multiple exits. In particular, in the case where the expected niters > > > > > exceeds iteration_bound, scale_loop_profile attempts to reduce the > > > > > number of iterations with a call to scale_loop_frequencies, which > > > > > multiplies the count of each BB by a given probability. This > > > > > transformation preserves the relationships between the counts of the > > > > > BBs > > > > > within the loop (and thus the edge probabilities stay the same) but > > > > > this > > > > > cannot possibly work for loops with multiple exits, since in order for > > > > > the expected niters to reduce (and counts along exit edges to remain > > > > > the > > > > > same), the exit edge probabilities must increase, thus decreasing the > > > > > probabilities of the internal edges, meaning that the ratios of the > > > > > counts of the BBs inside the loop must change. So we need a different > > > > > approach (not a straightforward multiplicative scaling) to adjust the > > > > > expected niters of a loop with multiple exits. > > > > > > > > > > This patch introduces a new helper, flow_scale_loop_freqs, which can > > > > > be > > > > > used to correctly scale the profile of a loop with multiple exits. It > > > > > is parameterized by a probability (with which to scale the header and > > > > > therefore the expected niters) and a lambda which gives the desired > > > > > counts for the exit edges. In this patch, to make things simpler, > > > > > flow_scale_loop_freqs only handles loop shapes without internal > > > > > control > > > > > flow, and we introduce a predicate can_flow_scale_loop_freqs_p to test > > > > > whether a given loop meets these criteria. This restriction is > > > > > reasonable since this patch is motivated by fixing the profile > > > > > consistency for early break vectorization, and we don't currently > > > > > vectorize loops with internal control flow. We also fall back to a > > > > > multiplicative scaling (the status quo) for loops that > > > > > flow_scale_loop_freqs can't handle, so the patch should be a net > > > > > improvement. > > > > > > > > > > We wrap the call to flow_scale_loop_freqs in a helper > > > > > scale_loop_freqs_with_exit_counts which handles the above-mentioned > > > > > fallback. This wrapper is still generic in that it accepts a lambda > > > > > to > > > > > allow overriding the desired exit edge counts. We specialize this > > > > > with > > > > > another wrapper, scale_loop_freqs_hold_exit_counts (keeping the > > > > > counts along exit edges fixed), which is then used to implement the > > > > > niters-scaling case of scale_loop_profile, thus fixing this path > > > > > through > > > > > the function for loops with multiple exits. > > > > > > > > > > Finally, we expose two new wrapper functions in cfgloopmanip.h for use > > > > > in subsequent vectorizer patches. scale_loop_profile_hold_exit_counts > > > > > is a variant of scale_loop_profile which assumes we want to keep the > > > > > counts along exit edges of the loop fixed through both parts of the > > > > > transformation (including the initial probability scale). > > > > > scale_loop_freqs_with_new_exit_count is intended to be used in a > > > > > subsequent patch when adding a skip edge around the epilog, where the > > > > > reduction of count entering the loop is mirrored by a reduced count > > > > > along a given exit edge. > > > > > > > > > > Bootstrapped/regtested as a series on aarch64-linux-gnu, > > > > > x86_64-linux-gnu, and arm-linux-gnueabihf. OK for trunk? > > > > > > > > > > Thanks, > > > > > Alex > > > > > > > > > > gcc/ChangeLog: > > > > > > > > > > PR tree-optimization/117790 > > > > > * cfgloopmanip.cc (can_flow_scale_loop_freqs_p): New. > > > > > (flow_scale_loop_freqs): New. > > > > > (scale_loop_freqs_with_exit_counts): New. > > > > > (scale_loop_freqs_hold_exit_counts): New. > > > > > (scale_loop_profile): Refactor to use the newly-added > > > > > scale_loop_profile_1, and use scale_loop_freqs_hold_exit_counts > > > > > to > > > > > correctly handle reducing the expected niters for loops with > > > > > multiple > > > > > exits. > > > > > (scale_loop_freqs_with_new_exit_count): New. > > > > > (scale_loop_profile_1): New. > > > > > (scale_loop_profile_hold_exit_counts): New. > > > > > * cfgloopmanip.h (scale_loop_profile_hold_exit_counts): New. > > > > > (scale_loop_freqs_with_new_exit_count): New. > > > > > --- > > > > > gcc/cfgloopmanip.cc | 309 > > > > ++++++++++++++++++++++++++++++++++++++++-- > > > > > -- > > > > > gcc/cfgloopmanip.h | 7 + > > > > > 2 files changed, 294 insertions(+), 22 deletions(-) > >
