https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113613
--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:ff442719cdb64c9df9d069af88e90d51bee6fb56 commit r14-9157-gff442719cdb64c9df9d069af88e90d51bee6fb56 Author: Richard Sandiford <richard.sandif...@arm.com> Date: Fri Feb 23 14:12:55 2024 +0000 aarch64: Spread out FPR usage between RA regions [PR113613] early-ra already had code to do regrename-style "broadening" of the allocation, to promote scheduling freedom. However, the pass divides the function into allocation regions and this broadening only worked within a single region. This meant that if a basic block contained one subblock of FPR use, followed by a point at which no FPRs were live, followed by another subblock of FPR use, the two subblocks would tend to reuse the same registers. This in turn meant that it wasn't possible to form LDP/STP pairs between them. The failure to form LDPs and STPs in the testcase was a regression from GCC 13. The patch adds a simple heuristic to prefer less recently used registers in the event of a tie. gcc/ PR target/113613 * config/aarch64/aarch64-early-ra.cc (early_ra::m_current_region): New member variable. (early_ra::m_fpr_recency): Likewise. (early_ra::start_new_region): Bump m_current_region. (early_ra::allocate_colors): Prefer less recently used registers in the event of a tie. Add a comment to explain why we prefer(ed) higher-numbered registers. (early_ra::find_oldest_color): Prefer less recently used registers here too. (early_ra::finalize_allocation): Update recency information for allocated registers. (early_ra::process_blocks): Initialize m_current_region and m_fpr_recency. gcc/testsuite/ PR target/113613 * gcc.target/aarch64/pr113613.c: New test.
