https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117297
--- Comment #4 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:387dba05e4207fc3f9a2f2bcb09a343a999c76fc commit r15-5443-g387dba05e4207fc3f9a2f2bcb09a343a999c76fc Author: Richard Sandiford <richard.sandif...@arm.com> Date: Tue Nov 19 10:19:24 2024 +0000 Avoid repeated calls to temporarily_undo_changes [PR117297] In an attempt to reduce compile time, rtl-ssa computes the cost of existing instructions lazily rather than eagerly. However, this means that it might need to calculate the cost of an existing instruction while a change group is already in progress for the instruction. rtl_ssa::insn_info::calculate_cost therefore temporarily undoes any in-progress changes in order to get back the original pattern and insn code. rtl-ssa's main use of insn costs is in rtl_ssa::changes_are_worthwhile, which calculates the cost of a change involving an arbitrary number of instructions. Summing up the original cost of N instructions while those N instructions have in-progress changes could lead to O(N*N) rtl changes, since each lazy calculation might have to temporarily undo the changes to all N instructions. We can avoid that by converting the current temporarily_undo_changes/ redo_changes pair into an RAII class and extending it to allow nested uses. rtl_ssa::changes_are_worthwhile can then undo the in-progress changes once, before computing the original cost of all the instructions. gcc/ PR rtl-optimization/117297 * recog.h (temporarily_undo_changes, redo_changes): Delete in favor of... (undo_recog_changes): ...this new RAII class. * fwprop.cc (should_replace_address): Update accordingly. (fwprop_propagation::check_mem): Likewise. (try_fwprop_subst_note): Likewise. (try_fwprop_subst_pattern): Likewise. * rtl-ssa/insns.cc (insn_info::calculate_cost): Likewise. * rtl-ssa/changes.cc (rtl_ssa::changes_are_worthwhile): Temporarily undo all in-progress changes while computing the cost of the original sequence. * recog.cc (temporarily_undone_changes): Replace with... (undo_recog_changes::s_num_changes): ...this static member variable. (validate_change_1): Update check accordingly. (confirm_change_group): Likewise. (num_validated_changes): Likewise. (temporarily_undo_changes): Replace with... (undo_recog_changes::undo_recog_changes): ...this constructor. (redo_changes): Replace with... (undo_recog_changes::~undo_recog_changes): ...this destructor.
