https://gcc.gnu.org/bugzilla/show_bug.cgi?id=28071
--- Comment #71 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:095eb138f736d94dabf9a07a6671bd351be0e66a commit r14-2851-g095eb138f736d94dabf9a07a6671bd351be0e66a Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Fri Jul 28 09:39:46 2023 +0100 PR rtl-optimization/110587: Reduce useless moves in compile-time hog. This patch is one of a series of fixes for PR rtl-optimization/110587, a compile-time regression with -O0, that attempts to address the underlying cause. As noted previously, the pathological test case pr28071.c contains a large number of useless register-to-register moves that can produce quadratic behaviour (in LRA). These moves are generated during RTL expansion in emit_group_load_1, where the middle-end attempts to simplify the source before calling extract_bit_field. This is reasonable if the source is a complex expression (from before the tree-ssa optimizers), or a SUBREG, or a hard register, but it's not particularly useful to copy a pseudo register into a new pseudo register. This patch eliminates that redundancy. The -fdump-tree-expand for pr28071.c compiled with -O0 currently contains 777K lines, with this patch it contains 717K lines, i.e. saving about 60K lines (admittedly of debugging text output, but it makes the point). 2023-07-28 Roger Sayle <ro...@nextmovesoftware.com> Richard Biener <rguent...@suse.de> gcc/ChangeLog PR middle-end/28071 PR rtl-optimization/110587 * expr.cc (emit_group_load_1): Simplify logic for calling force_reg on ORIG_SRC, to avoid making a copy if the source is already in a pseudo register.
