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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/110587] [14 regression] 96% pr28071.c compile
 time regression since r14-2337-g37a231cc7594d1
Date: Fri, 28 Jul 2023 08:40:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110587

--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:

https://gcc.gnu.org/g:095eb138f736d94dabf9a07a6671bd351be0e66a

commit r14-2851-g095eb138f736d94dabf9a07a6671bd351be0e66a
Author: Roger Sayle <roger@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 underl=
ying
    cause.  As noted previously, the pathological test case pr28071.c conta=
ins
    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 simpli=
fy
    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 th=
at
    redundancy.

    The -fdump-tree-expand for pr28071.c compiled with -O0 currently contai=
ns
    777K lines, with this patch it contains 717K lines, i.e. saving about 6=
0K
    lines (admittedly of debugging text output, but it makes the point).

    2023-07-28  Roger Sayle  <roger@nextmovesoftware.com>
                Richard Biener  <rguenther@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.=