[Bug tree-optimization/114277] [12/13/14/15 Regression] Missed optimization: x*(x||b) => x

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114277

--- Comment #13 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jeff Law <law@gcc.gnu.org>:

https://gcc.gnu.org/g:2c0a9b7fb7902522fb8484342fcc19fd44df53e6

commit r15-7313-g2c0a9b7fb7902522fb8484342fcc19fd44df53e6
Author: Jeff Law <jlaw@ventanamicro.com>
Date:   Fri Jan 31 16:59:35 2025 -0700

    [committed][PR tree-optimization/114277] Fix missed optimization for
multiplication against boolean value

    Andrew, Raphael and I have all poked at it in various ways over the last
year
    or so.  I think when Raphael and I first looked at it I sent us down a bit
of
    rathole.

    In particular it's odd that we're using a multiply to implement a select
and it
    seemed like recognizing the idiom and rewriting into a conditional move was
the
    right path.  That looked reasonably good for the test, but runs into
problems
    with min/max detection elsewhere.

    I think that initial investigation somewhat polluted our thinking.  The
    regression can be fixed with a fairly simple match.pd pattern.

    Essentially we want to handle

    x * (x || b) -> x
    x * !(x || b) -> 0

    There's simplifications that can be made for "&&" cases, but I haven't seen
    them in practice.  Rather than drop in untested patterns, I'm leaving that
as a
    future todo.

    My original was two match.pd patterns.  Andrew combined them into a single
    pattern.  I've made this conditional on GIMPLE as an earlier version that
    simplified to a conditional move showed that when applied on GENERIC we
could
    drop an operand with a side effect which is clearly not good.

    I've bootstrapped and regression tested this on x86.  I've also tested on
the
    various embedded targets in my tester.

            PR tree-optimization/114277
    gcc/
            * match.pd (a * (a || b) -> a): New pattern.
            (a * !(a || b) -> 0): Likewise.

    gcc/testsuite
            * gcc.target/i386/pr114277.c: New test.
            * gcc.target/riscv/pr114277.c: Likewise.

            Co-author:  Andrew Pinski <quic_apinski@quicinc.com>