[Bug tree-optimization/116024] [14/15 Regression] unnecessary integer comparison(s) for a simple loop since r14-5628-g53ba8d669550d3

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116024

--- Comment #11 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jeff Law <l...@gcc.gnu.org>:

https://gcc.gnu.org/g:e5f5cffb8c8243896a9d3bd0e2b8f14c70f8df1e

commit r15-4188-ge5f5cffb8c8243896a9d3bd0e2b8f14c70f8df1e
Author: Artemiy Volkov <artemiy.vol...@synopsys.com>
Date:   Tue Oct 8 18:04:13 2024 -0600

    tree-optimization/116024 - simplify C1-X cmp C2 for wrapping signed types

    Implement a match.pd transformation inverting the sign of X in
    C1 - X cmp C2, where C1 and C2 are integer constants and X is
    of a wrapping signed type, by observing that:

    (a) If cmp is == or !=, simply move X and C2 to opposite sides of
    the comparison to arrive at X cmp C1 - C2.

    (b) If cmp is <:
            - C1 - X < C2 means that C1 - X spans the values of -INF,
              -INF + 1, ..., C2 - 1;
            - Therefore, X is one of C1 - -INF, C1 - (-INF + 1), ...,
              C1 - C2 + 1;
            - Subtracting (C1 + 1), X - (C1 + 1) is one of - (-INF) - 1,
              - (-INF) - 2, ..., -C2;
            - Using the fact that - (-INF) - 1 is +INF, derive that
              X - (C1 + 1) spans the values +INF, +INF - 1, ..., -C2;
            - Thus, the original expression can be simplified to
              X - (C1 + 1) > -C2 - 1.

    (c) Similarly, C1 - X <= C2 is equivalent to X - (C1 + 1) >= -C2 - 1.

    (d) The >= and > cases are negations of (b) and (c), respectively.

    (e) In all cases, the expression -C2 - 1 can be shortened to
    bit_not (C2).

    This transformation allows to occasionally save load-immediate /
    subtraction instructions, e.g. the following statement:

    10 - (int)f() >= 20;

    now compiles to

    addi    a0,a0,-11
    slti    a0,a0,-20

    instead of

    li      a5,10
    sub     a0,a5,a0
    slti    t0,a0,20
    xori    a0,t0,1

    on 32-bit RISC-V when compiled with -fwrapv.

    Additional examples can be found in the newly added test file.  This
    patch has been bootstrapped and regtested on aarch64, x86_64, and i386,
    and additionally regtested on riscv32.

    gcc/ChangeLog:

            PR tree-optimization/116024
            * match.pd: New transformation around integer comparison.

    gcc/testsuite/ChangeLog:

            * gcc.dg/tree-ssa/pr116024-1-fwrapv.c: New test.