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Subject: [Bug tree-optimization/96392] Optimize x+0.0 if x is an integer
Date: Fri, 11 Jun 2021 16:18:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96392

--- Comment #1 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:5b02ed4b87685c0f7c5da9b46cde3ce56fcfd457

commit r12-1393-g5b02ed4b87685c0f7c5da9b46cde3ce56fcfd457
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Fri Jun 11 17:15:38 2021 +0100

    [PATCH] PR tree-optimization/96392 Optimize x+0.0 if x is an integer

    The patch implements a missed optimization enhancement.  Under usual
    IEEE rules, x+0.0 can't be simplified to x when x might potentially
    be an IEEE minus zero (-0.0).  The current logic in the middle-end
    checks whether the type of x should honor signed zeros, but with this
    patch we introduce tree_expr_maybe_real_minus_zero_p that allows us
    to confirm that the value can't possibly be -0.0, for example, the resu=
lt
    of a conversion from an integer type, or the result of fabs (or has a
    type that doesn't honor signed zero).

    Whilst modifying match.pd, I also converted some additional folding
    transformations from "testing the type" to "testing the value".

    2020-06-10  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            PR tree-optimization/96392
            * fold-const.c (fold_real_zero_addition_p): Take both arguments
            of the addition or subtraction, not just the zero.  Use this
            other argument in tests for signaling NaNs and signed zeros.
            (tree_expr_maybe_real_minus_zero_p): New predicate.
            * fold-const.h (fold_real_zero_addition_p): Update prototype.
            (tree_expr_maybe_real_minus_zero_p): New function prototype.
            * match.pd: Update calls to fold_real_zero_addition_p.
            Replace HONOR_NANS with tree_expr_maybe_nan_p.
            Replace HONOR_SIGNED_ZEROS with tree_expr_maybe_real_minus_zero=
_p.
            Replace HONOR_SNANS with tree_expr_maybe_signaling_nan_p.
            * tree-ssa-reassoc.c (eliminate_using_constants): Update
            call to fold_real_zero_addition_p.

    gcc/testsuite/ChangeLog
            PR tree-optimization/96392
            * gcc.dg/pr96392.c: New test.=