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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/113231] x86_64 uses SSE instructions for `*mem <<=
 const` at -Os
Date: Sun, 07 Jan 2024 17:43:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113231

--- Comment #5 from GCC 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:0a8aba760f62e9d66cc5610ecc276c1f0befc651

commit r14-6985-g0a8aba760f62e9d66cc5610ecc276c1f0befc651
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Sun Jan 7 17:42:00 2024 +0000

    i386: PR target/113231: Improved costs in Scalar-To-Vector (STV) pass.

    This patch improves the cost/gain calculation used during the i386
backend's
    SImode/DImode scalar-to-vector (STV) conversion pass.  The current code
    handles loads and stores, but doesn't consider that converting other
    scalar operations with a memory destination, requires an explicit load
    before and an explicit store after the vector equivalent.

    To ease the review, the significant change looks like:

             /* For operations on memory operands, include the overhead
                of explicit load and store instructions.  */
             if (MEM_P (dst))
               igain +=3D !optimize_insn_for_size_p ()
                        ? -COSTS_N_BYTES (8);
                        : (m * (ix86_cost->int_load[2]
                                + ix86_cost->int_store[2])
                           - (ix86_cost->sse_load[sse_cost_idx] +
                              ix86_cost->sse_store[sse_cost_idx]));

    however the patch itself is complicated by a change in indentation
    which leads to a number of lines with only whitespace changes.
    For architectures where integer load/store costs are the same as
    vector load/store costs, there should be no change without -Os/-Oz.

    2024-01-07  Roger Sayle  <roger@nextmovesoftware.com>
                Uros Bizjak  <ubizjak@gmail.com>

    gcc/ChangeLog
            PR target/113231
            * config/i386/i386-features.cc (compute_convert_gain): Include
            the overhead of explicit load and store (movd) instructions when
            converting non-store scalar operations with memory destinations.
            Various indentation whitespace fixes.

    gcc/testsuite/ChangeLog
            PR target/113231
            * gcc.target/i386/pr113231.c: New test case.=