[Bug target/116275] [15 regression] ICE when building llvm-18.1.8 (convert_insn, at config/i386/i386-features.cc:1502)

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116275

--- Comment #6 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:7a970bd03f1d8eed7703db8a8db3c753ea68899f

commit r15-2880-g7a970bd03f1d8eed7703db8a8db3c753ea68899f
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Mon Aug 12 06:52:48 2024 +0100

    PR target/116275: Handle STV of *extenddi2_doubleword_highpart on i386.

    This patch resolves PR target/116275, a recent ICE-on-valid regression on
    -m32 caused by my recent change to enable STV of DImode arithmeric right
    shift on non-AVX512VL targets.  The oversight is that the i386 backend
    contains an *extenddi2_doubleword_highpart instruction (whose pattern
    is an arithmetic right shift of a left shift) that optimizes the case where
    sign-extension need only update the highpart word of a DImode value when
    generating 32-bit code (!TARGET_64BIT).  STV accepts this pattern as a
    candidate, as there are patterns to handle this form of extension on SSE
    using AVX512VL instructions (and previously ASHIFTRT was only allowed on
    AVX512VL).  Now that ASHIFTRT is a candidate on non-AVX512vL targets, we
    either need to check that the first operand is a register, or as done
    below provide the define_insn_and_split that provides a non-AVX512VL
    implementation of *extendv2di_highpart_stv.

    The new testcase only ICEed with -m32, so this test could be limited to
    target ia32, but there's no harm also running this test on -m64 to
    provide a little extra test coverage.

    2024-08-12  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            PR target/116275
            * config/i386/i386.md (*extendv2di2_highpart_stv_noavx512vl): New
            define_insn_and_split to handle the STV conversion of the DImode
            pattern *extendsi2_doubleword_highpart.

    gcc/testsuite/ChangeLog
            PR target/116275
            * g++.target/i386/pr116275.C: New test case.