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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/112494] ICE in ix86_cc_mode, at
 config/i386/i386.cc:16477
Date: Mon, 13 Nov 2023 21:47:54 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112494

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Uros Bizjak <uros@gcc.gnu.org>:

https://gcc.gnu.org/g:c75bab7274fe60fb2def8acf06ee9f4f856ce1ac

commit r14-5419-gc75bab7274fe60fb2def8acf06ee9f4f856ce1ac
Author: Uros Bizjak <ubizjak@gmail.com>
Date:   Mon Nov 13 22:45:55 2023 +0100

    i386: Return CCmode from ix86_cc_mode for unknown RTX code [PR112494]

    Combine wants to combine following instructions into an insn that can
    perform both an (arithmetic) operation and set the condition code.  Dur=
ing
    the conversion a new RTX is created, and combine passes the RTX code of=
 the
    innermost RTX expression of the CC use insn in which CC reg is used to
    SELECT_CC_MODE, to determine the new mode of the comparison:

    Trying 5 -> 8:
        5: r98:DI=3D0xd7
        8: flags:CCZ=3Dcmp(r98:DI,0)
          REG_EQUAL cmp(0xd7,0)
    Failed to match this instruction:
    (parallel [
            (set (reg:CC 17 flags)
                (compare:CC (const_int 215 [0xd7])
                    (const_int 0 [0])))
            (set (reg/v:DI 98 [ flags ])
                (const_int 215 [0xd7]))
        ])

    where:

    (insn 5 2 6 2 (set (reg/v:DI 98 [ flags ])
            (const_int 215 [0xd7])) "pr112494.c":8:8 84 {*movdi_internal}
         (nil))

    (insn 8 7 11 2 (set (reg:CCZ 17 flags)
            (compare:CCZ (reg/v:DI 98 [ flags ])
                (const_int 0 [0]))) "pr112494.c":11:9 8 {*cmpdi_ccno_1}
         (expr_list:REG_EQUAL (compare:CCZ (const_int 215 [0xd7])
                (const_int 0 [0]))
            (nil)))

    x86_cc_mode (AKA SELECT_CC_MODE) is not prepared to handle random RTX
    codes and triggers gcc_unreachable() when SET RTX code is passed to it.
    The patch removes gcc_unreachable() and returns CCmode for unknown
    RTX codes, so combine can try various combinations involving CC reg
    without triggering ICE.

    Please note that x86 MOV instructions do not set flags, so the above
    combination is not recognized as a valid x86 instruction.

            PR target/112494

    gcc/ChangeLog:

            * config/i386/i386.cc (ix86_cc_mode) [default]: Return CCmode.

    gcc/testsuite/ChangeLog:

            * gcc.target/i386/pr112494.c: New test.=