[Bug target/99234] [10/11 regression] wrong result for 1.0/3.0 with -O2 -fno-omit-frame-pointer -frounding-math

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99234

--- Comment #27 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Eric Botcazou <ebotcazou@gcc.gnu.org>:

https://gcc.gnu.org/g:e8d1ca7d2c344a411779892616c423e157f4aea8

commit r12-525-ge8d1ca7d2c344a411779892616c423e157f4aea8
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Wed May 5 22:48:51 2021 +0200

    Fix PR target/100402

    This is a regression for 64-bit Windows present from mainline down to the 9
    branch and introduced by the fix for PR target/99234.  Again SEH, but with
    a twist related to the way MinGW implements setjmp/longjmp, which turns out
    to be piggybacked on SEH with recent versions of MinGW, i.e. the longjmp
    performs a bona-fide unwinding of the stack, because it calls RtlUnwindEx
    with the second argument initially passed to setjmp, which is the result of
    __builtin_frame_address (0) in the MinGW header file:

      define setjmp(BUF) _setjmp((BUF), __builtin_frame_address (0))

    This means that we directly expose the frame pointer to the SEH machinery
    here (unlike with regular exception handling where we use an intermediate
    CFA) and thus that we cannot do whatever we want with it.  The old code
    would leave it unaligned, i.e. not multiple of 16, whereas the new code
    aligns it, but this breaks for some reason; at least it appears that a
    .seh_setframe directive with 0 as second argument always works, so the
    fix aligns it this way.

    gcc/
            PR target/100402
            * config/i386/i386.c (ix86_compute_frame_layout): For a SEH target,
            always return the establisher frame for __builtin_frame_address
(0).
    gcc/testsuite/
            * gcc.c-torture/execute/20210505-1.c: New test.