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From: "sebastien.michelland@ens-lyon.fr" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/106609] [SH] miscompilation due to incorrect elimination
 of comparisons to 0
Date: Tue, 16 Aug 2022 21:03:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106609

S=C3=A9bastien Michelland <sebastien.michelland@ens-lyon.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[SH] miscompilation of loop |[SH] miscompilation due to
                   |involving noreturn call     |incorrect elimination of
                   |                            |comparisons to 0

--- Comment #4 from S=C3=A9bastien Michelland <sebastien.michelland@ens-lyo=
n.fr> ---
> Then this is a target specific issue until provided otherwise. mach stand=
s for machine (target) specific pass.

That makes a lot of sense, thanks.

I found a much simpler example exhibiting the bug:

int f(int i, int j)
{
    if(i < 0) return 1;
    if(i + j) return 3;
    return i;
}

Latest HEAD with -O1 (same setup as before) compiles it to

_f:     cmp/pz  r4
        bf      .L3
        bf      .L4
        rts=20=20=20=20=20
        mov     r4,r0
.L3:    rts=20=20=20=20=20
        mov     #1,r0
.L4:    rts=20=20=20=20=20
        mov     #3,r0

incorrectly eliminating the test for (i + j) !=3D 0. The label .L4 returnin=
g 3 is
evidently unreachable.

Comparing to 0 seems to be required. My previous example also compiles
correctly if we check values[i] !=3D 1 instead, which invalidates the loop/=
CFG
theory.

Few commits changed the SH subtree since GCC 11.1.0; I should be able to bi=
sect
it. In the meantime I've updated the title.=