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From: "acoplan at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/99748] New: MVE: Wrong code at -O0 with float to integer
 conversion
Date: Wed, 24 Mar 2021 10:04:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99748

            Bug ID: 99748
           Summary: MVE: Wrong code at -O0 with float to integer
                    conversion
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: acoplan at gcc dot gnu.org
  Target Milestone: ---

GCC miscompiles the following testcase:

int main() {
  float a =3D 1.0f;
  return (int)a !=3D 1;
}

with -march=3Darmv8.1-m.main+mve -mfloat-abi=3Dhard. The program should ret=
urn 0
but returns 1 when compiled with these options. Looking at the generated co=
de:

main:
        @ args =3D 0, pretend =3D 0, frame =3D 8
        @ frame_needed =3D 1, uses_anonymous_args =3D 0
        push    {r7, lr}
        sub     sp, sp, #8
        add     r7, sp, #0
        mov     r3, #1065353216
        str     r3, [r7, #4]    @ float
        vldr.32 s0, [r7, #4]
        bl      __aeabi_f2iz
        mov     r3, r0
        cmp     r3, #1
        ite     ne
        movne   r3, #1
        moveq   r3, #0
        uxtb    r3, r3
        mov     r0, r3
        adds    r7, r7, #8
        mov     sp, r7
        @ sp needed
        pop     {r7, pc}
        .size   main, .-main

we use the aeabi_f2iz libcall to do the float to integer conversion, passing
the argument in the s0 (VFP) register. However, looking at the implementati=
on
of aeabi_f2iz in libgcc/config/arm/ieee754-sf.S, the function appears to be
expecting its argument in the GPR r0. So we do the conversion on whatever
happens to be in r0 when the libcall is made.=