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From: "scherrer.sv at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110991] New: [14 Regression] Dead Code
 Elimination Regression at -O2 since r14-1135-gc53f51005de
Date: Fri, 11 Aug 2023 13:08:42 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110991

            Bug ID: 110991
           Summary: [14 Regression] Dead Code Elimination Regression at
                    -O2 since r14-1135-gc53f51005de
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: scherrer.sv at gmail dot com
  Target Milestone: ---

static unsigned char a;
static char b;
void foo(void);
int main() {
  a =3D 25;
  for (; a > 13; --a)
    b =3D a > 127 ?: a << 3;
  if (!b)
    foo();
}

gcc-3a13884b23a (trunk) -O2 cannot eliminate the call to foo but
gcc-releases/gcc-13.1.0 -O2 can.
-----------------------------------------------------------------------
gcc-3a13884b23ae32b43d56d68a9c6bd4ce53d60017 -O2 case.c -S -o case.s
--------- OUTPUT ---------
main:
.LFB0:
        .cfi_startproc
        movd    .LC0(%rip), %xmm0
        movd    .LC1(%rip), %xmm1
        xorl    %eax, %eax
.L2:
        addl    $1, %eax
        movdqa  %xmm0, %xmm2
        paddb   %xmm1, %xmm0
        cmpl    $3, %eax
        jne     .L2
        movdqa  %xmm2, %xmm0
        movb    $13, a(%rip)
        paddb   %xmm2, %xmm0
        paddb   %xmm0, %xmm0
        movdqa  %xmm0, %xmm1
        paddb   %xmm0, %xmm1
        pxor    %xmm0, %xmm0
        pcmpgtb %xmm2, %xmm0
        movd    .LC2(%rip), %xmm2
        pand    %xmm0, %xmm2
        pandn   %xmm1, %xmm0
        por     %xmm2, %xmm0
        movd    %xmm0, %eax
        sarl    $24, %eax
        movb    %al, b(%rip)
        testb   %al, %al
        je      .L10
        xorl    %eax, %eax
        ret
.L10:
        pushq   %rax
        .cfi_def_cfa_offset 16
        call    foo
        xorl    %eax, %eax
        popq    %rdx
        .cfi_def_cfa_offset 8
        ret
---------- END OUTPUT ---------

-----------------------------------------------------------------------
gcc-2b98cc24d6af0432a74f6dad1c722ce21c1f7458 -O2 case.c -S -o case.s
--------- OUTPUT ---------
main:
.LFB0:
        .cfi_startproc
        movb    $112, b(%rip)
        xorl    %eax, %eax
        movb    $13, a(%rip)
        ret
---------- END OUTPUT ---------

-----------------------------------------------------------------------
Bisects to r14-1135-gc53f51005de=