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From: "yann at ywg dot ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108360] New: Dead Code Elimination Regression
 at -Os (trunk vs. 12.2.0)
Date: Tue, 10 Jan 2023 13:10:43 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108360

            Bug ID: 108360
           Summary: Dead Code Elimination Regression at -Os (trunk vs.
                    12.2.0)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yann at ywg dot ch
  Target Milestone: ---

Created attachment 54235
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D54235&action=3Dedit
case.c as file

cat case.c #321
static short b, c;
unsigned char e;
char f;
void foo();
short(a)(short h, short i) { return h + i; }
static short(d)(short h, int i) { return h >=3D 32 || h > 7 >> i ? h : h <<=
 i; }
unsigned g(short h, short i) { return h + i; }
int main() {
  short j, k =3D -1;
  c =3D a(0 >=3D b, k);
  f =3D c <=3D 0xD315BEF1;
  e =3D f << 4;
  j =3D d(e, 5);
  if (3 >=3D g(j =3D=3D b, k))
    foo();
  b =3D 0;
}

`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -Os` can not eliminate
`foo` but `gcc-releases/gcc-12.2.0 -Os` can.

`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -Os -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB3:
        .cfi_startproc
        movw    b(%rip), %cx
        xorl    %edx, %edx
        testw   %cx, %cx
        setle   %dl
        movl    %edx, %eax
        movb    %dl, f(%rip)
        sall    $4, %eax
        movb    %al, e(%rip)
        movzbl  %al, %eax
        testw   %dx, %dx
        jne     .L4
        sall    $5, %eax
.L4:
        cmpw    %ax, %cx
        jne     .L7
        pushq   %rax
        .cfi_def_cfa_offset 16
        xorl    %eax, %eax
        call    foo
        xorl    %eax, %eax
        movw    $0, b(%rip)
        popq    %rdx
        .cfi_def_cfa_offset 8
        ret
.L7:
        movw    $0, b(%rip)
        xorl    %eax, %eax
        ret
---------- END OUTPUT ---------


`gcc-releases/gcc-12.2.0 -Os -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB3:
        .cfi_startproc
        xorl    %eax, %eax
        cmpw    $0, b(%rip)
        movw    $0, b(%rip)
        setle   %al
        movb    %al, f(%rip)
        sall    $4, %eax
        movb    %al, e(%rip)
        xorl    %eax, %eax
        ret
---------- END OUTPUT ---------


Bisects to:
https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dcommit;h=3D418b71c0d535bf91df78bad=
2e198c57934682eaa=