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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/99473] New: redundant conditional
 zero-initialization not eliminated
Date: Mon, 08 Mar 2021 20:24:43 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 11.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99473

            Bug ID: 99473
           Summary: redundant conditional zero-initialization not
                    eliminated
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

All three functions below should result in equivalently optimal code (and,
ideally IL) but only g1() and g3() result in the same assembly, and only g1=
()
result in optimal, branchless GIMPLE.

$ cat x.c && gcc -O2 -S -Wall -o/dev/stdout x.c
void f (int*);

void g1 (int i)
{
  int x;
  if (i)
    x =3D i;
  else
    x =3D 0;
  f (&x);
}


void g2 (int i)
{
  int x;
  if (i) {
    x =3D i;
    f (&x);
  }
  else {
    x =3D 0;
    f (&x);
  }
}

void g3 (int i)
{
  int x =3D 0;
  if (i)
    x =3D i;
  f (&x);
}
        .file   "x.c"
        .text
        .p2align 4
        .globl  g1
        .type   g1, @function
g1:
.LFB0:
        .cfi_startproc
        subq    $24, %rsp
        .cfi_def_cfa_offset 32
        movl    %edi, 12(%rsp)
        leaq    12(%rsp), %rdi
        call    f
        addq    $24, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc
.LFE0:
        .size   g1, .-g1
        .p2align 4
        .globl  g2
        .type   g2, @function
g2:
.LFB1:
        .cfi_startproc
        subq    $24, %rsp
        .cfi_def_cfa_offset 32
        testl   %edi, %edi
        je      .L5
        movl    %edi, 12(%rsp)
        leaq    12(%rsp), %rdi
        call    f
        addq    $24, %rsp
        .cfi_remember_state
        .cfi_def_cfa_offset 8
        ret
        .p2align 4,,10
        .p2align 3
.L5:
        .cfi_restore_state
        leaq    12(%rsp), %rdi
        movl    $0, 12(%rsp)
        call    f
        addq    $24, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc
.LFE1:
        .size   g2, .-g2
        .p2align 4
        .globl  g3
        .type   g3, @function
g3:
.LFB2:
        .cfi_startproc
        subq    $24, %rsp
        .cfi_def_cfa_offset 32
        movl    %edi, 12(%rsp)
        leaq    12(%rsp), %rdi
        call    f
        addq    $24, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc
.LFE2:
        .size   g3, .-g3
        .ident  "GCC: (GNU) 11.0.1 20210308 (experimental)"
        .section        .note.GNU-stack,"",@progbits=