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Subject: [Bug target/50131] New: Optimize x = -1 with "or" for -O
Date: Fri, 19 Aug 2011 20:58:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50131

             Bug #: 50131
           Summary: Optimize x = -1 with "or" for -O
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hjl.tools@gmail.com
                CC: ubizjak@gmail.com


[hjl@gnu-6 rtm-1]$ cat x.c
int
foo1 ()
{
  return -1;
}

short
foo2 ()
{
  return -1;
}

long long
foo3 ()
{
  return -1;
}
[hjl@gnu-6 rtm-1]$ gcc -S -Os x.c 
[hjl@gnu-6 rtm-1]$ cat x.s
    .file    "x.c"
    .text
    .globl    foo1
    .type    foo1, @function
foo1:
.LFB0:
    .cfi_startproc
    orl    $-1, %eax
    ret
    .cfi_endproc
.LFE0:
    .size    foo1, .-foo1
    .globl    foo2
    .type    foo2, @function
foo2:
.LFB1:
    .cfi_startproc
    orl    $-1, %eax
    ret
    .cfi_endproc
.LFE1:
    .size    foo2, .-foo2
    .globl    foo3
    .type    foo3, @function
foo3:
.LFB2:
    .cfi_startproc
    orq    $-1, %rax
    ret
    .cfi_endproc
.LFE2:
    .size    foo3, .-foo3
    .ident    "GCC: (GNU) 4.6.0 20110603 (Red Hat 4.6.0-10)"
    .section    .note.GNU-stack,"",@progbits
[hjl@gnu-6 rtm-1]$ gcc -S -O2 x.c 
[hjl@gnu-6 rtm-1]$ cat x.s
    .file    "x.c"
    .text
    .p2align 4,,15
    .globl    foo1
    .type    foo1, @function
foo1:
.LFB0:
    .cfi_startproc
    movl    $-1, %eax
    ret
    .cfi_endproc
.LFE0:
    .size    foo1, .-foo1
    .p2align 4,,15
    .globl    foo2
    .type    foo2, @function
foo2:
.LFB1:
    .cfi_startproc
    movl    $-1, %eax
    ret
    .cfi_endproc
.LFE1:
    .size    foo2, .-foo2
    .p2align 4,,15
    .globl    foo3
    .type    foo3, @function
foo3:
.LFB2:
    .cfi_startproc
    movq    $-1, %rax
    ret
    .cfi_endproc
.LFE2:
    .size    foo3, .-foo3
    .ident    "GCC: (GNU) 4.6.0 20110603 (Red Hat 4.6.0-10)"
    .section    .note.GNU-stack,"",@progbits
[hjl@gnu-6 rtm-1]$ 

I was expecting "or" for -O.