[Bug inline-asm/68084] New: Inverted conditions generated for x86 inline assembly "flag output constraints"

[Bug inline-asm/68084] New: Inverted conditions generated for x86 inline assembly "flag output constraints"

[richardpku at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68084

            Bug ID: 68084
           Summary: Inverted conditions generated for x86 inline assembly
                    "flag output constraints"
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richardpku at gmail dot com
  Target Milestone: ---

I have been trying out the new "flag output constraints" feature in inline
assembly ("=@ccCC"), and have found GCC sometimes incorrectly generates
inverted conditions in assembler code.

The minimal test case is as follows:


_Bool dec_ref(unsigned *p)
{
  _Bool r;
  asm ("cmp %2, %1" : "=@ccae"(r) : "m"(*p), "ri"(2));
  if (r)
    return __atomic_sub_fetch(p, 1, __ATOMIC_RELEASE) == 0;
  return 1;
}


GCC (6.0.0 20151024) generates the following assembler code:


dec_ref:
        cmp $2, (%rdi)
        movl    $1, %eax
        jc      .L7
        rep ret
        .p2align 4,,10
        .p2align 3
.L7:
        lock subl       $1, (%rdi)
        sete    %al
        ret


where "jc" is incorrect. It should be "jnc".

Interestingly, GCC generates the expected code if "=@ccae" is written as
"=@ccnb" (ae and nb are synonymous).

[Bug inline-asm/68084] Inverted conditions generated for x86 inline assembly "flag output constraints"

[gccbugzilla at limegreensocks dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68084

David <gccbugzilla at limegreensocks dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gccbugzilla@limegreensocks.
                   |                            |com

--- Comment #1 from David <gccbugzilla at limegreensocks dot com> ---
Created attachment 36580
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36580&action=edit
Possible fix

As I read the code, I think the logic for 'ae' is just backwards.  Try this.

[Bug inline-asm/68084] Inverted conditions generated for x86 inline assembly "flag output constraints"

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68084

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-10-25
           Assignee|unassigned at gcc dot gnu.org      |ubizjak at gmail dot com
   Target Milestone|---                         |6.0
     Ever confirmed|0                           |1

--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> ---
Oh, indeed.

I'll fix this in a moment.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idh084

--- Comment #3 from uros at gcc dot gnu.org ---
Author: uros
Date: Sun Oct 25 13:21:01 2015
New Revision: 229296

URL: https://gcc.gnu.org/viewcvs?rev"9296&root=gcc&view=rev
Log:
        PR target/68084
        * config/i386/i386.c (ix86_md_asm_adjust) [case 'a']: Use NE code
        for =@ccae.

testsuite/ChangeLog:

        PR target/68084
        * gcc.target/i386/pr68084.c: New test.


Added:
    trunk/gcc/testsuite/gcc.target/i386/pr68084.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/i386/i386.c
    trunk/gcc/testsuite/ChangeLog

[Bug inline-asm/68084] Inverted conditions generated for x86 inline assembly "flag output constraints"

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68084

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Uroš Bizjak <ubizjak at gmail dot com> ---
Fixed.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idh078

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|2015-10-24 00:00:00         |2015-10-25
     Ever confirmed|0                           |1

--- Comment #1 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Confirmed from 4.8 up to trunk (6.0). Duplicate of pr59796?