[Bug c++/61872] Assigning to "long double" causes memset to be improperly elided

[Bug c++/61872] Assigning to "long double" causes memset to be improperly elided

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61872

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-07-23
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed, mine.

int main()
{
  long double a;
  __builtin_memset(&a, '\0', sizeof(long double));
  a = 1.0;

  long double b;
  __builtin_memset(&b, '\0', sizeof(long double));
  b = 1.0;

  if (__builtin_memcmp(&a, &b, sizeof(long double)))
    __builtin_abort ();
  return 0;
}

[Bug target/61872] Assigning to "long double" causes memset to be improperly elided

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61872

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Old value = 12 '\f'
New value = 16 '\020'
init_adjust_machine_modes () at insn-modes.c:1069
1066      /* config/i386/i386-modes.def:34 */
1067      s = TARGET_128BIT_LONG_DOUBLE ? 16 : 12;
1068      mode_size[XFmode] = s;
1069      mode_base_align[XFmode] = s & (~s + 1);

/* In ILP32 mode, XFmode has size 12 and alignment 4.
   In LP64 mode, XFmode has size and alignment 16.  */
ADJUST_FLOAT_FORMAT (XF, (TARGET_128BIT_LONG_DOUBLE
                          ? &ieee_extended_intel_128_format
                          : TARGET_96_ROUND_53_LONG_DOUBLE
                          ? &ieee_extended_intel_96_round_53_format
                          : &ieee_extended_intel_96_format));

ok, but with that you need to adjust the insns to actually store 16bits.

Target bug.

[Bug target/61872] Assigning to "long double" causes memset to be improperly elided

[ch3root at openwall dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61872

Alexander Cherepanov <ch3root at openwall dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ch3root at openwall dot com

--- Comment #4 from Alexander Cherepanov <ch3root at openwall dot com> ---
This looks like a dup of pr93270, so:
- this is invalid because assignments can change padding;
- this is probably fixed together with pr94103.

[Bug target/61872] Assigning to "long double" causes memset to be improperly elided

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61872

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Indeed this one is invalid, the padding becomes undefined after the
long double store.

*** This bug has been marked as a duplicate of bug 93270 ***