[Bug middle-end/34678] Optimization generates incorrect code with -frounding-math option (#pragma STDC FENV_ACCESS not implemented)

["vincent-gcc at vinc17 dot net" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34678

--- Comment #24 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Nick Maclaren from comment #23)
> If __STDC_IEC_559__ is unset or does not have the value 1, setting
> STDC FENV_ACCESS to "on" is undefined behaviour (see 6.10.8.3, 7.6 and
> Annex F), unless the implementation explicitly chooses to extend the
> language to support it.

You're wrong. The C standard doesn't say that.

6.10.8.3 says: "__STDC_IEC_559__ The integer constant 1, intended to indicate
conformance to the specifications in annex F (IEC 60559 floating-point
arithmetic)." and nothing about STDC FENV_ACCESS.

In 7.6, only 7.6.1 is specifically about the FENV_ACCESS pragma, and it
specifies under which conditions the behavior is undefined, but nothing related
to __STDC_IEC_559__ and Annex F.

Annex F doesn't apply in the case __STDC_IEC_559__ is unset.
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Subject: [Bug c/59755] BUG Increment Operator with Accessing Arrays
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59755

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |trippels at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #2 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
With -Wall one gets:
test.c: In function ‘main’:
test.c:12:14: warning: operation on ‘m’ may be undefined [-Wsequence-point]
  D = A[m][B[m++]];
              ^

Thus your testcase is invalid because of unsequenced modification
and access to m.
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Subject: [Bug middle-end/59743] [4.9 Regression] ICE: Segmentation fault
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idY743

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ah, there is:
  /* If the df_live problem is not defined, such as at -O0 and -O1, we
     still need to keep the luids up to date.  This is normally done
     in the df_live problem since this problem has a forwards
     scan.  */
  if (!df_live)
    df_recompute_luids (bb);
in df_lr_bb_local_compute, so I think luids are fine even at -O0/-O1.