[Bug middle-end/54804] -Wuninitialized fails to warn about uninitialized local union

["manu at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54804

Manuel LÃpez-IbÃÃez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-10-04
                 CC|                            |manu at gcc dot gnu.org
          Component|c                           |middle-end
             Blocks|                            |24639
     Ever Confirmed|0                           |1

--- Comment #1 from Manuel LÃpez-IbÃÃez <manu at gcc dot gnu.org> 2012-10-04 08:07:35 UTC ---
Confirmed. early SRA creates a scalar replacement for the struct but not for
the union:

;; Function yyparse (yyparse, funcdef_no=0, decl_uid=1710, cgraph_uid=0)
yyparse ()
{
  union YYSTYPE yylval;
  union YYSTYPE D.1720;

<bb 2>:
  [pr54804.c : 6:6] D.1720 = yylval;
  yylval ={v} {CLOBBER};
  [pr54804.c : 6:6] return D.1720;
}
;; Function yyparse_with_struct (yyparse_with_struct, funcdef_no=1,
decl_uid=1716, cgraph_uid=1)

Created a replacement for xxlval offset: 0, size: 32: xxlval$ival

Symbols to be put in SSA form
{ xxlval$ival }
Incremental SSA update started at block: 0
Number of blocks in CFG: 3
Number of blocks to update: 2 ( 67%)


yyparse_with_struct ()
{
  int xxlval$ival;
  struct s xxlval;
  struct s D.1723;

<bb 2>:
  [pr54804.c : 15:6] [pr54804.c : 15] MEM[(struct s *)&D.1723] =
xxlval$ival_3(D);
  [pr54804.c : 15:6] return D.1723;
}

Alternatively, one may see the problem as Wuninitialized not working with
anything that leaves in memory (structs/union/arrays) unless SRA is applied.
There are a few PRs about that.