[Bug tree-optimization/24931] [4.0/4.1 Regression] uninitialized structure member after assignment

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

------- Comment #1 from pinskia at gcc dot gnu dot org  2005-11-18 06:19 -------
First this is a very bogus warning.
Second this is caused by SRA and BIT_FIELD_REF:
  D.1509.x = 0;
  D.1509.y = 0;
  s.p = D.1509;
  D.1511_10 = BIT_FIELD_REF <s, 32, 32>;
  D.1512_12 = D.1511_10 != 0;
  s.i = D.1512_12;
  D.1513 = s;

The problem is that SRA does not look into seeing if s.i is needed so it does:
  SR.25_11 = 0;
  SR.24_26 = 0;
  s$p$y_27 = SR.24_26;
  s$p$x_28 = SR.25_11;
  s.i = s$i_29;
  s.p.y = s$p$y_27;
  s.p.x = s$p$x_28;
  D.1511_10 = BIT_FIELD_REF <s, 32, 32>;
  D.1512_12 = D.1511_10 != 0;
  s$i_33 = D.1512_12;
  s.i = s$i_33;
  s.p.y = s$p$y_27;
  s.p.x = s$p$x_28;
  D.1513 = s;

The wrong code part is not really wrong code, just a misunderstanding of what
the instruction does:
(insn 43 40 49 (set (reg/i:DI 0 ax [ <result> ]) 
        (const_int 0 [0x0])) 81 {*movdi_1_rex64} (insn_list:REG_DEP_TRUE 35
(nil))
    (nil))

It sign extends to the full register which means rax is 0 and not just the
bottom part.

Hmm, even the struct aliasing code does not know either:
  #   VUSE <SFT.3_7>;
  #   VUSE <SFT.4_8>;
  #   VUSE <SFT.5_9>;
  D.1511_10 = BIT_FIELD_REF <s, 32, 32>;


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rth at gcc dot gnu dot org,
                   |                            |dberlin at gcc dot gnu dot
                   |                            |org
OtherBugsDependingO|                            |24639
              nThis|                            |
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|x86_64-pc-linux-gnu         |
   GCC host triplet|x86_64-pc-linux-gnu         |
 GCC target triplet|x86_64-pc-linux-gnu         |x86_64-*-* i?86-*-*
   Last reconfirmed|0000-00-00 00:00:00         |2005-11-18 06:19:39
               date|                            |
            Summary|uninitialized structure     |[4.0/4.1 Regression]
                   |member after assignment     |uninitialized structure
                   |                            |member after assignment
   Target Milestone|---                         |4.0.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24931