[Bug tree-optimization/41834] New: Missed "may be uninitialized warning" on array reference

["rahul at icerasemi dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Using GCC 4.4.1 and the command on the following test 

gcc -O2 -Wall -Wextra

#include <stdio.h>

int foo (int b)
{
    int a[10], c, i; 

    for (i = 0; i < b; i++)
    {
        a[i] = b;
        c = b;
    }

    if (a[2] == 5 && c == 5)
    {
        printf("hello world\n");
    }
    return 0;
}

testWarn.c: In function 'foo': testWarn.c:5: warning: 'c' may be used
uninitialized in this function 

However, a warning for a[2] being possibly uninitialized is missing.

If I understand right, this should be handled by late warning pass which just
after DCE. Looking at post DCE dump

foo (int b)
{
  unsigned int D.1282;
  int i;
  int c;
  int a[10];
  _Bool D.1243;
  _Bool D.1242;
  _Bool D.1241;
  int D.1240;

<bb 2>:
  if (b_5(D) > 0)
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 3>:
  # i_21 = PHI <0(2), i_8(3)>
  D.1282_25 = (unsigned int) i_21;
  MEM[base: &a, index: D.1282_25, step: 4] = b_5(D);
  i_8 = i_21 + 1;
  if (i_8 != b_5(D))
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 4>:
  # c_17 = PHI <b_5(D)(3), c_4(D)(2)>
  D.1240_9 = a[2];
  D.1241_10 = D.1240_9 == 5;
  D.1242_11 = c_17 == 5;
  D.1243_12 = D.1242_11 & D.1241_10;
  if (D.1243_12 != 0)
    goto <bb 5>;
  else
    goto <bb 6>;

<bb 5>:
  __builtin_puts (&"hello world"[0]);

<bb 6>:
  return 0;

}

there is a path to bb 4, which does not initialize a. Why do we not generate a
warning? Is it due a missing PHI for a?


-- 
           Summary: Missed "may be uninitialized warning" on array reference
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rahul at icerasemi dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41834