cast lvalues optimizing and strict-aliasing

[Christian BRUEL <christian dot bruel at st dot com>]

Hello,

from my understanding of the type-punning aliasing rule, the following 
code is correct, and indeed compiles fine with gcc/trunk :

typedef struct {
  short a : 16;
  short b : 16;
} c;

foo(c t1)
{
  char *pt1 = (char*)&t1;

  if (*(int*)(pt1))
    return 0;

  return 1;
}

However if I try to rewrite it using an intermediate cast :

foo(c t1)
{
  if (*((int*)((char*)&t1)))
    return 0;

  return 1;
}

the compiler emits the "dereferencing type-punned..." warning message.

Indeed the gimple tree doesn't show the (char *) cast:

;; Function foo (null)
;; enabled by -tree-original


  if (*(int *) &t1 != 0)
    {
      return 0;
    }
  return 1;
}

And the alias analyser see the types as not-compatible. So was the 
parser allowed to ignore the (char *) cast ? I think this would change 
the aliasing semantic, but before suspecting a bug, I would very much 
like to have other opinions.

many thanks

Christian