Re: Uninitialized variable warnings

[Jeffrey A Law <law at upchuck dot cygnus dot com>]

  In message <199903160417.XAA29108@blastula.phys.columbia.edu>you write:
  > >This is pretty straightforward setting hi in both arms of an if-else
  > >or even unconditionally in each of the disjoint lifetimes.
  > 
  >     case ADDR_EXPR:
  >       {
  >         struct addr_const value;
  > 
  >         decode_addr_const (exp, &value);
  >         if (GET_CODE (value.base) == SYMBOL_REF)
  >           {
  >             /* Don't hash the address of the SYMBOL_REF;
  >                only use the offset and the symbol name.  */
  >             hi = value.offset;
  >             p = XSTR (value.base, 0);
  >             for (i = 0; p[i] != 0; i++)
  >               hi = ((hi * 613) + (unsigned) (p[i]));
  >           }
  >         else if (GET_CODE (value.base) == LABEL_REF)
  >           hi = value.offset + CODE_LABEL_NUMBER (XEXP (value.base, 0)) * 13
  > ;
  > 
  > 	hi &= (1 << HASHBITS) - 1;
  > 
  > If GET_CODE (value.base) is not SYMBOL_REF or LABEL_REF, hi is used
  > unintialized.  Maybe that never happens with correct RTL, but we ought
  > at least to have an `else abort()' in there.  I considered all the
  > cases like this to be real bugs.
Adding an else abort () seems quite reasonable to me.  If it ever triggers
we've got a real bug to track down.

These are precisely the kinds of things we need to spend time looking at --
no -W flag will ever know enough about the semantics of this code to determine
whether or not the variable can be used without being set.

jeff