chris@umcp-cs.UUCP (Chris Torek) (11/18/84)
Index: lib/pcc/optim.c 4.2 Fix
Description:
The machine independent expression optimizer doesn't handle
"/=", "%", or "%=" by the constants 1 and 0.
Repeat-By:
Feed the following through /lib/ccom; look at the assembly:
f () {
register i,j;
i = j / 1; /* nice, the division goes away */
i /= 1; /* but not this time! */
i = j % 1; /* result is always 0, but talk
about doing things the hard way */
i %= 1; /* same */
}
Fix:
The following changes to optim.c make it like /= as well as /,
and make it handle % 1 and %= 1 in a reasonable way. We also
added checks for division and mod by zero (they used to just
generate divisions by zero).
RCS file: RCS/optim.c,v
retrieving revision 1.1
diff -c1 -r1.1 optim.c
*** /tmp/,RCSt1008671 Sun Nov 18 07:16:07 1984
--- optim.c Sun Nov 18 07:15:44 1984
***************
*** 142,143
case DIV:
--- 142,157 -----
+ case ASG MOD:
+ case MOD:
+ if( nncon( p->in.right ) ){
+ if( p->in.right->tn.lval == 1 ){
+ /* mod by one gives zero */
+ p->in.op = p->in.op==MOD ? COMOP : ASSIGN;
+ p->in.right->tn.lval = 0;
+ break;
+ }
+ if( p->in.right->tn.lval == 0 ) uerror("mod by zero");
+ }
+ break;
+
+ case ASG DIV:
case DIV:
***************
*** 143,145
case DIV:
! if( nncon( p->in.right ) && p->in.right->tn.lval == 1 ) goto zapright;
break;
--- 157,162 -----
case DIV:
! if( nncon( p->in.right ) ){
! if( p->in.right->tn.lval == 1 ) goto zapright;
! if( p->in.right->tn.lval == 0 ) uerror("division by zero");
! }
break;
--
(This line accidently left nonblank.)
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (301) 454-7690
UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet: chris@umcp-cs ARPA: chris@maryland