[5614] in Athena Bugs
hc 2.1y optimizer bug
daemon@ATHENA.MIT.EDU (John Carr)
Fri Jul 27 09:40:23 1990
To: bugs@ATHENA.MIT.EDU
Date: Fri, 27 Jul 90 09:40:12 EDT
From: John Carr <jfc@ATHENA.MIT.EDU>
This function
unsigned int f(unsigned int *x)
{
while((*x++)--);
return *x;
}
compiles to this code:
_.f:
ls r0,0(r2)
L00012:
cis r0,0
inc r2,4
dec r0,1
sts r0,0(r2)
jne L00012
mr r0,r0 # no op to fix APC bug
mr r0,r0 # no op to fix APC bug
mr r0,r0 # no op to fix APC bug
brx r15
mr r2,r0
.long 0xdf02df00 #Trace table (no stack frame)
The "ls r0,0(r2)" needs to be within the loop; as compiled the loop is
equivalent to:
int y = *x;
while(*x++ = y--);
[a new version of hc2.1 is due out in a bit over a month; this should
be sent to IBM quickly if it is to affect the new version]
