4bsd-f77@utah-cs.UUCP (4.2 BSD f77 bug reports) (08/30/84)
From: Donn Seeley <donn@utah-cs.arpa>
Subject: The f77 fix for COMMON needs to be extended to EQUIVALENCE
Index: usr.bin/f77/src/f77pass1/optcse.c 4.2BSD
Description:
The fix given in 4bsd-f77 #18 (<163@sdchema.UUCP>, titled
'Revision to common subexpression bug fix in f77') is incomplete
-- the same problems that occur with common subexpressions and
COMMON variables also occur with EQUIVALENCEd variables. This
bug was observed and fixed by Jerry Berkman at UC Berkeley.
Repeat-By:
Compile the following program (from Jerry Berkman) with the
optimizer on:
----------------------------------------------------------------
c sees common subexp where none exists
double precision a0,a1, b0,b1, z0(2),z1(2)
double complex a(2), za0,za1
equivalence (za0,z0(1)),(za1,z1(1)),
1 (a0,z0(1)),(b0,z0(2)), (a1,z1(1)),(b1,z1(2))
data a/ (1.0d0,2.0d0), (12.2d0,14.8d0)/
c
za0 = a(1)
za1 = a(2)
a(1) = dcmplx(a0+a1,b0+b1)
a(2) = dcmplx(a0-a1,b0-b1)
print *, a(1), a(2)
end
----------------------------------------------------------------
When run, this program prints the following:
----------------------------------------------------------------
( 13.200000000000, 13.200000000000)
( -11.200000000000, -11.200000000000)
----------------------------------------------------------------
But it's supposed to print:
----------------------------------------------------------------
( 13.200000000000, 16.800000000000)
( -11.200000000000, -12.800000000000)
----------------------------------------------------------------
Fix:
The problem is exactly the same as the problem with COMMON
variables and CSE, except applied to EQUIVALENCEd variables; so
I will skip the usual tedious explanation and simply present
the fix. This fix applies to the routine samebase() in
f77pass1/optcse.c and must be applied AFTER the earlier fix:
----------------------------------------------------------------
*** /tmp/,RCSt1024965 Sun Aug 19 23:41:08 1984
--- optcse.c Sat Aug 4 20:39:58 1984
***************
*** 404,409
case TADDR :
if (ep1->addrblock.vstg == ep2->addrblock.vstg) {
switch(ep1->addrblock.vstg) {
case STGCOMMON:
if (ep1->addrblock.memno == ep2->addrblock.memno &&
ISCONST(ep1->addrblock.memoffset) &&
--- 409,415 -----
case TADDR :
if (ep1->addrblock.vstg == ep2->addrblock.vstg) {
switch(ep1->addrblock.vstg) {
+ case STGEQUIV:
case STGCOMMON:
if (ep1->addrblock.memno == ep2->addrblock.memno &&
ISCONST(ep1->addrblock.memoffset) &&
----------------------------------------------------------------
Donn Seeley University of Utah CS Dept donn@utah-cs.arpa
40 46' 6"N 111 50' 34"W (801) 581-5668 decvax!utah-cs!donn