This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
Re: optimization/5244: Dead code in simplify_logical()
- From: Craig Rodrigues <rodrigc at mediaone dot net>
- To: gcc-gnats at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, Kai dot Tietz at onevision dot de, gcc-bugs at gcc dot gnu dot org, nobody at gcc dot gnu dot org
- Date: Mon, 28 Jan 2002 23:06:21 -0500
- Subject: Re: optimization/5244: Dead code in simplify_logical()
In PR 5244:
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5244
you submitted a patch, which I have reproduced here
in unified context diff format. Can you explain
why this patch is necessary? I did not
understand your explanation.
Index: combine.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/combine.c,v
retrieving revision 1.183.2.8
diff -u -r1.183.2.8 combine.c
--- combine.c 2001/11/05 19:10:32 1.183.2.8
+++ combine.c 2002/01/29 03:58:03
@@ -5391,8 +5391,25 @@
If we have (and (ior A B) C), apply the distributive law and then
the inverse distributive law to see if things simplify. */
+ /* Similarly, taking advantage of the fact that
+ (and (not A) (xor B C)) == (xor (ior A B) (ior A C)) */
+
+ if (GET_CODE (op0) == NOT && GET_CODE (op1) == XOR)
+ return apply_distributive_law
+ (gen_binary (XOR, mode,
+ gen_binary (IOR, mode, XEXP (op0, 0), XEXP (op1, 0)),
+ gen_binary (IOR, mode, copy_rtx (XEXP (op0, 0)),
+ XEXP (op1, 1))));
+
+ else if (GET_CODE (op1) == NOT && GET_CODE (op0) == XOR)
+ return apply_distributive_law
+ (gen_binary (XOR, mode,
+ gen_binary (IOR, mode, XEXP (op1, 0), XEXP (op0, 0)),
+ gen_binary (IOR, mode, copy_rtx (XEXP (op1, 0)), XEXP (op0, 1))));
+
if (GET_CODE (op0) == IOR || GET_CODE (op0) == XOR)
{
+ /* ??? May we get better code, if we do this optimization anyway */
x = apply_distributive_law
(gen_binary (GET_CODE (op0), mode,
gen_binary (AND, mode, XEXP (op0, 0), op1),
@@ -5409,21 +5426,6 @@
gen_binary (AND, mode, XEXP (op1, 1),
copy_rtx (op0))));
- /* Similarly, taking advantage of the fact that
- (and (not A) (xor B C)) == (xor (ior A B) (ior A C)) */
-
- if (GET_CODE (op0) == NOT && GET_CODE (op1) == XOR)
- return apply_distributive_law
- (gen_binary (XOR, mode,
- gen_binary (IOR, mode, XEXP (op0, 0), XEXP (op1, 0)),
- gen_binary (IOR, mode, copy_rtx (XEXP (op0, 0)),
- XEXP (op1, 1))));
-
- else if (GET_CODE (op1) == NOT && GET_CODE (op0) == XOR)
- return apply_distributive_law
- (gen_binary (XOR, mode,
- gen_binary (IOR, mode, XEXP (op1, 0), XEXP (op0, 0)),
- gen_binary (IOR, mode, copy_rtx (XEXP (op1, 0)), XEXP (op0, 1))));
break;
case IOR:
--
Craig Rodrigues
http://www.gis.net/~craigr
rodrigc@mediaone.net