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* [Bug c/16632] New: A couple fold-const.c optimizations are non-functional
@ 2004-07-19 18:05 trt at acm dot org
2004-07-19 18:35 ` [Bug tree-optimization/16632] " pinskia at gcc dot gnu dot org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: trt at acm dot org @ 2004-07-19 18:05 UTC (permalink / raw)
To: gcc-bugs
In fold-const.c there are a couple of bitmask/comparision optimizations:
/* If we have (A & C) == D where D & ~C != 0, convert this into 0.
and
/* If we have (A | C) == D where C & ~D != 0, convert this into 0.
Sample C code:
void subr (int i)
{
if ((i|3) == 1) return; /* never taken */
if ((i&4) == 2) return; /* never taken */
}
Unfortunately fold-const.c neglects to fold ~C (~D) and so
the detection of these cases is non-functional.
I'm not sure how to demonstrate this outside the debugger,
since later pieces of gcc seem to clean this up.
For example ~D is computed on approx line 8391 with
build1 (BIT_NOT_EXPR, TREE_TYPE (arg1), arg1)));
This should be fold(build1 ...), or fold_not_const(arg1, TREE_TYPE(arg1)).
Similarly for ~C on approx line 8373.
--
Summary: A couple fold-const.c optimizations are non-functional
Product: gcc
Version: 3.5.0
Status: UNCONFIRMED
Severity: minor
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: trt at acm dot org
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/16632] A couple fold-const.c optimizations are non-functional
2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
@ 2004-07-19 18:35 ` pinskia at gcc dot gnu dot org
2004-07-20 16:50 ` trt at acm dot org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-07-19 18:35 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-07-19 18:35 -------
Confirmed.
--
What |Removed |Added
----------------------------------------------------------------------------
Severity|minor |enhancement
Status|UNCONFIRMED |NEW
Component|c |tree-optimization
Ever Confirmed| |1
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2004-07-19 18:35:45
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/16632] A couple fold-const.c optimizations are non-functional
2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
2004-07-19 18:35 ` [Bug tree-optimization/16632] " pinskia at gcc dot gnu dot org
@ 2004-07-20 16:50 ` trt at acm dot org
2004-08-24 14:41 ` trt at acm dot org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: trt at acm dot org @ 2004-07-20 16:50 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From trt at acm dot org 2004-07-20 16:50 -------
Silly me, the demo code should have returned a value:
int subr(int i)
{
if ((i|3) == 1) return 1; /* never taken */
if ((i&4) == 2) return 1; /* never taken */
return 0;
}
This should simplify to "return 0;" but the assembler code retains the 'or'
and 'and' even at high optimization levels.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/16632] A couple fold-const.c optimizations are non-functional
2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
2004-07-19 18:35 ` [Bug tree-optimization/16632] " pinskia at gcc dot gnu dot org
2004-07-20 16:50 ` trt at acm dot org
@ 2004-08-24 14:41 ` trt at acm dot org
2004-10-03 14:43 ` pinskia at gcc dot gnu dot org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: trt at acm dot org @ 2004-08-24 14:41 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From trt at acm dot org 2004-08-24 14:41 -------
Could someone please review and apply this patch?
In my opinion, the problem and patch are quite straightforward.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/16632] A couple fold-const.c optimizations are non-functional
2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
` (2 preceding siblings ...)
2004-08-24 14:41 ` trt at acm dot org
@ 2004-10-03 14:43 ` pinskia at gcc dot gnu dot org
2004-10-03 15:33 ` cvs-commit at gcc dot gnu dot org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-10-03 14:43 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-10-03 14:43 -------
Patch here: <http://gcc.gnu.org/ml/gcc-patches/2004-10/msg00194.html>.
--
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |patch
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/16632] A couple fold-const.c optimizations are non-functional
2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
` (3 preceding siblings ...)
2004-10-03 14:43 ` pinskia at gcc dot gnu dot org
@ 2004-10-03 15:33 ` cvs-commit at gcc dot gnu dot org
2004-10-03 15:34 ` kazu at cs dot umass dot edu
2004-10-15 17:15 ` pinskia at gcc dot gnu dot org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu dot org @ 2004-10-03 15:33 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From cvs-commit at gcc dot gnu dot org 2004-10-03 15:33 -------
Subject: Bug 16632
CVSROOT: /cvs/gcc
Module name: gcc
Changes by: kazu@gcc.gnu.org 2004-10-03 15:33:21
Modified files:
gcc : ChangeLog
gcc/testsuite : ChangeLog
Log message:
PR tree-optimization/16632
* fold-const.c (fold) [EQ_EXPR]: When seeing if D & ~C != 0 to
fold (A & C) == D into 0, fold ~C. Similarly, for the case
where | is used instead of &.
PR tree-optimization/16632
* testsuite/gcc.dg/tree-ssa/20041002-1.c: New.
Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.5730&r2=2.5731
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.4374&r2=1.4375
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/16632] A couple fold-const.c optimizations are non-functional
2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
` (4 preceding siblings ...)
2004-10-03 15:33 ` cvs-commit at gcc dot gnu dot org
@ 2004-10-03 15:34 ` kazu at cs dot umass dot edu
2004-10-15 17:15 ` pinskia at gcc dot gnu dot org
6 siblings, 0 replies; 8+ messages in thread
From: kazu at cs dot umass dot edu @ 2004-10-03 15:34 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From kazu at cs dot umass dot edu 2004-10-03 15:34 -------
Just checked in the fix.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/16632] A couple fold-const.c optimizations are non-functional
2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
` (5 preceding siblings ...)
2004-10-03 15:34 ` kazu at cs dot umass dot edu
@ 2004-10-15 17:15 ` pinskia at gcc dot gnu dot org
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-10-15 17:15 UTC (permalink / raw)
To: gcc-bugs
--
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |4.0.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16632
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2004-10-15 17:15 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
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2004-07-19 18:05 [Bug c/16632] New: A couple fold-const.c optimizations are non-functional trt at acm dot org
2004-07-19 18:35 ` [Bug tree-optimization/16632] " pinskia at gcc dot gnu dot org
2004-07-20 16:50 ` trt at acm dot org
2004-08-24 14:41 ` trt at acm dot org
2004-10-03 14:43 ` pinskia at gcc dot gnu dot org
2004-10-03 15:33 ` cvs-commit at gcc dot gnu dot org
2004-10-03 15:34 ` kazu at cs dot umass dot edu
2004-10-15 17:15 ` pinskia at gcc dot gnu dot org
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