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* [Bug middle-end/18029] New: a twiddleing of a
@ 2004-10-16 2:57 kazu at cs dot umass dot edu
2004-10-16 2:57 ` [Bug middle-end/18029] an xor of a single bit bitfield is inefficient kazu at cs dot umass dot edu
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: kazu at cs dot umass dot edu @ 2004-10-16 2:57 UTC (permalink / raw)
To: gcc-bugs
Consider:
struct B {
unsigned bit : 1;
};
void
plus (struct B *b)
{
b->bit = b->bit + 1;
}
void
xor (struct B *b)
{
b->bit = b->bit ^ 1;
}
./cc1 -O2 -fomit-frame-pointer -mregparm=3 generates
plus:
xorb $1, (%eax)
ret
xor:
movb (%eax), %cl
andl $1, %ecx
xorl $1, %ecx
movzbl %cl, %ecx
movl (%eax), %edx
andl $-2, %edx
orl %ecx, %edx
movl %edx, (%eax)
ret
Note that the two functions do the same thing. Obviously, we should optimize
xor just like plus.
--
Summary: a twiddleing of a
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P2
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: kazu at cs dot umass dot edu
CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029
^ permalink raw reply [flat|nested] 8+ messages in thread* [Bug middle-end/18029] an xor of a single bit bitfield is inefficient 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu @ 2004-10-16 2:57 ` kazu at cs dot umass dot edu 2004-10-16 3:05 ` pinskia at gcc dot gnu dot org ` (5 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: kazu at cs dot umass dot edu @ 2004-10-16 2:57 UTC (permalink / raw) To: gcc-bugs -- What |Removed |Added ---------------------------------------------------------------------------- Summary|a twiddleing of a |an xor of a single bit | |bitfield is inefficient http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029 ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/18029] an xor of a single bit bitfield is inefficient 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu 2004-10-16 2:57 ` [Bug middle-end/18029] an xor of a single bit bitfield is inefficient kazu at cs dot umass dot edu @ 2004-10-16 3:05 ` pinskia at gcc dot gnu dot org 2004-10-16 15:49 ` kazu at cs dot umass dot edu ` (4 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: pinskia at gcc dot gnu dot org @ 2004-10-16 3:05 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From pinskia at gcc dot gnu dot org 2004-10-16 03:05 ------- Confirmed on PPC also. (note for PPC to get about the same code we have to use the following definition for the struct: struct B { unsigned unused: 31; unsigned bit : 1; }; ). -- What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Ever Confirmed| |1 Last reconfirmed|0000-00-00 00:00:00 |2004-10-16 03:05:12 date| | Version|unknown |4.0.0 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029 ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/18029] an xor of a single bit bitfield is inefficient 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu 2004-10-16 2:57 ` [Bug middle-end/18029] an xor of a single bit bitfield is inefficient kazu at cs dot umass dot edu 2004-10-16 3:05 ` pinskia at gcc dot gnu dot org @ 2004-10-16 15:49 ` kazu at cs dot umass dot edu 2004-10-17 11:26 ` giovannibajo at libero dot it ` (3 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: kazu at cs dot umass dot edu @ 2004-10-16 15:49 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From kazu at cs dot umass dot edu 2004-10-16 15:49 ------- A patch here: http://gcc.gnu.org/ml/gcc-patches/2004-10/msg01333.html -- What |Removed |Added ---------------------------------------------------------------------------- Keywords| |patch http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029 ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/18029] an xor of a single bit bitfield is inefficient 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu ` (2 preceding siblings ...) 2004-10-16 15:49 ` kazu at cs dot umass dot edu @ 2004-10-17 11:26 ` giovannibajo at libero dot it 2005-01-13 18:57 ` pinskia at gcc dot gnu dot org ` (2 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: giovannibajo at libero dot it @ 2004-10-17 11:26 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From giovannibajo at libero dot it 2004-10-17 11:26 ------- Approved for 4.1. -- What |Removed |Added ---------------------------------------------------------------------------- OtherBugsDependingO| |17652 nThis| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029 ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/18029] an xor of a single bit bitfield is inefficient 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu ` (3 preceding siblings ...) 2004-10-17 11:26 ` giovannibajo at libero dot it @ 2005-01-13 18:57 ` pinskia at gcc dot gnu dot org 2005-03-02 16:06 ` cvs-commit at gcc dot gnu dot org 2005-03-02 16:08 ` kazu at cs dot umass dot edu 6 siblings, 0 replies; 8+ messages in thread From: pinskia at gcc dot gnu dot org @ 2005-01-13 18:57 UTC (permalink / raw) To: gcc-bugs -- What |Removed |Added ---------------------------------------------------------------------------- Target Milestone|--- |4.1.0 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029 ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/18029] an xor of a single bit bitfield is inefficient 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu ` (4 preceding siblings ...) 2005-01-13 18:57 ` pinskia at gcc dot gnu dot org @ 2005-03-02 16:06 ` cvs-commit at gcc dot gnu dot org 2005-03-02 16:08 ` kazu at cs dot umass dot edu 6 siblings, 0 replies; 8+ messages in thread From: cvs-commit at gcc dot gnu dot org @ 2005-03-02 16:06 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From cvs-commit at gcc dot gnu dot org 2005-03-02 16:05 ------- Subject: Bug 18029 CVSROOT: /cvs/gcc Module name: gcc Changes by: kazu@gcc.gnu.org 2005-03-02 16:05:00 Modified files: gcc : ChangeLog expr.c Log message: PR middle-end/18029 and PR middle-end/18030 * expr.c (optimize_bitfield_assignment_op): Add a special case to handle BIT_IOR_EXPR and BIT_XOR_EXPR. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.7632&r2=2.7633 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/expr.c.diff?cvsroot=gcc&r1=1.778&r2=1.779 -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029 ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug middle-end/18029] an xor of a single bit bitfield is inefficient 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu ` (5 preceding siblings ...) 2005-03-02 16:06 ` cvs-commit at gcc dot gnu dot org @ 2005-03-02 16:08 ` kazu at cs dot umass dot edu 6 siblings, 0 replies; 8+ messages in thread From: kazu at cs dot umass dot edu @ 2005-03-02 16:08 UTC (permalink / raw) To: gcc-bugs ------- Additional Comments From kazu at cs dot umass dot edu 2005-03-02 16:07 ------- Just checked in a patch. -- What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution| |FIXED http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18029 ^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2005-03-02 16:08 UTC | newest] Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2004-10-16 2:57 [Bug middle-end/18029] New: a twiddleing of a kazu at cs dot umass dot edu 2004-10-16 2:57 ` [Bug middle-end/18029] an xor of a single bit bitfield is inefficient kazu at cs dot umass dot edu 2004-10-16 3:05 ` pinskia at gcc dot gnu dot org 2004-10-16 15:49 ` kazu at cs dot umass dot edu 2004-10-17 11:26 ` giovannibajo at libero dot it 2005-01-13 18:57 ` pinskia at gcc dot gnu dot org 2005-03-02 16:06 ` cvs-commit at gcc dot gnu dot org 2005-03-02 16:08 ` kazu at cs dot umass dot edu
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