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* [Bug middle-end/18038] New: addition in a multibit bitfield is inefficient
@ 2004-10-17 5:06 kazu at cs dot umass dot edu
2004-10-17 16:58 ` [Bug middle-end/18038] " pinskia at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: kazu at cs dot umass dot edu @ 2004-10-17 5:06 UTC (permalink / raw)
To: gcc-bugs
Consider:
struct B {
unsigned b : 2;
};
void
store (struct B *b, int v)
{
b->b += v;
}
./cc1 -O2 -fomit-frame-pointer -mregparm=3 generates
store:
movb (%eax), %cl
andl $3, %ecx
addl %edx, %ecx
andl $3, %ecx
movl (%eax), %edx
andl $-4, %edx
orl %ecx, %edx
movl %edx, (%eax)
ret
We don't need two "andl". We could do something like
store:
movl (%eax), %ecx
addl %ecx, %edx
andl $3, %edx
andl $-4, %ecx
orl %ecx, %edx
movl %edx, (%eax)
ret
--
Summary: addition in a multibit bitfield is inefficient
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=18038
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug middle-end/18038] addition in a multibit bitfield is inefficient
2004-10-17 5:06 [Bug middle-end/18038] New: addition in a multibit bitfield is inefficient kazu at cs dot umass dot edu
@ 2004-10-17 16:58 ` pinskia at gcc dot gnu dot org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-10-17 16:58 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-10-17 16:58 -------
Again for PPC:
struct B {
unsigned :30;
unsigned b : 2;
};
Confirmed.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed| |1
Last reconfirmed|0000-00-00 00:00:00 |2004-10-17 16:58:18
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18038
^ permalink raw reply [flat|nested] 2+ messages in thread
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2004-10-17 5:06 [Bug middle-end/18038] New: addition in a multibit bitfield is inefficient kazu at cs dot umass dot edu
2004-10-17 16:58 ` [Bug middle-end/18038] " pinskia at gcc dot gnu dot org
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