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* [Bug regression/21198] New: Packed bitfield structure copies are very inefficient
@ 2005-04-24 23:14 matt at 3am-software dot com
2005-04-25 1:09 ` [Bug regression/21198] " pinskia at gcc dot gnu dot org
0 siblings, 1 reply; 2+ messages in thread
From: matt at 3am-software dot com @ 2005-04-24 23:14 UTC (permalink / raw)
To: gcc-bugs
In a digression from 2.95, gcc 4.1 copies a packed bitfield structure member by member instead of
doing as an aggregate.
Given the program:
struct __attribute__((packed)) A { unsigned short i : 1, l : 1, j : 3, k : 11; };
struct A sA;
struct A retmeA (struct A x) { return x; }
GCC 4.1 -O3 compiles that as:
.align 1
.globl retmeA
.type retmeA, @function
retmeA:
.word 0x0
subl2 $4,%sp
movl %r1,%r0
movw 4(%ap),%r2
rotl $30,%r2,%r3
bicl2 $-8,%r3
rotl $31,%r2,%r4
bicl2 $-2,%r4
rotl $27,%r2,%r1
bicl2 $-2048,%r1
insv %r1,$5,$11,(%r0)
insv %r3,$2,$3,(%r0)
insv %r4,$1,$1,(%r0)
insv %r2,$0,$1,(%r0)
ret
.size retmeA, .-retmeA
Whereas GCC 2.95.3 compiled it to:
.globl retmeA
.type retmeA,@function
retmeA:
.word 0x0
movw 4(%ap),(%r1)
ret
--
Summary: Packed bitfield structure copies are very inefficient
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: regression
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: matt at 3am-software dot com
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: x86_64--netbsd
GCC host triplet: x86_64--netbsd
GCC target triplet: vax--netbsdelf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21198
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug regression/21198] Packed bitfield structure copies are very inefficient
2005-04-24 23:14 [Bug regression/21198] New: Packed bitfield structure copies are very inefficient matt at 3am-software dot com
@ 2005-04-25 1:09 ` pinskia at gcc dot gnu dot org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-04-25 1:09 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-04-25 01:09 -------
This is a problem with NRV.
*** This bug has been marked as a duplicate of 15596 ***
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |DUPLICATE
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21198
^ permalink raw reply [flat|nested] 2+ messages in thread
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2005-04-24 23:14 [Bug regression/21198] New: Packed bitfield structure copies are very inefficient matt at 3am-software dot com
2005-04-25 1:09 ` [Bug regression/21198] " pinskia at gcc dot gnu dot org
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