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* [Bug c/50136] New: Loop inc/dec optimization.
@ 2011-08-20 7:49 bratsinot at gmail dot com
2011-08-21 9:20 ` [Bug c/50136] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: bratsinot at gmail dot com @ 2011-08-20 7:49 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50136
Bug #: 50136
Summary: Loop inc/dec optimization.
Classification: Unclassified
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: bratsinot@gmail.com
Maybe shoud use inc and dec, than sub $1, %ebx?
GCC translate this C code:
unsigned int i;
scanf("%u", &i);
for(unsigned int qwe=i; qwe>0; qwe--)
printf("fg");
Into this Assembler code:
leaq 12(%rsp), %rsi
xorl %eax, %eax
movl $.LC0, %edi
call __isoc99_scanf
movl 12(%rsp), %ebx
testl %ebx, %ebx
je .L2
.p2align 4,,10
.p2align 3
.L4:
xorl %eax, %eax
movl $.LC1, %edi
call printf
subl $1, %ebx ;This not good, dec %ebx is better
jne .L4
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug c/50136] Loop inc/dec optimization.
2011-08-20 7:49 [Bug c/50136] New: Loop inc/dec optimization bratsinot at gmail dot com
@ 2011-08-21 9:20 ` rguenth at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2011-08-21 9:20 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50136
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |WORKSFORME
--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-08-21 09:20:05 UTC ---
inc/dec is chosen if you compile for selected CPUs where this is the
faster variant.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2011-08-20 7:49 [Bug c/50136] New: Loop inc/dec optimization bratsinot at gmail dot com
2011-08-21 9:20 ` [Bug c/50136] " rguenth at gcc dot gnu.org
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