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[Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10.
- From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 1 Sep 2005 02:03:48 -0000
- Subject: [Bug middle-end/23669] New: fold does convert (-a)/10 into a/-10.
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
Another idea from LLVM.
The following two functions should be the same asm:
int f(int a)
{
return (-a)/10;
}
int f1(int a)
{
return a/-10;
}
----
We currently get on PPC:
_f:
lis r0,0x6666
neg r3,r3
ori r0,r0,26215
mulhw r0,r3,r0
srawi r3,r3,31
srawi r0,r0,2
subf r3,r3,r0
blr
_f1:
lis r0,0x6666
ori r0,r0,26215
mulhw r0,r3,r0
srawi r3,r3,31
srawi r0,r0,2
subf r3,r0,r3
blr
As you can see f1 has one less instruction which should be better.
--
Summary: fold does convert (-a)/10 into a/-10.
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P2
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: pinskia at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org
OtherBugsDependingO 19987
nThis:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23669