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[Bug middle-end/23664] New: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0
- 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 00:40:15 -0000
- Subject: [Bug middle-end/23664] New: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff (C1 & C2) == 0
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
These two functions should produce the same asm:
int f(int a, int b)
{
return (a&0xF)+(b&0xF0);
}
int f1(int a, int b)
{
return (a&0xF)|(b&0xF0);
}
For PPC, we get:
_f:
rlwinm r4,r4,0,24,27
rlwinm r3,r3,0,28,31
add r3,r3,r4
blr
_f1:
rlwinm r4,r4,0,24,27
rlwimi r3,r4,0,0,27
blr
Which shows the | is more efficient than the + one.
--
Summary: fold does not change (a&C1)+(b&C2) to (a&C1)|(b&C2) iff
(C1 & C2) == 0
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
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
GCC target triplet: powerpc-*-*
OtherBugsDependingO 19987
nThis:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23664