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[Bug target/25128] New: [m68k] Suboptimal comparisons against 65536
- From: "kazu at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 27 Nov 2005 23:28:39 -0000
- Subject: [Bug target/25128] New: [m68k] Suboptimal comparisons against 65536
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
Consider:
unsigned int bar (void);
void
foo (void)
{
unsigned int a = bar ();
if (65536 > a)
bar ();
}
./cc1 -quiet -O2 -fomit-frame-pointer generates
foo:
move.l %a2,-(%sp)
lea bar,%a2
jbsr (%a2)
cmp.l #65535,%d0
jbhi .L10
jbsr (%a2)
.L10:
move.l (%sp)+,%a2
rts
Note that
cmp.l #65535,%d0
jbhi .L10
can be replaced with
swap %d0
tst.w %d0
jbne .L10
A similar trick can be applied to signed comparisons as well.
--
Summary: [m68k] Suboptimal comparisons against 65536
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: kazu at gcc dot gnu dot org
GCC target triplet: m68k-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25128