GCC 4.1.1 (probably all 4.* versions, tested 4.3.0-svn also), uses cmp/eq
instead of "dt" in loops. This leads to ~20% perfomance decrease.
Technically, loop processing algorithm is completely different between
versions.
Example (sources in attach):
CFLAGS="-m4 -O3 -fomit-frame-pointer"
gcc 3.4.4:
----------------------------
.LFB2:
mov.l .L11,r3
mov #0,r0
mov.l .L12,r2
.L5:
mov.l @r3+,r1 ! !!!
dt r2 ! !!!
bf/s .L5
add r1,r0
rts
nop
.L13:
.align 2
.L11:
.long -1946157056
.L12:
.long 1000000
-----------------------------
gcc 4.1.1:
-----------------------------
.LFB2:
mov.l .L8,r2
mov #0,r0
mov.l .L9,r3
.L2:
mov.l @r2+,r1 ! !!!
cmp/eq r3,r2 ! !!!
bf/s .L2
add r1,r0
rts
nop
.L10:
.align 2
.L8:
.long -1946157056
.L9:
.long -1942157056
-----------------------------
P.S. We are porting application from gcc3.4 to gcc4.1 and have about 60%
perfomance decrease. So this is probably just first report. :(
--
Summary: [SH-4] Perfomance regression in loops. cmp/eq used
instead of dt
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: nbkolchin at gmail dot com
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: sh-rtemself
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29953
