[PATCH] splits after reload

["Rakesh Kumar - Software, Noida" <rakeshku at noida dot hcltech dot com>]

Hi,

The problem has been previously discussed under
following threads

http://gcc.gnu.org/ml/gcc/2003-12/msg00700.html

http://gcc.gnu.org/ml/gcc/2004-01/msg00042.html

After little thought and some experimentation,
I realized that peephole2 is not the solution to
this problem. Peepholes work on the patterns of
insns and hence the insn chain can't be
traversed for recombinations.
At the same time, I agree that recording insns
at the time of split and hacking
peephole is fragile.

I'd like to advocate defining the target hook for
recombining splits in split_all_insns (). If an INSN
is split, the target hook is called with
PREV_INSN (INSN) and the last insn generated
in split as arguments. The target can check for
each insn in split sequence as possible candidate
for recombination. The default value for the
target hook is 0, so it would not burden the
targets which do not override it. Certainly,
it might help the targets which got interested
towards recombining splits.

I implemented the hook on SH4 target. I'm
combining only ADD insns, since that is
requirement for SH. There are a hoard of other
operations possible.

The attached patch is fully tested with GCC
testsuite and stress-1.17. I'm getting the
following size gains with -O2 -ml -m4 switches.

Stress		Mainline	With Split		%age
Testcase		GCC		Recombination	Gain
--------		--------	-------------	-----
ls_step.i		3968		3744			5.64
gentest.c		1184		1120			5.4
decode.i		1380		1316			4.63
dct64.i		1792		1728			3.57
navion_gear.i	1912		1848			3.35
ls_accel.i		3232		3136			2.97
scanline.i		2304		2240			2.77
vorbis_mdct.i	2688		2624			2.38
layer3.i		19952		19568			1.92
clip.i		14012		13788			1.6
tonal.i		10928		10768			1.46
layer2.i		2400		2368			1.33
g_misc.i		22140		21852			1.3
slalom.i		9376		9280			1.02

Other test cases showing below 1% improvement are:
attstub.i, avl.i, compress.i, gems.i, g_func.i,
imdecode.i, index.c, l3psy.i, linpackc.i, lndsub.i,
ls_aux.i, mathutil.i, player.i, quantize.i, rengine.i,
revolt.i, segment.i, shear.i, slib.i, smallft.i,
sound.i, xvalg.i

Please review the attached patch and let me know your
valuable comments. I'd be thankful.

Regards and Thanks,
Rakesh Kumar

Attachment: ChangeLog
Description: Binary data

Attachment: patch_recombine
Description: Binary data