[LLVMdev] Instruction Scheduling

[Fernando Magno Quintao Pereira]

Hi, guys,

     I am comparing the performance of the default scheduler (seems to be 
the one that minimizes register pressure) with no scheduler 
(-pre-RA-sched=none), and I got these numbers. The ratio is 
low_reg_pressure/none, that is, the lower the number, the better the 
performance with low register pressure:

CFP2000/177.mesa/177.mesa               1.00
CFP2000/179.art/179.art                 0.98
CFP2000/183.equake/183.equake           1.00
CFP2000/188.ammp/188.ammp               0.98
CINT2000/164.gzip/164.gzip              0.97
CINT2000/175.vpr/175.vpr                0.97
CINT2000/176.gcc/176.gcc                n/a // crashed!
CINT2000/181.mcf/181.mcf                1.02
CINT2000/186.crafty/186.crafty          1.00
CINT2000/197.parser/197.parser          1.01
CINT2000/252.eon/252.eon                n/a // never runs
CINT2000/253.perlbmk/253.perlbmk        1.05
CINT2000/254.gap/254.gap                0.97
CINT2000/255.vortex/255.vortex          1.00
CINT2000/256.bzip2/256.bzip2            0.98
CINT2000/300.twolf/300.twolf            0.92

In three cases, I got a ratio above 1 [Must mean: scheduling had a 
negative impact on performance.] I just run it once, but I was wondering 
if this could make sense, or if I am setting the tests wrongly. I am 
running the nightly test Makefile, in a x86 linux 32 bits machine.

best,

Fernando