Compiling with optimization
Jens-Christian Lache
lache@tu-harburg.de
Mon Dec 4 07:04:00 GMT 2000
Hi! I still have problems with the compiler-switches.
I have written a program, which should measure how many clock-ticks
a multiply&acc. (mla) operation takes on my arm7tdmi-cpu. If I do not
use -O2, I get a big measure-overhead and three clock-ticks
for a "mla", which is the correct value. If I use optimization, I get a
small overhead, but an average of 4.5 clock-ticks:
without -O2
Breakpoint 2, main () at multiplikation.mla.mess0bis32.c:75
# mla and Timer-Ticks: 0 15
# mla and Timer-Ticks: 1 17
# mla and Timer-Ticks: 4 27
# mla and Timer-Ticks: 8 38
# mla and Timer-Ticks: 16 66
# mla and Timer-Ticks: 32 110
summe: 6
with -O2
Breakpoint 2, main () at multiplikation.mla.mess0bis32.c:77
# mla and Timer-Ticks: 0 2
# mla and Timer-Ticks: 1 6
# mla and Timer-Ticks: 4 20
# mla and Timer-Ticks: 8 38
# mla and Timer-Ticks: 16 78
# mla and Timer-Ticks: 32 146
summe: 6
I compile with:
arm-elf-gcc -mapcs-32 -mapcs-frame -mcpu=arm7tdmi -DAT91M40400 -DDEBUG\
-I/home/hiwi/lache/c/Include -O2 -o multiplikation.mla.mess0bis32.arm\
-Wl,-T/home/hiwi/lache/c/linker/linker.script.sc \
multiplikation.mla.mess0bis32.c
arm-elf-gcc -mapcs-32 -mapcs-frame -mcpu=arm7tdmi -DAT91M40400\
-DDEBUG -I/home/hiwi/lache/c/Include -S -O2
multiplikation.mla.mess0bis32.c
The funny thing is, that the assembler looks allright...
What can that be?
Jens-Christian
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