On Wednesday 23 January 2008 12:35, you wrote:
[...]
> Why "unit at a time" compilation produced faster result ? But the code
> was totally inlined and perhaps it optimised out something that it
> should not have for this purpose.
This Whetstone Benchmark is not a good test. It is
subjected to compiler optimization. Originaly with
avr-gcc 4.1.2 the result was: ~2500 bytes of flash
and ~30000 cycles. The reason was that compiler
removes tests with math function: this functions are
declared as 'const' and result is not used in external
world.
To avoid this omition I have add the calls of dummy
external functions, so all operations are present.
The 4.1.2 version is the best in both: size and speed:
> >> 4030 88565 4.1.2 -Os
> >> 5332 71751 4.1.2 -O3
But with avr-gcc 4.3-20080104 the result of '-O3' was
strange: normal size, but too quick:
5494 31547 4.3 -O3
I do not study a reason. Possibly, it was any precalculation.
I have try '-fno-unit-at-a-time' to avoid this optimization.
After this:
5608 75351
Avr-libc was the same for all versions: CVS HEAD 2008-01-13.
Regards,
Dmitry.
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