Compiler optimization level having no effect

Evan Haas

I have some benchmark programs that I have been working with for a while. I have found in the past (not surprisingly) that there is a drastic improvement on performance times when going from no optimization to -2 or -3. However, for the past 2 days I've found that my compiler optimization level has no impact. Regardless of the setting it's as if optimization is off. I had been using CCS5, so I tried switching back to CCS4 but it behaved the same. I then made a new project and imported the source code to build from a new project, but it still behaved the same. In the console it shows "C:/TI/ccsv4/tools/compiler/c6000/bin/cl6x" -mv64+ -g -O2 " So it looks like the compiler setting is being passed down correctly. Can anyone explain this behavior?

over 14 years ago

Archaeologist over 14 years ago

TI__Guru* 84285 points

Using "-g" can greatly inhibit optimization. In your past comparisons, were you using "-g"?

Evan Haas over 14 years ago in reply to Archaeologist

Intellectual 435 points

I'm pretty sure I was always using that. But what you would recommend changing it to?

Archaeologist over 14 years ago in reply to Evan Haas

TI__Guru* 84285 points

For best optimization results, omit "-g" entirely. C6000 is particularly sensitive to this option.

As to why you are not seeing any performance delta, I can't say without looking at the compiler's assembly output files (use --keep_asm). You should be able to find a compiler-generated comment at the top of the assembly output file which tells you whether or not the file was compiled with optimization. Could you verify that you are getting optimization when you think you are, and vice versa?

Evan Haas over 14 years ago in reply to Archaeologist

Intellectual 435 points

I turned off -g and also confirmed by looking that the compiler optimization level I'm using is actually being used, by checking the assembly files. Any other thoughts as to the cause?

Archaeologist over 14 years ago in reply to Evan Haas

TI__Guru* 84285 points

There are too many things that could possibly have happened to guess. I probably can't analyze this further without a test case.

Something changed between the past and present to precipitate this delta. Did you change the compiler version? Did you change the compiler options? Did you make a change to the source code? Did you change a library version?

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Compiler optimization level having no effect