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Editorial Team
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Asked: 2026-06-06T17:03:11+00:00

I’m doing some number crunching in C++, and I’m seeing a vast difference in

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I’m doing some number crunching in C++, and I’m seeing a vast difference in CPU % usage when using -Os optimization in my Debug build. I would therefore like to profile my code with optimizations enabled, so that I don’t waste time optimizing code that the compiler already optimizes well.

When I try to profile with -Os optimization, I can’t get Instruments to symbolicate my code (even when I manually specify the location of my .dSYM file). It won’t even show my top-level C++ member functions that are not templated or inlined.

I can get it to symbolicate fine when I specify the default -O0 optimization level.

So, is it even possible to profile with optimizations enabled? If so, then what’s the trick to make it work?

I’m using XCode 4.3.3.

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  1. Editorial Team

    Time Profiler did indeed symbolicate when using -Os. The optimizer did it’s job so well, that my C++ DSP code got inlined and speeded up to the point where the profiler would not sample any of it in the short amount of time that I let it run. All I could see in the call tree were system calls.

    When I tried running the profiler for longer, the profiler caught a few blips of my DSP code. It only showed my top-level DSP function called by some NSOperationQueue handler. The rest underneath seemed to be all inlined.

    I got more useful results when I compiled with -O2. More of my DSP subroutines were left intact (instead of being inlined), so I was better able to gauge where my DSP algorithm was spending its time. But all that is moot, because now I can see that the app is spending vastly more time in housekeeping system calls than in my DSP code.

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