[llvm-dev] My experience using -DLLVM_BUILD_INSTRUMENTED_COVERAGE to generate coverage

[Friedman, Eli via llvm-dev]

On 6/19/2017 7:29 PM, Vedant Kumar wrote:
>
>>> We can reduce testing time by *not* instrumented basic tools like 
>>> count, not, FileCheck etc. I filed: llvm.org/PR33501 
>>> <http://llvm.org/PR33501>.
>>>
>>>> 3. The generated profile information takes up a lot of space: llc 
>>>> generates a 90MB profraw file.
>>>
>>> I don't have any ideas about how to fix this. You can decrease the 
>>> space overhead for raw profiles by altering 
>>> LLVM_PROFILE_MERGE_POOL_SIZE from 4 to a lower value.
>>
>> Disk space is cheap, but the I/O takes a long time.  I guess it's 
>> specifically bad for LLVM's "make check", maybe not so bad for other 
>> cases.
>
> You can speed up "make check" a bit by using non-instrumented versions 
> of count, not, FileCheck, etc.

I tried looking into this a bit more.  It looks like the profile data 
file generated by llc contains approximately 5MB of counters 
(__llvm_prf_cnts), 10MB of "data" (__llvm_prf_data), and 70MB of 
__llvm_prf_names.  __llvm_prf_data and __llvm_prf_names contain which 
can be read from the original binary, as far as I can tell. The 80MB of 
data wouldn't be a big deal if it were just sitting on disk... but we 
also erase the whole file and rewrite it from scratch after we merge 
profile counters.

Can we do better here?

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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