[cfe-dev] clang-tidy slow without --

[Manuel Klimek via cfe-dev]

On Sat, Jan 23, 2016 at 5:06 AM Hongping Lim via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Actually it seems "--" without anything after just means to not have any
> compile options at all?
>
> I went through the options in my compile_command.json file, and it seems
> this isysroot option is what is causing the command to be slow for this
> particular source file. If I remove it then the command runs quickly.
>
> -isysroot
> /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS9.2.sdk
>
> However, with the same compile options including the above isysroot
> option, running on another source file that I have which is 2200 lines, and
> causes 735 warnings in non-user code as well, clang-tidy takes less than
> one second.
>

1. If you don't have the right isysroot, you probably get actual compiler
errors, and clang-tidy checks will not run
2. It might be that the transitive closure of includes is just very large
when the TU takes long to process, but that'd need some more detailed
benchmarking


>
> Thanks,
> Hongping
>
>
> On Fri, Jan 22, 2016 at 7:42 PM, Hongping Lim <hongping.lim at gmail.com>
> wrote:
>
>> I have managed to build a release version of clang-tidy on my Mac, and
>> checked that it is optimized with --version.
>>
>> ~/llvm-build/bin/clang-tidy --version
>> LLVM (http://llvm.org/):
>> LLVM version 3.8.0svn
>> Optimized build.
>> Built Jan 15 2016 (13:18:26).
>> Default target: x86_64-apple-darwin15.0.0
>> Host CPU: broadwell
>>
>>
>> I am working with an Objective-C project in Xcode, and have managed to
>> generate the required compile_commands.json file using xcodebuild/xcpretty,
>> and am able to run it.
>>
>> When I run it on a single file that has 2700 lines with just the
>> compile_commands.json file (stripped down to just one command), it takes
>> clang-tidy around 23 seconds to complete.
>>
>> ~/llvm-build/bin/clang-tidy MyFile.m
>> ...
>> Suppressed 719 warnings (719 in non-user code).
>> Use -header-filter=.* to display errors from all non-system headers.
>>
>> If I run the same command with "--", then it is much faster.
>> ~/llvm-build/bin/clang-tidy MyFile.m --
>> ...
>> Suppressed 6 warnings (6 in non-user code).
>> Use -header-filter=.* to display errors from all non-system headers.
>>
>>
>>
>> It seems the difference is that with --, some header files aren't
>> processed? If I am just interested in errors in the specific file I am
>> running on, is using -- the right thing to do?
>>
>> Thanks,
>> Hongping
>>
>>
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