[lldb-dev] lldb compiled from source 5X slower than homebrew or default lldb

[Timothee Cour via lldb-dev]

after further inspection it turns out it's a performance regression
between llvm 5 and llvm 6:

$homebrew_D/Cellar/llvm/5.0.1/lldb -s test_lldb.txt -- prog
8 seconds
$homebrew_D/Cellar/llvm/6.0.0/bin/lldb -s test_lldb.txt -- prog
40 seconds

cat test_lldb.txt:
```
b FOO
r
bt
q
```

prog is some binary I'm debugging. It's unfortunately hard to reduce.
What are good ways to investigate this?



On Mon, Mar 12, 2018 at 1:42 PM, Adrian Prantl <aprantl at apple.com> wrote:
> Have you tried diff'ing your cmake invocation against the on used by homebrew?
>
> -- adrian
>
>> On Mar 9, 2018, at 12:59 AM, Timothee Cour via lldb-dev <lldb-dev at lists.llvm.org> wrote:
>>
>> while testing out https://github.com/llvm-mirror/lldb/pull/3 I noticed
>> that when I compiled lldb from source (even un-modified from git HEAD)
>> it was 5X slower than homebrew lldb or default lldb:
>>
>> I'm compiling lldb as follows:
>> ```
>> git clone https://github.com/llvm-mirror/llvm.git
>> cd llvm/tools
>> git clone https://github.com/llvm-mirror/lldb
>> ## also, patch in https://github.com/llvm-mirror/lldb/pull/3
>> git clone https://github.com/llvm-mirror/clang
>> cd ..
>> mkdir build
>> cd build
>> ccmake .. -G Ninja
>> # here I set: CMAKE_BUILD_TYPE      Release
>> ninja all
>> ```
>>
>> I also tried setting `LLVM_ENABLE_ASSERTIONS OFF` but no difference
>>
>>
>> commands.txt
>> ```
>> b FOO
>> r
>> bt
>> q
>> ```
>>
>> ./test is some program i have.
>>
>> ```
>> time lldb -s commands.txt -- ./test
>> 8 seconds
>> time ./build/bin/lldb -s commands.txt -- ./test
>> 40 seconds
>> ```
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>