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

[Pavel Labath via lldb-dev]

I would start by looking at https://reviews.llvm.org/D32598, which adds a
bunch of work we do up-front. I remember looking at this a while back and
not being sure whether all of that work is relevant for osx, actually. (I'm
specifically thinking of the SymbolFileDWARF::Index call, which is done
unconditionally, but I think that index is unused if we have accelerator
tables).

On Mon, 12 Mar 2018 at 21:59, Adrian Prantl via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> If this is a Mac I would recommend to build both lldbs in RelWithDebInfo
> mode and then run them through Instruments and compare the traces. I'd be
> very interested in learning what the cause for the slowdown is.
>
> -- adrian
>
> > On Mar 12, 2018, at 2:57 PM, Timothee Cour <timothee.cour2 at gmail.com>
> wrote:
> >
> > 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
> >>> ```
> >>> _______________________________________________
> >>> lldb-dev mailing list
> >>> lldb-dev at lists.llvm.org
> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
> >>
>
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