[llvm-dev] Struggling with a PGO build of clang -- llvm-profdata was built without zlib support?

[David Blaikie via llvm-dev]

I /guess/ you actually want /path/to/release_build/llvm-profdata because
the profiles are generated from binaries compiled with the release build,
so it's the release build that matters for all things profiling related, I
would think, in your situation.


On Tue, Sep 3, 2019 at 10:06 AM Kristóf Umann via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi!
>
> I'm trying to build a fast Clang for myself to use for debug builds on
> Clang itself, but I've been struggling for a very long time on it. Could
> you please help?
>
> I've been following this guide:
> https://llvm.org/docs/HowToBuildWithPGO.html
>
> I've quickly learned that its outdated, because the script it talks about
> doesn't work with the monorepo layout at all, but in any case, it does
> describe how to do the entire process by hand, so I went for that. Here are
> my steps:
>
> * Built a release version of LLVM/Clang/LLD/compiler-rt on version
> 9.0.0-rc3
>
> * Built an instrumented clang with the following config:
> cmake -G Ninja ../llvm \
>   -DLLVM_ENABLE_PROJECTS='clang;compiler-rt' \
>   -DLLVM_TARGETS_TO_BUILD=X86 \
>   -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
>   -DCMAKE_CXX_COMPILER=/path/to/release_build/bin/clang++ \
>   -DCMAKE_C_COMPILER=/path/to/release_build/bin/clang \
>   -DLLVM_USE_LINKER=/path/to/release_build/bin/ld.lld \
>   -DLLVM_CCACHE_BUILD=ON \
>   -DLLVM_BUILD_INSTRUMENTED=IR \
>   -DLLVM_BUILD_RUNTIME=No \
>   -DLLVM_ENABLE_ZLIB=1 \
>   -DCMAKE_BUILD_TYPE=Release \
>   -DLLVM_ENABLE_LTO=Thin \
>   -DCMAKE_RANLIB=/path/to/release_build/bin/llvm-ranlib \
>   -DCMAKE_AR=/path/to/release_build/bin/llvm-ar
>
> I tried this without specifying zlib being enabled, without thinlto,
> everything I could come up with really.
>
> * Built a debug Clang with the following configuration:
> cmake -G Ninja ../llvm \
>   -DCMAKE_BUILD_TYPE=Debug \
>   -DLLVM_ENABLE_PROJECTS='clang' \
>   -DBUILD_SHARED_LIBS=ON \
>   -DLLVM_TARGETS_TO_BUILD=X86 \
>   -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
>   -DCMAKE_CXX_COMPILER=/path/to/instrumented_build/bin/clang++ \
>   -DCMAKE_C_COMPILER=/path/to/instrumented_build/bin/clang \
>   -DLLVM_USE_LINKER=/path/to/release_build/bin/ld.lld  \
>   -DLLVM_CCACHE_BUILD=ON
>
> * Tried to use /path/to/instrumented_build/llvm-profdata on the profraw
> files found in  /path/to/instrumented_build/profiles/.
>
> I got the following error message:
> error: profiles/default_15822678447050577402_0.profraw: Profile uses zlib
> compression but the profile reader was built without zlib support
>
> Even when I explicitly specified zlib to be enabled, and double check
> whether zlib.h was found I got this message. I've found this [1] thread
> mentioning a similar issue, but I'm unfortunately not familiar enough with
> LLVM itself to use the discussed tips with any success. Is there something
> obvious I'm missing?
>
> Thanks in advance,
> Kristóf
>
> [1] http://lists.llvm.org/pipermail/llvm-dev/2017-July/115588.html
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