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

[Kristóf Umann via llvm-dev]

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I've quickly learned that its outdated, because the script it talks about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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