================
@@ -26,9 +30,23 @@ if(LLVM_BUILD_INSTRUMENTED)
message(STATUS "To enable merging PGO data LLVM_PROFDATA has to point to
llvm-profdata")
else()
add_custom_target(generate-profdata
- COMMAND "${Python3_EXECUTABLE}"
${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py merge ${LLVM_PROFDATA}
${CMAKE_CURRENT_BINARY_DIR}/clang.profdata ${CMAKE_CURRENT_BINARY_DIR}
+ COMMAND "${Python3_EXECUTABLE}"
${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py merge ${LLVM_PROFDATA}
${CMAKE_CURRENT_BINARY_DIR}/clang.profdata ${CMAKE_CURRENT_BINARY_DIR}
${CMAKE_BINARY_DIR}/profiles/
COMMENT "Merging profdata"
DEPENDS generate-profraw)
+ if (CLANG_PGO_TRAINING_DATA_SOURCE_DIR)
+ llvm_ExternalProject_Add(generate-profraw-external
${CLANG_PGO_TRAINING_DATA_SOURCE_DIR}
+ USE_TOOLCHAIN EXLUDE_FROM_ALL NO_INSTALL DEPENDS
generate-profraw)
+ add_dependencies(generate-profdata generate-profraw-external)
+ else()
+ # Default to compiling a file from clang. This also builds all the
+ # dependencies needed to build this file, like TableGen.
+ set(generate_profraw_clang_sema
tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/Sema.cpp.o)
+ llvm_ExternalProject_Add(generate-profraw-clang
${CMAKE_CURRENT_SOURCE_DIR}/../../../llvm
+ USE_TOOLCHAIN EXLUDE_FROM_ALL NO_INSTALL DEPENDS generate-profraw
+ EXTRA_TARGETS generate_profraw_clang_sema
----------------
tstellar wrote:
> This is going to be really fragile. The paths of object file outputs are an
> implementation detail of CMake that has changed in the past and could change
> in the future, also I think only the makefile and ninja generator actually
> export those as buildable targets.
>
What about using the library target `clangSema` instead of the individual file?
> Beyond that I also have a philosophical problem with the approach of using
> living clang sources as training data. I think this can result in
> unexplainable or difficult to diagnose differences in the efficacy of PGO
> because as you change the compiler you're also innately changing the training
> data. A potential better solution would be to have a preprocessed Sema.cpp
> from a recent LLVM release that we check in as a stable copy. This would be
> similar to how the GCC compile-time benchmark works.
The first thing I tried to do was add a preprocessed version of
CommentSema.cpp, but the file was 10MB, and I thought that might be too big.
Sema.cpp preprocessed is 5MB, which is smaller but still pretty big. I would
be OK with this approach if we think it's OK to add a big file like this to the
repo.
I'm also not concerned about efficacy of PGO, because building Sema.cpp is just
the default. I really want there to be a good default experience for users, so
that they can use the PGO cache files and things will 'just work'. This patch
also adds a configuration option for advanced users that need something more
consistent.
https://github.com/llvm/llvm-project/pull/77347
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