release/21.x: [Clang][CMake] Use IRPGO instead of FE PGO for Cmake Caches (#155957) #156271
Conversation
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@mtrofin What do you think about merging this PR to the release branch? |
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@llvm/pr-subscribers-clang Author: None (llvmbot) ChangesBackport 7fca1f8 Requested by: @boomanaiden154 Full diff: https://github.com/llvm/llvm-project/pull/156271.diff 1 Files Affected:
diff --git a/clang/cmake/caches/PGO.cmake b/clang/cmake/caches/PGO.cmake
index 15bc755d110d1..d6471160037c1 100644
--- a/clang/cmake/caches/PGO.cmake
+++ b/clang/cmake/caches/PGO.cmake
@@ -5,7 +5,7 @@ set(LLVM_ENABLE_PROJECTS "clang;lld" CACHE STRING "")
set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
-set(BOOTSTRAP_LLVM_BUILD_INSTRUMENTED ON CACHE BOOL "")
+set(BOOTSTRAP_LLVM_BUILD_INSTRUMENTED IR CACHE BOOL "")
set(CLANG_BOOTSTRAP_TARGETS
generate-profdata
stage2
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This makes it easier to use the new options in the CI container since we build from the release branch. This should be a relatively safe backport given how small the change is in addition to how infrequently these CMake caches change at this point. |
Yeah. That's @tru currently. They're the only ones with merge permissions, so have to be involved either way,. |
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LGTM |
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@boomanaiden154 (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR. |
) Currently the clang CMake caches use FE PGO for instrumentation (LLVM_BUILD_INSTRUMENTED=ON). However, IRPGO is generally regarded as better for performance. I am measuring about a 1.5% performance gain when building libLLVMSupport.a using this configuration versus what existed before this commit. I would suspect the gains are larger on other platforms like Windows where we cannot subsume any gains using PLO. (cherry picked from commit 7fca1f8)
Backport 7fca1f8
Requested by: @boomanaiden154