[clang] [Clang][CMake] Use IRPGO instead of FE PGO for Cmake Caches (PR #155957)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Aiden Grossman (boomanaiden154)

<details>
<summary>Changes</summary>

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/155957.diff


1 Files Affected:

- (modified) clang/cmake/caches/PGO.cmake (+1-1) 


``````````diff
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

``````````

</details>


https://github.com/llvm/llvm-project/pull/155957