[llvm-branch-commits] [clang] release/21.x: [Clang][CMake] Use IRPGO instead of FE PGO for Cmake Caches (#155957) (PR #156271)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/156271

Backport 7fca1f841b4c226d50ab7bad64de5db225d4193b

Requested by: @boomanaiden154

>From 08383fb44eba580749dc2254effc5b1b1f96f4c4 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman at google.com>
Date: Fri, 29 Aug 2025 10:06:26 -0700
Subject: [PATCH] [Clang][CMake] Use IRPGO instead of FE PGO for Cmake Caches
 (#155957)

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 7fca1f841b4c226d50ab7bad64de5db225d4193b)
---
 clang/cmake/caches/PGO.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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