From e623b688ad6fd169dfd806e191eabe973f1c26d0 Mon Sep 17 00:00:00 2001
From: oakeredolu_microsoft <oakeredolu@microsoft.com>
Date: Tue, 21 Jul 2026 10:37:26 -0700
Subject: [PATCH] Add precompiled header for kernel libraries

Profiling with vcperf showed kernels/common/default.h is the most
expensive included header, parsed in every kernel translation unit and
transitively pulling in platform.h, intrinsics.h, windows.h and heavy STL
headers. Precompile it once per ISA target via target_precompile_headers.

Measured on a full clean rebuild (5 runs each, MSVC, Release):
  baseline: 1898.5s (sd 17.05)
  post PCH: 1673.5s (sd 17.45)  ->  11.85% faster

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 78e85f7d-912f-4a77-9a1c-3c4f0316d659
---
 kernels/CMakeLists.txt | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernels/CMakeLists.txt b/kernels/CMakeLists.txt
index b82780799c..317ef99e37 100644
--- a/kernels/CMakeLists.txt
+++ b/kernels/CMakeLists.txt
@@ -357,6 +357,17 @@ target_include_directories(embree PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../include>
   $<INSTALL_INTERFACE:include>)
 
+# Precompiled header: kernels/common/default.h is included by nearly every
+# kernel translation unit and transitively pulls in platform.h, intrinsics.h,
+# windows.h and heavy STL headers. Precompiling it once per (ISA) target
+# amortizes that parse cost across all TUs of the target.
+SET(EMBREE_PCH_HEADER "${CMAKE_CURRENT_SOURCE_DIR}/common/default.h")
+FOREACH(EMBREE_PCH_TARGET embree embree_sse42 embree_avx embree_avx2 embree_avx512)
+  IF (TARGET ${EMBREE_PCH_TARGET})
+    TARGET_PRECOMPILE_HEADERS(${EMBREE_PCH_TARGET} PRIVATE "${EMBREE_PCH_HEADER}")
+  ENDIF()
+ENDFOREACH()
+
 
 # libtbb is located in same install folder as libembree
 IF(WIN32)