From d5ab3581fe655f418b3c5ad95d9a8874a9972553 Mon Sep 17 00:00:00 2001
From: Renato Golin <rengolin@systemcall.eu>
Date: Thu, 21 Nov 2024 10:28:41 +0000
Subject: [PATCH] [CMake] Add hack to find LLVM's OpenMP with GCC

---
 cmake/modules/openmp.cmake | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/cmake/modules/openmp.cmake b/cmake/modules/openmp.cmake
index 2cb2cfe3f..87fc327c4 100644
--- a/cmake/modules/openmp.cmake
+++ b/cmake/modules/openmp.cmake
@@ -1,5 +1,19 @@
 option(USE_OpenMP "Use OpenMP" ON)
 
+# We don't want GOMP because its performance sinks for large core count, so we force libomp
+# This finds the library path from the system's clang for OpenMP
+#
+# On Fedora, it's at the same place as others, so we don't need to look elsewhere
+# On Ubuntu, it's in /usr/lib/llvm-${version}, so find_package finds GOMP for GCC instead.
+execute_process (
+    COMMAND bash -c "for lib in $(clang -lomp -### 2>&1); do echo $lib | grep -o \"\\/.*llvm.*\\w\"; done"
+    OUTPUT_VARIABLE LLVM_OMP_PATH
+)
+# Only if we found an "llvm" path that we need to add
+if (LLVM_OMP_PATH)
+  set(CMAKE_PREFIX_PATH ${LLVM_OMP_PATH})
+endif()
+
 if(USE_OpenMP)
   find_package(OpenMP)
   if(OPENMP_FOUND)