From fb223fceeb81f481316694560ceacc473ad04b4a Mon Sep 17 00:00:00 2001
From: natsukium <tomoya.otabi@gmail.com>
Date: Thu, 23 Apr 2026 16:46:54 +0900
Subject: [PATCH] cmake: allow overriding hardcoded libomp path on macOS

The OpenMP workaround hardcoded /opt/homebrew/opt/libomp, which locked
out a custom build.
Introduce LIBOMP_ROOT (defaulting to Homebrew) so the prefix can be
overridden on the cmake command line.

While here, restrict the block to AppleClang. The flags inside are
AppleClang-specific (-Xpreprocessor -fopenmp, linking against the LLVM
libomp runtime) and were previously forced on any compiler targeting
Apple Silicon, silently breaking GCC and mis-configuring Homebrew LLVM
Clang builds.
---
 CMakeLists.txt | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5a7d3f0..d76453d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -75,15 +75,15 @@ set(KALIGN_KMEANS_UPGMA_THRESHOLD "50" CACHE STRING "Number of sequences thresho
 
 
 if(USE_OPENMP)
-  # Configure OpenMP for macOS with Homebrew (only for arm64 native builds)
-  if(APPLE AND CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "arm64" AND NOT CMAKE_OSX_ARCHITECTURES MATCHES "x86_64")
-    list(APPEND CMAKE_PREFIX_PATH /opt/homebrew)
-    # Set OpenMP flags for Apple Clang + Homebrew libomp
-    set(OpenMP_C_FLAGS "-Xpreprocessor -fopenmp -I/opt/homebrew/opt/libomp/include")
+  # Configure OpenMP for macOS with external libomp (only for Apple Clang on arm64 native builds)
+  if(APPLE AND CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "arm64" AND NOT CMAKE_OSX_ARCHITECTURES MATCHES "x86_64" AND CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
+    # Defaults to Homebrew
+    set(LIBOMP_ROOT "/opt/homebrew/opt/libomp" CACHE PATH "libomp install prefix")
+    set(OpenMP_C_FLAGS "-Xpreprocessor -fopenmp -I${LIBOMP_ROOT}/include")
     set(OpenMP_C_LIB_NAMES "omp")
-    set(OpenMP_CXX_FLAGS "-Xpreprocessor -fopenmp -I/opt/homebrew/opt/libomp/include")
+    set(OpenMP_CXX_FLAGS "-Xpreprocessor -fopenmp -I${LIBOMP_ROOT}/include")
     set(OpenMP_CXX_LIB_NAMES "omp")
-    set(OpenMP_omp_LIBRARY /opt/homebrew/opt/libomp/lib/libomp.dylib)
+    set(OpenMP_omp_LIBRARY "${LIBOMP_ROOT}/lib/libomp.dylib")
   endif()
 
   find_package(OpenMP)
