[openmp][wasm] Inform CMake of a new WebAssembly target

This change touches CMake files only. It sets up a new `LIBOMP_ARCH`
option--`wasm32`--and provides a handy `WASM` shortcut variable for
internal CMake use like other targets do. This also disables shared
library support (WebAssembly expects a static one) and the
`LIBOMPTARGET` functionality when targeting WebAssembly.

Author: abrown

openmp/CMakeLists.txt

@@ -94,7 +94,7 @@ set(ENABLE_LIBOMPTARGET ON)
 # Since the device plugins are only supported on Linux anyway,
 # there is no point in trying to compile libomptarget on other OSes.
 # 32-bit systems are not supported either.
-if (APPLE OR WIN32 OR NOT "cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES OR NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
+if (APPLE OR WIN32 OR WASM OR NOT "cxx_std_17" IN_LIST CMAKE_CXX_COMPILE_FEATURES OR NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
   set(ENABLE_LIBOMPTARGET OFF)
 endif()
 

openmp/runtime/CMakeLists.txt

@@ -30,7 +30,7 @@ if(${OPENMP_STANDALONE_BUILD})
   # If adding a new architecture, take a look at cmake/LibompGetArchitecture.cmake
   libomp_get_architecture(LIBOMP_DETECTED_ARCH)
   set(LIBOMP_ARCH ${LIBOMP_DETECTED_ARCH} CACHE STRING
-    "The architecture to build for (x86_64/i386/arm/ppc64/ppc64le/aarch64/mic/mips/mips64/riscv64/loongarch64/ve/s390x).")
+    "The architecture to build for (x86_64/i386/arm/ppc64/ppc64le/aarch64/mic/mips/mips64/riscv64/loongarch64/ve/s390x/wasm32).")
   # Should assertions be enabled?  They are on by default.
   set(LIBOMP_ENABLE_ASSERTIONS TRUE CACHE BOOL
     "enable assertions?")
@@ -67,6 +67,8 @@ else() # Part of LLVM build
     set(LIBOMP_ARCH ve)
   elseif(LIBOMP_NATIVE_ARCH MATCHES "s390x")
     set(LIBOMP_ARCH s390x)
+  elseif(LIBOMP_NATIVE_ARCH MATCHES "wasm")
+    set(LIBOMP_ARCH wasm32)
   else()
     # last ditch effort
     libomp_get_architecture(LIBOMP_ARCH)
@@ -87,7 +89,7 @@ if(LIBOMP_ARCH STREQUAL "aarch64")
   endif()
 endif()
 
-libomp_check_variable(LIBOMP_ARCH 32e x86_64 32 i386 arm ppc64 ppc64le aarch64 aarch64_a64fx mic mips mips64 riscv64 loongarch64 ve s390x)
+libomp_check_variable(LIBOMP_ARCH 32e x86_64 32 i386 arm ppc64 ppc64le aarch64 aarch64_a64fx mic mips mips64 riscv64 loongarch64 ve s390x wasm32)
 
 set(LIBOMP_LIB_TYPE normal CACHE STRING
   "Performance,Profiling,Stubs library (normal/profile/stubs)")
@@ -168,6 +170,7 @@ set(RISCV64 FALSE)
 set(LOONGARCH64 FALSE)
 set(VE FALSE)
 set(S390X FALSE)
+set(WASM FALSE)
 if("${LIBOMP_ARCH}" STREQUAL "i386" OR "${LIBOMP_ARCH}" STREQUAL "32")    # IA-32 architecture
   set(IA32 TRUE)
 elseif("${LIBOMP_ARCH}" STREQUAL "x86_64" OR "${LIBOMP_ARCH}" STREQUAL "32e") # Intel(R) 64 architecture
@@ -198,6 +201,8 @@ elseif("${LIBOMP_ARCH}" STREQUAL "ve") # VE architecture
     set(VE TRUE)
 elseif("${LIBOMP_ARCH}" STREQUAL "s390x") # S390x (Z) architecture
     set(S390X TRUE)
+elseif("${LIBOMP_ARCH}" STREQUAL "wasm32") # WebAssembly architecture
+    set(WASM TRUE)
 endif()
 
 # Set some flags based on build_type
@@ -306,6 +311,11 @@ endif()
 set(LIBOMP_ENABLE_SHARED TRUE CACHE BOOL
   "Shared library instead of static library?")
 
+if(WASM)
+  libomp_warning_say("The WebAssembly build currently only supports static libraries; forcing LIBOMP_ENABLE_SHARED to false")
+  set(LIBOMP_ENABLE_SHARED FALSE)
+endif()
+
 if(WIN32 AND NOT LIBOMP_ENABLE_SHARED)
   libomp_error_say("Static libraries requested but not available on Windows")
 endif()

openmp/runtime/cmake/LibompGetArchitecture.cmake

@@ -53,6 +53,8 @@ function(libomp_get_architecture return_arch)
       #error ARCHITECTURE=ve
     #elif defined(__s390x__)
       #error ARCHITECTURE=s390x
+    #elif defined(__wasm32__)
+      #error ARCHITECTURE=wasm32
     #else
       #error ARCHITECTURE=UnknownArchitecture
     #endif

openmp/runtime/cmake/config-ix.cmake

@@ -150,15 +150,20 @@ if(CMAKE_C_COMPILER_ID STREQUAL "Intel" OR CMAKE_C_COMPILER_ID STREQUAL "IntelLL
   check_library_exists(irc_pic _intel_fast_memcpy "" LIBOMP_HAVE_IRC_PIC_LIBRARY)
 endif()
 
-# Checking Threading requirements
-find_package(Threads REQUIRED)
-if(WIN32)
-  if(NOT CMAKE_USE_WIN32_THREADS_INIT)
-    libomp_error_say("Need Win32 thread interface on Windows.")
-  endif()
-else()
-  if(NOT CMAKE_USE_PTHREADS_INIT)
-    libomp_error_say("Need pthread interface on Unix-like systems.")
+# Checking threading requirements. Note that compiling to WebAssembly threads
+# with either the Emscripten or wasi-threads flavor ends up using the pthreads
+# interface in a WebAssembly-compiled libc; CMake does not yet know how to
+# detect this.
+if (NOT WASM)
+  find_package(Threads REQUIRED)
+  if(WIN32)
+    if(NOT CMAKE_USE_WIN32_THREADS_INIT)
+      libomp_error_say("Need Win32 thread interface on Windows.")
+    endif()
+  else()
+    if(NOT CMAKE_USE_PTHREADS_INIT)
+      libomp_error_say("Need pthread interface on Unix-like systems.")
+    endif()
   endif()
 endif()