[openmp][WebAssembly] Allow openmp to compile and run under emscripten toolchain (#95169)

* Separate wasi and emscripten as they have different constraints and
abilities
* Emscripten mimics Linux/POSIX by statically linking the musl runtime.
This allow nearly all KMP_OS_LINUX code paths to work correctly. There
are only a few places that need to be adjusted related to dynamic
linking (dl_open)
* Internally link openmp globals
* With CommonLinkage it is needed to emit them in an assembly file, now
they are defined and used within each compilation unit
* With ExternalLinkage they suffer from duplicate symbols during linking
for unnamed globals like reduction/critical
   * Interestingly this aligns with the TODO comment above this code

Author: arsnyder16

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -7211,7 +7211,7 @@ OpenMPIRBuilder::getOrCreateInternalVariable(Type *Ty, const StringRef &Name,
     // create different versions of the function for different OMP internal
     // variables.
     auto Linkage = this->M.getTargetTriple().rfind("wasm32") == 0
-                       ? GlobalValue::ExternalLinkage
+                       ? GlobalValue::InternalLinkage
                        : GlobalValue::CommonLinkage;
     auto *GV = new GlobalVariable(M, Ty, /*IsConstant=*/false, Linkage,
                                   Constant::getNullValue(Ty), Elem.first(),

openmp/runtime/src/kmp_os.h

@@ -77,7 +77,7 @@
 
 #if (KMP_OS_LINUX || KMP_OS_WINDOWS || KMP_OS_FREEBSD || KMP_OS_NETBSD ||      \
      KMP_OS_DRAGONFLY || KMP_OS_AIX) &&                                        \
-    !KMP_OS_WASI
+    !KMP_OS_WASI && !KMP_OS_EMSCRIPTEN
 #define KMP_AFFINITY_SUPPORTED 1
 #if KMP_OS_WINDOWS && KMP_ARCH_X86_64
 #define KMP_GROUP_AFFINITY 1
@@ -1293,7 +1293,7 @@ bool __kmp_atomic_compare_store_rel(std::atomic<T> *p, T expected, T desired) {
 extern void *__kmp_lookup_symbol(const char *name, bool next = false);
 #define KMP_DLSYM(name) __kmp_lookup_symbol(name)
 #define KMP_DLSYM_NEXT(name) __kmp_lookup_symbol(name, true)
-#elif KMP_OS_WASI
+#elif KMP_OS_WASI || KMP_OS_EMSCRIPTEN
 #define KMP_DLSYM(name) nullptr
 #define KMP_DLSYM_NEXT(name) nullptr
 #else

openmp/runtime/src/kmp_platform.h

@@ -25,6 +25,7 @@
 #define KMP_OS_HURD 0
 #define KMP_OS_SOLARIS 0
 #define KMP_OS_WASI 0
+#define KMP_OS_EMSCRIPTEN 0
 #define KMP_OS_UNIX 0 /* disjunction of KMP_OS_LINUX, KMP_OS_DARWIN etc. */
 
 #ifdef _WIN32
@@ -44,6 +45,11 @@
 #elif (defined __linux__)
 #undef KMP_OS_LINUX
 #define KMP_OS_LINUX 1
+#elif defined(__EMSCRIPTEN__)
+#undef KMP_OS_LINUX
+#undef KMP_OS_EMSCRIPTEN
+#define KMP_OS_LINUX 1
+#define KMP_OS_EMSCRIPTEN 1
 #else
 #endif
 
@@ -77,7 +83,7 @@
 #define KMP_OS_SOLARIS 1
 #endif
 
-#if (defined __wasi__) || (defined __EMSCRIPTEN__)
+#if (defined __wasi__)
 #undef KMP_OS_WASI
 #define KMP_OS_WASI 1
 #endif

openmp/runtime/src/z_Linux_asm.S

@@ -2452,23 +2452,3 @@ KMP_PREFIX_UNDERSCORE(__kmp_unnamed_critical_addr):
 .section .note.GNU-stack,"",@progbits
 # endif
 #endif
-
-#if KMP_ARCH_WASM
-.data
-.global .gomp_critical_user_
-.global .gomp_critical_user_.var
-.global .gomp_critical_user_.reduction.var
-.global __kmp_unnamed_critical_addr
-.gomp_critical_user_:
-.zero 4
-.size .gomp_critical_user_, 4
-.gomp_critical_user_.var:
-.zero 4
-.size .gomp_critical_user_.var, 4
-.gomp_critical_user_.reduction.var:
-.zero 4
-.size .gomp_critical_user_.reduction.var, 4
-__kmp_unnamed_critical_addr:
-    .4byte .gomp_critical_user_
-    .size __kmp_unnamed_critical_addr, 4
-#endif