[llvm] [openmp] [openmp][wasm] Allow openmp to compile and run under emscripten toolchain (PR #95169)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-openmp

Author: arsnyder16 (arsnyder16)

<details>
<summary>Changes</summary>

* 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

---
Full diff: https://github.com/llvm/llvm-project/pull/95169.diff


4 Files Affected:

- (modified) llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp (+1-1) 
- (modified) openmp/runtime/src/kmp_os.h (+2-2) 
- (modified) openmp/runtime/src/kmp_platform.h (+7-1) 
- (modified) openmp/runtime/src/z_Linux_asm.S (-20) 


``````````diff
diff --git a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
index 5154c33502526..01c8ae3a6e867 100644
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -5356,7 +5356,7 @@ 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(),
diff --git a/openmp/runtime/src/kmp_os.h b/openmp/runtime/src/kmp_os.h
index 24b40ed32d988..2252f5e7e97a7 100644
--- a/openmp/runtime/src/kmp_os.h
+++ b/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
diff --git a/openmp/runtime/src/kmp_platform.h b/openmp/runtime/src/kmp_platform.h
index 200fdf697dd0e..9c2215140467d 100644
--- a/openmp/runtime/src/kmp_platform.h
+++ b/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
diff --git a/openmp/runtime/src/z_Linux_asm.S b/openmp/runtime/src/z_Linux_asm.S
index 5b614e26a8337..f119f64647daa 100644
--- a/openmp/runtime/src/z_Linux_asm.S
+++ b/openmp/runtime/src/z_Linux_asm.S
@@ -2452,23 +2452,3 @@ KMP_PREFIX_UNDERSCORE(__kmp_unnamed_critical_addr):
 .section .note.GNU-stack,"", at 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

``````````

</details>


https://github.com/llvm/llvm-project/pull/95169