[WebAssembly] Use single-threaded mode when -matomics isn't enabled.

When the -matomics feature is not enabled, disable POSIXThreads
mode and set the thread model to Single, so that we don't predefine
macros like `__STDCPP_THREADS__`.

Differential Revision: https://reviews.llvm.org/D96091

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/lib/Basic/Targets/WebAssembly.cpp b/clang/lib/Basic/Targets/WebAssembly.cpp
index dcb3d8fd..89babe8 100644
--- a/clang/lib/Basic/Targets/WebAssembly.cpp
+++ b/clang/lib/Basic/Targets/WebAssembly.cpp
@@ -253,6 +253,15 @@ ArrayRef<Builtin::Info> WebAssemblyTargetInfo::getTargetBuiltins() const {
                                              Builtin::FirstTSBuiltin);
 }
 
+void WebAssemblyTargetInfo::adjust(LangOptions &Opts) {
+  // If the Atomics feature isn't available, turn off POSIXThreads and
+  // ThreadModel, so that we don't predefine _REENTRANT or __STDCPP_THREADS__.
+  if (!HasAtomics) {
+    Opts.POSIXThreads = false;
+    Opts.setThreadModel(LangOptions::ThreadModelKind::Single);
+  }
+}
+
 void WebAssembly32TargetInfo::getTargetDefines(const LangOptions &Opts,
                                                MacroBuilder &Builder) const {
   WebAssemblyTargetInfo::getTargetDefines(Opts, Builder);