Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -8137,7 +8137,8 @@
   explicit WebAssembly32TargetInfo(const llvm::Triple &T,
                                    const TargetOptions &Opts)
       : WebAssemblyTargetInfo(T, Opts) {
-    MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 32;
+    // WebAssembly MVP has no way to express atomics, so always inline them
+    MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
     resetDataLayout("e-m:e-p:32:32-i64:64-n32:64-S128");
   }
 
Index: test/Preprocessor/init.c
===================================================================
--- test/Preprocessor/init.c
+++ test/Preprocessor/init.c
@@ -8610,7 +8610,7 @@
 // WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_CHAR32_T_LOCK_FREE 2
 // WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_CHAR_LOCK_FREE 2
 // WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_INT_LOCK_FREE 2
-// WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_LLONG_LOCK_FREE 1
+// WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_LLONG_LOCK_FREE 2
 // WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_LONG_LOCK_FREE 2
 // WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_POINTER_LOCK_FREE 2
 // WEBASSEMBLY32-NEXT:#define __GCC_ATOMIC_SHORT_LOCK_FREE 2