Index: cfe/trunk/include/clang/Driver/Options.td
===================================================================
--- cfe/trunk/include/clang/Driver/Options.td
+++ cfe/trunk/include/clang/Driver/Options.td
@@ -2160,6 +2160,8 @@
 def mno_exception_handing : Flag<["-"], "mno-exception-handling">, Group<m_wasm_Features_Group>;
 def mbulk_memory : Flag<["-"], "mbulk-memory">, Group<m_wasm_Features_Group>;
 def mno_bulk_memory : Flag<["-"], "mno-bulk-memory">, Group<m_wasm_Features_Group>;
+def matomics : Flag<["-"], "matomics">, Group<m_wasm_Features_Group>;
+def mno_atomics : Flag<["-"], "mno-atomics">, Group<m_wasm_Features_Group>;
 
 def mamdgpu_debugger_abi : Joined<["-"], "mamdgpu-debugger-abi=">,
   Flags<[HelpHidden]>,
Index: cfe/trunk/lib/Basic/Targets/WebAssembly.h
===================================================================
--- cfe/trunk/lib/Basic/Targets/WebAssembly.h
+++ cfe/trunk/lib/Basic/Targets/WebAssembly.h
@@ -34,6 +34,7 @@
   bool HasSignExt = false;
   bool HasExceptionHandling = false;
   bool HasBulkMemory = false;
+  bool HasAtomics = false;
 
 public:
   explicit WebAssemblyTargetInfo(const llvm::Triple &T, const TargetOptions &)
Index: cfe/trunk/lib/Basic/Targets/WebAssembly.cpp
===================================================================
--- cfe/trunk/lib/Basic/Targets/WebAssembly.cpp
+++ cfe/trunk/lib/Basic/Targets/WebAssembly.cpp
@@ -41,6 +41,7 @@
       .Case("sign-ext", HasSignExt)
       .Case("exception-handling", HasExceptionHandling)
       .Case("bulk-memory", HasBulkMemory)
+      .Case("atomics", HasAtomics)
       .Default(false);
 }
 
@@ -68,6 +69,8 @@
     Builder.defineMacro("__wasm_exception_handling__");
   if (HasBulkMemory)
     Builder.defineMacro("__wasm_bulk_memory__");
+  if (HasAtomics)
+    Builder.defineMacro("__wasm_atomics__");
 }
 
 void WebAssemblyTargetInfo::setSIMDLevel(llvm::StringMap<bool> &Features,
@@ -90,6 +93,7 @@
   if (CPU == "bleeding-edge") {
     Features["nontrapping-fptoint"] = true;
     Features["sign-ext"] = true;
+    Features["atomics"] = true;
     setSIMDLevel(Features, SIMD128);
   }
   // Other targets do not consider user-configured features here, but while we
@@ -104,6 +108,8 @@
     Features["exception-handling"] = true;
   if (HasBulkMemory)
     Features["bulk-memory"] = true;
+  if (HasAtomics)
+    Features["atomics"] = true;
 
   return TargetInfo::initFeatureMap(Features, Diags, CPU, FeaturesVec);
 }
@@ -159,6 +165,14 @@
       HasBulkMemory = false;
       continue;
     }
+    if (Feature == "+atomics") {
+      HasAtomics = true;
+      continue;
+    }
+    if (Feature == "-atomics") {
+      HasAtomics = false;
+      continue;
+    }
 
     Diags.Report(diag::err_opt_not_valid_with_opt)
         << Feature << "-target-feature";
Index: cfe/trunk/test/Preprocessor/wasm-target-features.c
===================================================================
--- cfe/trunk/test/Preprocessor/wasm-target-features.c
+++ cfe/trunk/test/Preprocessor/wasm-target-features.c
@@ -53,6 +53,15 @@
 // BULK-MEMORY:#define __wasm_bulk_memory__ 1{{$}}
 //
 // RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm32-unknown-unknown -matomics \
+// RUN:   | FileCheck %s -check-prefix=ATOMICS
+// RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm64-unknown-unknown -matomics \
+// RUN:   | FileCheck %s -check-prefix=ATOMICS
+//
+// ATOMICS:#define __wasm_atomics__ 1{{$}}
+//
+// RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=mvp \
 // RUN:   | FileCheck %s -check-prefix=MVP
 // RUN: %clang -E -dM %s -o - 2>&1 \
@@ -65,6 +74,7 @@
 // MVP-NOT:#define __wasm_sign_ext__
 // MVP-NOT:#define __wasm_exception_handling__
 // MVP-NOT:#define __wasm_bulk_memory__
+// MVP-NOT:#define __wasm_atomics__
 //
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=bleeding-edge \
@@ -73,9 +83,10 @@
 // RUN:     -target wasm64-unknown-unknown -mcpu=bleeding-edge \
 // RUN:   | FileCheck %s -check-prefix=BLEEDING-EDGE
 //
-// BLEEDING-EDGE:#define __wasm_nontrapping_fptoint__ 1{{$}}
-// BLEEDING-EDGE:#define __wasm_sign_ext__ 1{{$}}
-// BLEEDING-EDGE:#define __wasm_simd128__ 1{{$}}
+// BLEEDING-EDGE-DAG:#define __wasm_nontrapping_fptoint__ 1{{$}}
+// BLEEDING-EDGE-DAG:#define __wasm_sign_ext__ 1{{$}}
+// BLEEDING-EDGE-DAG:#define __wasm_simd128__ 1{{$}}
+// BLEEDING-EDGE-DAG:#define __wasm_atomics__ 1{{$}}
 // BLEEDING-EDGE-NOT:#define __wasm_unimplemented_simd128__ 1{{$}}
 //
 // RUN: %clang -E -dM %s -o - 2>&1 \