Index: cfe/trunk/include/clang/Driver/Options.td
===================================================================
--- cfe/trunk/include/clang/Driver/Options.td
+++ cfe/trunk/include/clang/Driver/Options.td
@@ -2177,6 +2177,8 @@
 def mno_atomics : Flag<["-"], "mno-atomics">, 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 mmutable_globals : Flag<["-"], "mmutable-globals">, Group<m_wasm_Features_Group>;
+def mno_mutable_globals : Flag<["-"], "mno-mutable-globals">, 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
@@ -35,6 +35,7 @@
   bool HasExceptionHandling = false;
   bool HasBulkMemory = false;
   bool HasAtomics = false;
+  bool HasMutableGlobals = 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
@@ -42,6 +42,7 @@
       .Case("exception-handling", HasExceptionHandling)
       .Case("bulk-memory", HasBulkMemory)
       .Case("atomics", HasAtomics)
+      .Case("mutable-globals", HasMutableGlobals)
       .Default(false);
 }
 
@@ -71,6 +72,8 @@
     Builder.defineMacro("__wasm_bulk_memory__");
   if (HasAtomics)
     Builder.defineMacro("__wasm_atomics__");
+  if (HasMutableGlobals)
+    Builder.defineMacro("__wasm_mutable_globals__");
 }
 
 void WebAssemblyTargetInfo::setSIMDLevel(llvm::StringMap<bool> &Features,
@@ -94,6 +97,7 @@
     Features["nontrapping-fptoint"] = true;
     Features["sign-ext"] = true;
     Features["atomics"] = true;
+    Features["mutable-globals"] = true;
     setSIMDLevel(Features, SIMD128);
   }
   // Other targets do not consider user-configured features here, but while we
@@ -110,6 +114,8 @@
     Features["bulk-memory"] = true;
   if (HasAtomics)
     Features["atomics"] = true;
+  if (HasMutableGlobals)
+    Features["mutable-globals"] = true;
 
   return TargetInfo::initFeatureMap(Features, Diags, CPU, FeaturesVec);
 }
@@ -173,6 +179,14 @@
       HasAtomics = false;
       continue;
     }
+    if (Feature == "+mutable-globals") {
+      HasMutableGlobals = true;
+      continue;
+    }
+    if (Feature == "-mutable-globals") {
+      HasMutableGlobals = 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
@@ -71,6 +71,15 @@
 // PTHREAD:#define __wasm_atomics__ 1{{$}}
 
 // RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm32-unknown-unknown -mmutable-globals \
+// RUN:   | FileCheck %s -check-prefix=MUTABLE-GLOBALS
+// RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm64-unknown-unknown -mmutable-globals \
+// RUN:   | FileCheck %s -check-prefix=MUTABLE-GLOBALS
+//
+// MUTABLE-GLOBALS:#define __wasm_mutable_globals__ 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 \
@@ -84,6 +93,7 @@
 // MVP-NOT:#define __wasm_exception_handling__
 // MVP-NOT:#define __wasm_bulk_memory__
 // MVP-NOT:#define __wasm_atomics__
+// MVP-NOT:#define __wasm_mutable_globals__
 
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=bleeding-edge \
@@ -96,6 +106,7 @@
 // BLEEDING-EDGE-DAG:#define __wasm_sign_ext__ 1{{$}}
 // BLEEDING-EDGE-DAG:#define __wasm_simd128__ 1{{$}}
 // BLEEDING-EDGE-DAG:#define __wasm_atomics__ 1{{$}}
+// BLEEDING-EDGE-DAG:#define __wasm_mutable_globals__ 1{{$}}
 // BLEEDING-EDGE-NOT:#define __wasm_unimplemented_simd128__ 1{{$}}
 
 // RUN: %clang -E -dM %s -o - 2>&1 \
Index: llvm/trunk/lib/Target/WebAssembly/WebAssembly.td
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssembly.td
+++ llvm/trunk/lib/Target/WebAssembly/WebAssembly.td
@@ -51,6 +51,10 @@
       SubtargetFeature<"bulk-memory", "HasBulkMemory", "true",
                        "Enable bulk memory operations">;
 
+def FeatureMutableGlobals :
+      SubtargetFeature<"mutable-globals", "HasMutableGlobals", "true",
+                       "Enable mutable globals">;
+
 //===----------------------------------------------------------------------===//
 // Architectures.
 //===----------------------------------------------------------------------===//
Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblySubtarget.h
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblySubtarget.h
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblySubtarget.h
@@ -44,6 +44,7 @@
   bool HasSignExt = false;
   bool HasExceptionHandling = false;
   bool HasBulkMemory = false;
+  bool HasMutableGlobals = false;
 
   /// String name of used CPU.
   std::string CPUString;
@@ -97,6 +98,7 @@
   bool hasSignExt() const { return HasSignExt; }
   bool hasExceptionHandling() const { return HasExceptionHandling; }
   bool hasBulkMemory() const { return HasBulkMemory; }
+  bool hasMutableGlobals() const { return HasMutableGlobals; }
 
   /// Parses features string setting specified subtarget options. Definition of
   /// function is auto generated by tblgen.
Index: llvm/trunk/test/CodeGen/WebAssembly/mutable-globals.ll
===================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/mutable-globals.ll
+++ llvm/trunk/test/CodeGen/WebAssembly/mutable-globals.ll
@@ -0,0 +1,16 @@
+; RUN: llc < %s -mattr=+mutable-globals | FileCheck %s
+
+; Test that mutable globals is properly emitted into the target features section
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+define void @foo() {
+  ret void
+}
+
+; CHECK-LABEL: .custom_section.target_features
+; CHECK-NEXT: .int8 1
+; CHECK-NEXT: .int8 43
+; CHECK-NEXT: .int8 15
+; CHECK-NEXT: .ascii "mutable-globals"