diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -3629,6 +3629,8 @@
 
 .. option:: -mtail-call, -mno-tail-call
 
+.. option:: -mextended-const, -mno-extended-const
+
 WebAssembly Driver
 ------------------
 .. option:: -mexec-model=<arg>
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3468,6 +3468,8 @@
 def mno_tail_call : Flag<["-"], "mno-tail-call">, Group<m_wasm_Features_Group>;
 def mreference_types : Flag<["-"], "mreference-types">, Group<m_wasm_Features_Group>;
 def mno_reference_types : Flag<["-"], "mno-reference-types">, Group<m_wasm_Features_Group>;
+def mextended_const : Flag<["-"], "mextended-const">, Group<m_wasm_Features_Group>;
+def mno_extended_const : Flag<["-"], "mno-extended-const">, Group<m_wasm_Features_Group>;
 def mexec_model_EQ : Joined<["-"], "mexec-model=">, Group<m_wasm_Features_Driver_Group>,
                      Values<"command,reactor">,
                      HelpText<"Execution model (WebAssembly only)">;
diff --git a/clang/lib/Basic/Targets/WebAssembly.h b/clang/lib/Basic/Targets/WebAssembly.h
--- a/clang/lib/Basic/Targets/WebAssembly.h
+++ b/clang/lib/Basic/Targets/WebAssembly.h
@@ -39,6 +39,7 @@
   bool HasMultivalue = false;
   bool HasTailCall = false;
   bool HasReferenceTypes = false;
+  bool HasExtendedConst = false;
 
   std::string ABI;
 
diff --git a/clang/lib/Basic/Targets/WebAssembly.cpp b/clang/lib/Basic/Targets/WebAssembly.cpp
--- a/clang/lib/Basic/Targets/WebAssembly.cpp
+++ b/clang/lib/Basic/Targets/WebAssembly.cpp
@@ -56,6 +56,7 @@
       .Case("multivalue", HasMultivalue)
       .Case("tail-call", HasTailCall)
       .Case("reference-types", HasReferenceTypes)
+      .Case("extended-const", HasExtendedConst)
       .Default(false);
 }
 
@@ -93,6 +94,8 @@
     Builder.defineMacro("__wasm_tail_call__");
   if (HasReferenceTypes)
     Builder.defineMacro("__wasm_reference_types__");
+  if (HasExtendedConst)
+    Builder.defineMacro("__wasm_extended_const__");
 }
 
 void WebAssemblyTargetInfo::setSIMDLevel(llvm::StringMap<bool> &Features,
@@ -240,6 +243,14 @@
       HasReferenceTypes = false;
       continue;
     }
+    if (Feature == "+extended-const") {
+      HasExtendedConst = true;
+      continue;
+    }
+    if (Feature == "-extended-const") {
+      HasExtendedConst = false;
+      continue;
+    }
 
     Diags.Report(diag::err_opt_not_valid_with_opt)
         << Feature << "-target-feature";
diff --git a/clang/test/Preprocessor/wasm-target-features.c b/clang/test/Preprocessor/wasm-target-features.c
--- a/clang/test/Preprocessor/wasm-target-features.c
+++ b/clang/test/Preprocessor/wasm-target-features.c
@@ -105,6 +105,15 @@
 // RUN:   | FileCheck %s -check-prefix=REFERENCE-TYPES
 //
 // REFERENCE-TYPES:#define __wasm_reference_types__ 1{{$}}
+//
+// RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm32-unknown-unknown -mextended-const \
+// RUN:   | FileCheck %s -check-prefix=EXTENDED-CONST
+// RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm64-unknown-unknown -mextended-const \
+// RUN:   | FileCheck %s -check-prefix=EXTENDED-CONST
+//
+// EXTENDED-CONST:#define __wasm_extended_const__ 1{{$}}
 
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=mvp \
@@ -123,6 +132,7 @@
 // MVP-NOT:#define __wasm_multivalue__
 // MVP-NOT:#define __wasm_tail_call__
 // MVP-NOT:#define __wasm_reference_types__
+// MVP-NOT:#define __wasm_extended_const__
 
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=bleeding-edge \
@@ -142,6 +152,7 @@
 // BLEEDING-EDGE-NOT:#define __wasm_exception_handling__ 1{{$}}
 // BLEEDING-EDGE-NOT:#define __wasm_multivalue__ 1{{$}}
 // BLEEDING-EDGE-NOT:#define __wasm_reference_types__ 1{{$}}
+// BLEEDING-EDGE-NOT:#define __wasm_extended_const__ 1{{$}}
 
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=bleeding-edge -mno-simd128 \
diff --git a/llvm/lib/Target/WebAssembly/WebAssembly.td b/llvm/lib/Target/WebAssembly/WebAssembly.td
--- a/llvm/lib/Target/WebAssembly/WebAssembly.td
+++ b/llvm/lib/Target/WebAssembly/WebAssembly.td
@@ -67,6 +67,10 @@
       SubtargetFeature<"reference-types", "HasReferenceTypes", "true",
                        "Enable reference types">;
 
+def FeatureExtendedConst :
+      SubtargetFeature<"extended-const", "HasExtendedConst", "true",
+                       "Enable extended const expressions">;
+
 //===----------------------------------------------------------------------===//
 // Architectures.
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
@@ -66,6 +66,10 @@
     Predicate<"Subtarget->hasReferenceTypes()">,
     AssemblerPredicate<(all_of FeatureReferenceTypes), "reference-types">;
 
+def HasExtendedConst :
+    Predicate<"Subtarget->hasExtendedConst()">,
+    AssemblerPredicate<(all_of FeatureExtendedConst), "extended-const">;
+
 //===----------------------------------------------------------------------===//
 // WebAssembly-specific DAG Node Types.
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblySubtarget.h b/llvm/lib/Target/WebAssembly/WebAssemblySubtarget.h
--- a/llvm/lib/Target/WebAssembly/WebAssemblySubtarget.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblySubtarget.h
@@ -48,6 +48,7 @@
   bool HasMutableGlobals = false;
   bool HasTailCall = false;
   bool HasReferenceTypes = false;
+  bool HasExtendedConst = false;
 
   /// What processor and OS we're targeting.
   Triple TargetTriple;