diff --git a/clang/lib/AST/Mangle.cpp b/clang/lib/AST/Mangle.cpp
--- a/clang/lib/AST/Mangle.cpp
+++ b/clang/lib/AST/Mangle.cpp
@@ -50,7 +50,8 @@
   CCM_Fast,
   CCM_RegCall,
   CCM_Vector,
-  CCM_Std
+  CCM_Std,
+  CCM_WasmMainArgcArgv
 };
 
 static bool isExternC(const NamedDecl *ND) {
@@ -63,6 +64,14 @@
                                          const NamedDecl *ND) {
   const TargetInfo &TI = Context.getTargetInfo();
   const llvm::Triple &Triple = TI.getTriple();
+
+  // On wasm, the argc/argv form of "main" is renamed so that the startup code
+  // can call it with the correct function signature.
+  if (Triple.isWasm())
+    if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(ND))
+      if (FD->isMain() && FD->hasPrototype() && FD->param_size() == 2)
+        return CCM_WasmMainArgcArgv;
+
   if (!Triple.isOSWindows() ||
       !(Triple.getArch() == llvm::Triple::x86 ||
         Triple.getArch() == llvm::Triple::x86_64))
@@ -145,6 +154,12 @@
 
   const ASTContext &ASTContext = getASTContext();
   CCMangling CC = getCallingConvMangling(ASTContext, D);
+
+  if (CC == CCM_WasmMainArgcArgv) {
+    Out << "__main_argc_argv";
+    return;
+  }
+
   bool MCXX = shouldMangleCXXName(D);
   const TargetInfo &TI = Context.getTargetInfo();
   if (CC == CCM_Other || (MCXX && TI.getCXXABI() == TargetCXXABI::Microsoft)) {
diff --git a/clang/lib/Frontend/InitHeaderSearch.cpp b/clang/lib/Frontend/InitHeaderSearch.cpp
--- a/clang/lib/Frontend/InitHeaderSearch.cpp
+++ b/clang/lib/Frontend/InitHeaderSearch.cpp
@@ -435,8 +435,7 @@
     break;
 
   case llvm::Triple::UnknownOS:
-    if (triple.getArch() == llvm::Triple::wasm32 ||
-        triple.getArch() == llvm::Triple::wasm64)
+    if (triple.isWasm())
       return;
     break;
   }
diff --git a/clang/test/CodeGen/wasm-call-main.c b/clang/test/CodeGen/wasm-call-main.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/wasm-call-main.c
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -triple wasm32 -o - -emit-llvm %s | FileCheck %s
+
+// Mangle argc/argv main even when it's not defined in this TU.
+
+#include <stddef.h>
+
+int main(int argc, char *argv[]);
+
+int foo(void) {
+    return main(0, NULL);
+}
+
+// CHECK: call i32 @__main_argc_argv(
diff --git a/clang/test/CodeGen/wasm-main.c b/clang/test/CodeGen/wasm-main.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/wasm-main.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple wasm32 -o - -emit-llvm %s | FileCheck %s
+
+// Don't mangle the no-arg form of main.
+
+int main(void) {
+  return 0;
+}
+
+// CHECK-LABEL: define i32 @main()
diff --git a/clang/test/CodeGen/wasm-main_argc_argv.c b/clang/test/CodeGen/wasm-main_argc_argv.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/wasm-main_argc_argv.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple wasm32 -o - -emit-llvm %s | FileCheck %s
+
+// Mangle the argc/argv form of main.
+
+int main(int argc, char **argv) {
+  return 0;
+}
+
+// CHECK-LABEL: define i32 @__main_argc_argv(i32 %argc, i8** %argv)
diff --git a/llvm/include/llvm/ADT/Triple.h b/llvm/include/llvm/ADT/Triple.h
--- a/llvm/include/llvm/ADT/Triple.h
+++ b/llvm/include/llvm/ADT/Triple.h
@@ -730,6 +730,11 @@
     return getArch() == Triple::riscv32 || getArch() == Triple::riscv64;
   }
 
+  /// Tests whether the target is wasm (32- and 64-bit).
+  bool isWasm() const {
+    return getArch() == Triple::wasm32 || getArch() == Triple::wasm64;
+  }
+
   /// Tests whether the target supports comdat
   bool supportsCOMDAT() const {
     return !isOSBinFormatMachO();