Index: lib/CodeGen/TargetInfo.cpp
===================================================================
--- lib/CodeGen/TargetInfo.cpp
+++ lib/CodeGen/TargetInfo.cpp
@@ -720,10 +720,12 @@
 // This is a very simple ABI that relies a lot on DefaultABIInfo.
 //===----------------------------------------------------------------------===//
 
-class WebAssemblyABIInfo final : public DefaultABIInfo {
+class WebAssemblyABIInfo final : public SwiftABIInfo {
+  DefaultABIInfo defaultInfo;
+
 public:
   explicit WebAssemblyABIInfo(CodeGen::CodeGenTypes &CGT)
-      : DefaultABIInfo(CGT) {}
+      : SwiftABIInfo(CGT), defaultInfo(CGT) {}
 
 private:
   ABIArgInfo classifyReturnType(QualType RetTy) const;
@@ -741,6 +743,15 @@
 
   Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                     QualType Ty) const override;
+
+  bool shouldPassIndirectlyForSwift(ArrayRef<llvm::Type*> scalars,
+                                    bool asReturnValue) const override {
+    return occupiesMoreThan(CGT, scalars, /*total*/ 4);
+  }
+
+  bool isSwiftErrorInRegister() const override {
+    return false;
+  }
 };
 
 class WebAssemblyTargetCodeGenInfo final : public TargetCodeGenInfo {
@@ -778,7 +789,7 @@
   }
 
   // Otherwise just do the default thing.
-  return DefaultABIInfo::classifyArgumentType(Ty);
+  return defaultInfo.classifyArgumentType(Ty);
 }
 
 ABIArgInfo WebAssemblyABIInfo::classifyReturnType(QualType RetTy) const {
@@ -798,7 +809,7 @@
   }
 
   // Otherwise just do the default thing.
-  return DefaultABIInfo::classifyReturnType(RetTy);
+  return defaultInfo.classifyReturnType(RetTy);
 }
 
 Address WebAssemblyABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
@@ -8307,7 +8318,7 @@
 }
 
 ABIArgInfo ARCABIInfo::getIndirectByValue(QualType Ty) const {
-  // Compute the byval alignment. 
+  // Compute the byval alignment.
   const unsigned MinABIStackAlignInBytes = 4;
   unsigned TypeAlign = getContext().getTypeAlign(Ty) / 8;
   return ABIArgInfo::getIndirect(CharUnits::fromQuantity(4), /*ByVal=*/true,
@@ -8371,7 +8382,7 @@
   if (RetTy->isAnyComplexType())
     return ABIArgInfo::getDirectInReg();
 
-  // Arguments of size > 4 registers are indirect.  
+  // Arguments of size > 4 registers are indirect.
   auto RetSize = llvm::alignTo(getContext().getTypeSize(RetTy), 32) / 32;
   if (RetSize > 4)
     return getIndirectByRef(RetTy, /*HasFreeRegs*/ true);