Index: lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
===================================================================
--- lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
+++ lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
@@ -107,14 +107,18 @@
 // I32 vs pointer type) then we don't create a wrapper at all (return nullptr
 // instead).
 //
-// If there is a type mismatch that would result in an invalid wasm module
-// being written then generate wrapper that contains unreachable (i.e. abort
-// at runtime).  Such programs are deep into undefined behaviour territory,
+// If there is a type mismatch that we know would result in an invalid wasm
+// module then generate wrapper that contains unreachable (i.e. abort at 
+// runtime).  Such programs are deep into undefined behaviour territory,
 // but we choose to fail at runtime rather than generate and invalid module
 // or fail at compiler time.  The reason we delay the error is that we want
 // to support the CMake which expects to be able to compile and link programs
 // that refer to functions with entirely incorrect signatures (this is how
 // CMake detects the existence of a function in a toolchain).
+//
+// For bitcasts that involve struct types we don't know at this stage if they
+// would be equivalent at the wasm level and so we can't know if we need to 
+// generate a wrapper.
 static Function *CreateWrapper(Function *F, FunctionType *Ty) {
   Module *M = F->getParent();
 
@@ -132,8 +136,12 @@
   bool TypeMismatch = false;
   bool WrapperNeeded = false;
 
+  Type *ExpectedRtnType = F->getFunctionType()->getReturnType();
+  Type *RtnType = Ty->getReturnType();
+
   if ((F->getFunctionType()->getNumParams() != Ty->getNumParams()) ||
-      (F->getFunctionType()->isVarArg() != Ty->isVarArg()))
+      (F->getFunctionType()->isVarArg() != Ty->isVarArg()) ||
+      (ExpectedRtnType != RtnType))
     WrapperNeeded = true;
 
   for (; AI != AE && PI != PE; ++AI, ++PI) {
@@ -148,6 +156,10 @@
             CastInst::CreateBitOrPointerCast(AI, ParamType, "cast");
         BB->getInstList().push_back(PtrCast);
         Args.push_back(PtrCast);
+      } else if (ArgType->isStructTy() || ParamType->isStructTy()) {
+        LLVM_DEBUG(dbgs() << "CreateWrapper: struct param type in bitcast: "
+                          << F->getName() << "\n");
+        WrapperNeeded = false;
       } else {
         LLVM_DEBUG(dbgs() << "CreateWrapper: arg type mismatch calling: "
                           << F->getName() << "\n");
@@ -159,7 +171,7 @@
     }
   }
 
-  if (!TypeMismatch) {
+  if (WrapperNeeded && !TypeMismatch) {
     for (; PI != PE; ++PI)
       Args.push_back(UndefValue::get(*PI));
     if (F->isVarArg())
@@ -173,10 +185,9 @@
     // Determine what value to return.
     if (RtnType->isVoidTy()) {
       ReturnInst::Create(M->getContext(), BB);
-      WrapperNeeded = true;
     } else if (ExpectedRtnType->isVoidTy()) {
+      LLVM_DEBUG(dbgs() << "Creating dummy return: " << *RtnType << "\n");
       ReturnInst::Create(M->getContext(), UndefValue::get(RtnType), BB);
-      WrapperNeeded = true;
     } else if (RtnType == ExpectedRtnType) {
       ReturnInst::Create(M->getContext(), Call, BB);
     } else if (CastInst::isBitOrNoopPointerCastable(ExpectedRtnType, RtnType,
@@ -185,6 +196,10 @@
           CastInst::CreateBitOrPointerCast(Call, RtnType, "cast");
       BB->getInstList().push_back(Cast);
       ReturnInst::Create(M->getContext(), Cast, BB);
+    } else if (RtnType->isStructTy() || ExpectedRtnType->isStructTy()) {
+      LLVM_DEBUG(dbgs() << "CreateWrapper: struct return type in bitcast: "
+                        << F->getName() << "\n");
+      WrapperNeeded = false;
     } else {
       LLVM_DEBUG(dbgs() << "CreateWrapper: return type mismatch calling: "
                         << F->getName() << "\n");
@@ -195,6 +210,10 @@
   }
 
   if (TypeMismatch) {
+    // Create a new wrapper that simply contains `unreachable`.
+    Wrapper->eraseFromParent();
+    Wrapper = Function::Create(Ty, Function::PrivateLinkage, F->getName() + "_bitcast_invalid", M);
+    BasicBlock *BB = BasicBlock::Create(M->getContext(), "body", Wrapper);
     new UnreachableInst(M->getContext(), BB);
     Wrapper->setName(F->getName() + "_bitcast_invalid");
   } else if (!WrapperNeeded) {
@@ -203,6 +222,7 @@
     Wrapper->eraseFromParent();
     return nullptr;
   }
+  LLVM_DEBUG(dbgs() << "CreateWrapper: " << F->getName() << "\n");
   return Wrapper;
 }
 
Index: test/CodeGen/WebAssembly/function-bitcasts.ll
===================================================================
--- test/CodeGen/WebAssembly/function-bitcasts.ll
+++ test/CodeGen/WebAssembly/function-bitcasts.ll
@@ -6,6 +6,7 @@
 target triple = "wasm32-unknown-unknown"
 
 declare void @has_i32_arg(i32)
+declare void @has_struct_arg({i32})
 declare i32 @has_i32_ret()
 declare void @vararg(...)
 declare void @plain(i32)
@@ -16,9 +17,10 @@
 declare void @foo3()
 
 ; CHECK-LABEL: test:
-; CHECK-NEXT: call        .Lhas_i32_arg_bitcast@FUNCTION{{$}}
-; CHECK-NEXT: call        .Lhas_i32_arg_bitcast@FUNCTION{{$}}
+; CHECK-NEXT: call        .Lhas_i32_arg_bitcast.2@FUNCTION{{$}}
+; CHECK-NEXT: call        .Lhas_i32_arg_bitcast.2@FUNCTION{{$}}
 ; CHECK-NEXT: call        .Lhas_i32_ret_bitcast@FUNCTION{{$}}
+; CHECK-NEXT: i32.call     $drop=, has_i32_ret@FUNCTION
 ; CHECK-NEXT: i32.const   $push[[L0:[0-9]+]]=, 0
 ; CHECK-NEXT: call        .Lfoo0_bitcast@FUNCTION, $pop[[L0]]{{$}}
 ; CHECK-NEXT: i32.const   $push[[L1:[0-9]+]]=, 0
@@ -36,6 +38,7 @@
   call void bitcast (void (i32)* @has_i32_arg to void ()*)()
   call void bitcast (void (i32)* @has_i32_arg to void ()*)()
   call void bitcast (i32 ()* @has_i32_ret to void ()*)()
+  call i32 bitcast (i32 ()* @has_i32_ret to i32 ()*)()
   call void bitcast (void ()* @foo0 to void (i32)*)(i32 0)
   %p = bitcast void ()* @foo0 to void (i32)*
   call void %p(i32 0)
@@ -51,6 +54,30 @@
   ret void
 }
 
+; CHECK-LABEL: test_structs:
+; CHECK: call     .Lhas_i32_arg_bitcast.1@FUNCTION, $pop{{[0-9]+}}, $pop{{[0-9]+$}}
+; CHECK: call     .Lhas_i32_arg_bitcast@FUNCTION, $0, $pop2
+; CHECK: call     .Lhas_struct_arg_bitcast@FUNCTION{{$}}
+define void @test_structs() {
+entry:
+  call void bitcast (void (i32)* @has_i32_arg to void (i32, {i32})*)(i32 5, {i32} {i32 6})
+  call {i32, i64} bitcast (void (i32)* @has_i32_arg to {i32, i64} (i32)*)(i32 7)
+  call void bitcast (void ({i32})* @has_struct_arg to void ()*)()
+  ret void
+}
+
+; CHECK-LABEL: test_structs_unhandled:
+; CHECK: call    has_struct_arg@FUNCTION, $pop{{[0-9]+$}}
+; CHECK: call    has_struct_arg@FUNCTION, $pop{{[0-9]+$}}
+; CHECK: call    has_i32_ret@FUNCTION, $pop{{[0-9]+$}}
+define void @test_structs_unhandled() {
+entry:
+  call void @has_struct_arg({i32} {i32 3})
+  call void bitcast (void ({i32})* @has_struct_arg to void ({i64})*)({i64} {i64 4})
+  call {i32, i32} bitcast (i32 ()* @has_i32_ret to {i32, i32} ()*)()
+  ret void
+}
+
 ; CHECK-LABEL: test_varargs:
 ; CHECK:      set_global
 ; CHECK:      i32.const   $push[[L3:[0-9]+]]=, 0{{$}}
@@ -113,7 +140,7 @@
 ; CHECK:      i32.const   $push[[L3:[0-9]+]]=, call_func@FUNCTION{{$}}
 ; CHECK-NEXT: i32.const   $push[[L2:[0-9]+]]=, has_i32_arg@FUNCTION{{$}}
 ; CHECK-NEXT: call        "__invoke_void_i32()*"@FUNCTION, $pop[[L3]], $pop[[L2]]{{$}}
-; CHECK:      i32.const   $push[[L4:[0-9]+]]=, .Lhas_i32_arg_bitcast@FUNCTION{{$}}
+; CHECK:      i32.const   $push[[L4:[0-9]+]]=, .Lhas_i32_arg_bitcast.2@FUNCTION{{$}}
 ; CHECK-NEXT: call        __invoke_void@FUNCTION, $pop[[L4]]{{$}}
 declare i32 @personality(...)
 define void @test_invoke() personality i32 (...)* @personality {
@@ -139,6 +166,16 @@
 }
 
 ; CHECK-LABEL: .Lhas_i32_arg_bitcast:
+; CHECK-NEXT: .param      i32, i32
+; CHECK-NEXT: call        has_i32_arg@FUNCTION, $1{{$}}
+; CHECK-NEXT: end_function
+
+; CHECK-LABEL: .Lhas_i32_arg_bitcast.1:
+; CHECK-NEXT: .param      i32, i32
+; CHECK-NEXT: call        has_i32_arg@FUNCTION, $0{{$}}
+; CHECK-NEXT: end_function
+
+; CHECK-LABEL: .Lhas_i32_arg_bitcast.2:
 ; CHECK-NEXT: call        has_i32_arg@FUNCTION, $0{{$}}
 ; CHECK-NEXT: end_function
 
Index: test/CodeGen/WebAssembly/unsupported-function-bitcasts.ll
===================================================================
--- test/CodeGen/WebAssembly/unsupported-function-bitcasts.ll
+++ test/CodeGen/WebAssembly/unsupported-function-bitcasts.ll
@@ -9,28 +9,31 @@
 declare i32 @has_i64_arg(i64)
 declare i32 @has_ptr_arg(i8*)
 
+; CHECK-LABEL: test_invalid_rtn:
+; CHECK-NEXT: i32.const   $push[[L0:[0-9]+]]=, 0{{$}}
+; CHECK-NEXT: i32.call $push[[L1:[0-9]+]]=, .Lhas_i64_arg_bitcast_invalid.2@FUNCTION, $pop[[L0]]{{$}}
+; CHECK-NEXT: drop $pop[[L1]]{{$}}
+; CHECK-NEXT: i64.const   $push[[L0:[0-9]+]]=, 0{{$}}
+; CHECK-NEXT: i64.call $push[[L1:[0-9]+]]=, .Lhas_i64_arg_bitcast_invalid@FUNCTION, $pop[[L0]]{{$}}
+; CHECK-NEXT: drop $pop[[L1]]{{$}}
+; CHECK-NEXT: end_function
 define void @test_invalid_rtn() {
 entry:
   call i32 bitcast (i32 (i64)* @has_i64_arg to i32 (i32)*)(i32 0)
+  call [1 x i64] bitcast (i32 (i64)* @has_i64_arg to [1 x i64] (i64)*)(i64 0)
   ret void
 }
-; CHECK-LABEL: test_invalid_rtn:
-; CHECK-NEXT: i32.const   $push[[L0:[0-9]+]]=, 0{{$}}
-; CHECK-NEXT: i32.call $push1=, .Lhas_i64_arg_bitcast_invalid@FUNCTION, $pop[[L0]]{{$}}
-; CHECK-NEXT: drop $pop1
-; CHECK-NEXT: end_function
 
-define void @test_invalid_arg() {
-entry:
-  call i32 bitcast (i32 (i8*)* @has_ptr_arg to i32 (i8)*)(i8 2)
-  call i32 bitcast (i32 (i8*)* @has_ptr_arg to i32 (i32)*)(i32 2)
-  call i32 bitcast (i32 (i8*)* @has_ptr_arg to i32 (i64)*)(i64 3)
+; CHECK-LABEL: test_struct_rtn:
+; CHECK: 	call    	has_i64_arg@FUNCTION, $pop6, $pop0
+define void @test_struct_rtn() {
+  call {i32, i32} bitcast (i32 (i64)* @has_i64_arg to {i32, i32} (i64)*)(i64 0)
   ret void
 }
 
 ; CHECK-LABEL: test_invalid_arg:
 ; CHECK-NEXT: 	i32.const	$push[[L0:[0-9]+]]=, 2{{$}}
-; CHECK-NEXT: 	i32.call	$push[[L1:[0-9]+]]=, .Lhas_ptr_arg_bitcast_invalid.1@FUNCTION, $pop[[L0]]{{$}}
+; CHECK-NEXT: 	i32.call	$push[[L1:[0-9]+]]=, .Lhas_ptr_arg_bitcast_invalid.4@FUNCTION, $pop[[L0]]{{$}}
 ; CHECK-NEXT: 	drop	$pop[[L1]]{{$}}
 ; CHECK-NEXT: 	i32.const	$push[[L0:[0-9]+]]=, 2{{$}}
 ; CHECK-NEXT: 	i32.call	$push[[L1:[0-9]+]]=, has_ptr_arg@FUNCTION, $pop[[L0]]{{$}}
@@ -39,8 +42,21 @@
 ; CHECK-NEXT: 	i32.call	$push[[L1:[0-9]+]]=, .Lhas_ptr_arg_bitcast_invalid@FUNCTION, $pop[[L0]]{{$}}
 ; CHECK-NEXT: 	drop	$pop[[L1]]{{$}}
 ; CHECK-NEXT: 	end_function
+define void @test_invalid_arg() {
+entry:
+  call i32 bitcast (i32 (i8*)* @has_ptr_arg to i32 (i8)*)(i8 2)
+  call i32 bitcast (i32 (i8*)* @has_ptr_arg to i32 (i32)*)(i32 2)
+  call i32 bitcast (i32 (i8*)* @has_ptr_arg to i32 (i64)*)(i64 3)
+  ret void
+}
 
 ; CHECK-LABEL: .Lhas_i64_arg_bitcast_invalid:
+; CHECK-NEXT:  .param  	i64
+; CHECK-NEXT:  .result 	i64
+; CHECK-NEXT:  unreachable
+; CHECK-NEXT:  end_function
+
+; CHECK-LABEL: .Lhas_i64_arg_bitcast_invalid.2:
 ; CHECK-NEXT:  .param  	i32
 ; CHECK-NEXT:  .result 	i32
 ; CHECK-NEXT:  unreachable
@@ -52,7 +68,7 @@
 ; CHECK-NEXT: 	unreachable
 ; CHECK-NEXT: 	end_function
 
-; CHECK-LABEL: .Lhas_ptr_arg_bitcast_invalid.1:
+; CHECK-LABEL: .Lhas_ptr_arg_bitcast_invalid.4:
 ; CHECK-NEXT: 	.param  	i32
 ; CHECK-NEXT: 	.result 	i32
 ; CHECK-NEXT: 	unreachable