Index: llvm/trunk/include/llvm/Target/TargetLowering.h
===================================================================
--- llvm/trunk/include/llvm/Target/TargetLowering.h
+++ llvm/trunk/include/llvm/Target/TargetLowering.h
@@ -2827,6 +2827,9 @@
     // TargetLowering::LowerCall that perform tail call conversions.
     bool IsTailCall = false;
 
+    // Is Call lowering done post SelectionDAG type legalization.
+    bool IsPostTypeLegalization = false;
+
     unsigned NumFixedArgs = -1;
     CallingConv::ID CallConv = CallingConv::C;
     SDValue Callee;
@@ -2949,6 +2952,11 @@
       return *this;
     }
 
+    CallLoweringInfo &setIsPostTypeLegalization(bool Value=true) {
+      IsPostTypeLegalization = Value;
+      return *this;
+    }
+
     ArgListTy &getArgs() {
       return Args;
     }
Index: llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1991,7 +1991,8 @@
                     std::move(Args))
       .setTailCall(isTailCall)
       .setSExtResult(isSigned)
-      .setZExtResult(!isSigned);
+      .setZExtResult(!isSigned)
+      .setIsPostTypeLegalization(true);
 
   std::pair<SDValue, SDValue> CallInfo = TLI.LowerCallTo(CLI);
 
@@ -2029,7 +2030,8 @@
       .setLibCallee(TLI.getLibcallCallingConv(LC), RetTy, Callee,
                     std::move(Args))
       .setSExtResult(isSigned)
-      .setZExtResult(!isSigned);
+      .setZExtResult(!isSigned)
+      .setIsPostTypeLegalization(true);
 
   std::pair<SDValue,SDValue> CallInfo = TLI.LowerCallTo(CLI);
 
@@ -3565,16 +3567,10 @@
         SDValue Args[] = { HiLHS, LHS, HiRHS, RHS };
         Ret = ExpandLibCall(LC, WideVT, Args, 4, isSigned, dl);
       }
-      BottomHalf = DAG.getNode(ISD::EXTRACT_ELEMENT, dl, VT, Ret,
-                               DAG.getIntPtrConstant(0, dl));
-      TopHalf = DAG.getNode(ISD::EXTRACT_ELEMENT, dl, VT, Ret,
-                            DAG.getIntPtrConstant(1, dl));
-      // Ret is a node with an illegal type. Because such things are not
-      // generally permitted during this phase of legalization, make sure the
-      // node has no more uses. The above EXTRACT_ELEMENT nodes should have been
-      // folded.
-      assert(Ret->use_empty() &&
-             "Unexpected uses of illegally type from expanded lib call.");
+      assert(Ret.getOpcode() == ISD::MERGE_VALUES &&
+             "Ret value is a collection of constituent nodes holding result.");
+      BottomHalf = Ret.getOperand(0);
+      TopHalf = Ret.getOperand(1);
     }
 
     if (isSigned) {
Index: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -7842,6 +7842,22 @@
   auto &DL = CLI.DAG.getDataLayout();
   ComputeValueVTs(*this, DL, CLI.RetTy, RetTys, &Offsets);
 
+  if (CLI.IsPostTypeLegalization) {
+    // If we are lowering a libcall after legalization, split the return type.
+    SmallVector<EVT, 4> OldRetTys = std::move(RetTys);
+    SmallVector<uint64_t, 4> OldOffsets = std::move(Offsets);
+    for (size_t i = 0, e = OldRetTys.size(); i != e; ++i) {
+      EVT RetVT = OldRetTys[i];
+      uint64_t Offset = OldOffsets[i];
+      MVT RegisterVT = getRegisterType(CLI.RetTy->getContext(), RetVT);
+      unsigned NumRegs = getNumRegisters(CLI.RetTy->getContext(), RetVT);
+      unsigned RegisterVTSize = RegisterVT.getSizeInBits();
+      RetTys.append(NumRegs, RegisterVT);
+      for (unsigned j = 0; j != NumRegs; ++j)
+        Offsets.push_back(Offset + j * RegisterVTSize);
+    }
+  }
+
   SmallVector<ISD::OutputArg, 4> Outs;
   GetReturnInfo(CLI.RetTy, getReturnAttrs(CLI), Outs, *this, DL);
 
@@ -7924,6 +7940,7 @@
   for (unsigned i = 0, e = Args.size(); i != e; ++i) {
     SmallVector<EVT, 4> ValueVTs;
     ComputeValueVTs(*this, DL, Args[i].Ty, ValueVTs);
+    // FIXME: Split arguments if CLI.IsPostTypeLegalization
     Type *FinalType = Args[i].Ty;
     if (Args[i].IsByVal)
       FinalType = cast<PointerType>(Args[i].Ty)->getElementType();
Index: llvm/trunk/test/CodeGen/WebAssembly/umulo-i64.ll
===================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/umulo-i64.ll
+++ llvm/trunk/test/CodeGen/WebAssembly/umulo-i64.ll
@@ -0,0 +1,21 @@
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
+; Test that UMULO works correctly on 64-bit operands.
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-emscripten"
+
+; CHECK-LABEL: _ZN4core3num21_$LT$impl$u20$u64$GT$15overflowing_mul17h07be88b4cbac028fE:
+; CHECK:     __multi3
+; Function Attrs: inlinehint
+define void @"_ZN4core3num21_$LT$impl$u20$u64$GT$15overflowing_mul17h07be88b4cbac028fE"(i64, i64) unnamed_addr #0 {
+start:
+  %2 = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 %0, i64 %1)
+  %3 = extractvalue { i64, i1 } %2, 0
+  store i64 %3, i64* undef
+  unreachable
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare { i64, i1 } @llvm.umul.with.overflow.i64(i64, i64) #1
+
+attributes #0 = { inlinehint }
+attributes #1 = { nounwind readnone speculatable }