Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -674,13 +674,16 @@
   if (IsVarArg) {
     // Outgoing non-fixed arguments are placed in a buffer. First
     // compute their offsets and the total amount of buffer space needed.
-    for (SDValue Arg :
-         make_range(OutVals.begin() + NumFixedArgs, OutVals.end())) {
+    for (unsigned I = NumFixedArgs; I < Outs.size(); ++I) {
+      const ISD::OutputArg &Out = Outs[I];
+      SDValue &Arg = OutVals[I];
       EVT VT = Arg.getValueType();
       assert(VT != MVT::iPTR && "Legalized args should be concrete");
       Type *Ty = VT.getTypeForEVT(*DAG.getContext());
+      unsigned Align = std::max(Out.Flags.getOrigAlign(),
+                                Layout.getABITypeAlignment(Ty));
       unsigned Offset = CCInfo.AllocateStack(Layout.getTypeAllocSize(Ty),
-                                             Layout.getABITypeAlignment(Ty));
+                                             Align);
       CCInfo.addLoc(CCValAssign::getMem(ArgLocs.size(), VT.getSimpleVT(),
                                         Offset, VT.getSimpleVT(),
                                         CCValAssign::Full));
Index: llvm/trunk/test/CodeGen/WebAssembly/varargs.ll
===================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/varargs.ll
+++ llvm/trunk/test/CodeGen/WebAssembly/varargs.ll
@@ -163,6 +163,32 @@
   ret void
 }
 
+; Test that an fp128 argument is properly aligned and allocated
+; within a vararg buffer.
+
+; CHECK-LABEL: call_fp128_alignment:
+; CHECK:      global.get      $push7=, __stack_pointer
+; CHECK-NEXT: i32.const       $push8=, 32
+; CHECK-NEXT: i32.sub         $push12=, $pop7, $pop8
+; CHECK-NEXT: local.tee       $push11=, $1=, $pop12
+; CHECK-NEXT: global.set      __stack_pointer, $pop11
+; CHECK-NEXT: i32.const       $push0=, 24
+; CHECK-NEXT: i32.add         $push1=, $1, $pop0
+; CHECK-NEXT: i64.const       $push2=, -9223372036854775808
+; CHECK-NEXT: i64.store       0($pop1), $pop2
+; CHECK-NEXT: i32.const       $push3=, 16
+; CHECK-NEXT: i32.add         $push4=, $1, $pop3
+; CHECK-NEXT: i64.const       $push5=, 1
+; CHECK-NEXT: i64.store       0($pop4), $pop5
+; CHECK-NEXT: i32.const       $push6=, 7
+; CHECK-NEXT: i32.store       0($1), $pop6
+; CHECK-NEXT: call            callee, $1
+define void @call_fp128_alignment(i8* %p) {
+entry:
+  call void (...) @callee(i8 7, fp128 0xL00000000000000018000000000000000)
+  ret void
+}
+
 declare void @llvm.va_start(i8*)
 declare void @llvm.va_end(i8*)
 declare void @llvm.va_copy(i8*, i8*)