Index: llvm/include/llvm/IR/Argument.h
===================================================================
--- llvm/include/llvm/IR/Argument.h
+++ llvm/include/llvm/IR/Argument.h
@@ -75,6 +75,10 @@
   /// attribute. These attributes represent arguments being passed by value.
   bool hasPassPointeeByValueAttr() const;
 
+  /// If this argument satisfies has hasPassPointeeByValueAttr, return the
+  /// in-memory ABI size copied to the stack for the call. Otherwise, return 0.
+  uint64_t getPassPointeeByValueCopySize(const DataLayout &DL) const;
+
   /// If this is a byval or inalloca argument, return its alignment.
   /// FIXME: Remove this function once transition to Align is over.
   /// Use getParamAlign() instead.
Index: llvm/lib/IR/Function.cpp
===================================================================
--- llvm/lib/IR/Function.cpp
+++ llvm/lib/IR/Function.cpp
@@ -128,6 +128,27 @@
          Attrs.hasParamAttribute(getArgNo(), Attribute::Preallocated);
 }
 
+uint64_t Argument::getPassPointeeByValueCopySize(const DataLayout &DL) const {
+  AttributeSet ParamAttrs
+    = getParent()->getAttributes().getParamAttributes(getArgNo());
+
+  // FIXME: All the type carrying attributes are mutually exclusive, so there
+  // should be a single query to get the stored type that handles any of them.
+  if (Type *ByValTy = ParamAttrs.getByValType())
+    return DL.getTypeAllocSize(ByValTy);
+  if (Type *PreAllocTy = ParamAttrs.getPreallocatedType())
+    return DL.getTypeAllocSize(PreAllocTy);
+
+  // FIXME: inalloca always depends on pointee element type. It's also possible
+  // for byval to miss it.
+  if (ParamAttrs.hasAttribute(Attribute::InAlloca) ||
+      ParamAttrs.hasAttribute(Attribute::ByVal) ||
+      ParamAttrs.hasAttribute(Attribute::Preallocated))
+    return DL.getTypeAllocSize(cast<PointerType>(getType())->getElementType());
+
+  return 0;
+}
+
 unsigned Argument::getParamAlignment() const {
   assert(getType()->isPointerTy() && "Only pointers have alignments");
   return getParent()->getParamAlignment(getArgNo());
Index: llvm/lib/IR/Mangler.cpp
===================================================================
--- llvm/lib/IR/Mangler.cpp
+++ llvm/lib/IR/Mangler.cpp
@@ -94,15 +94,18 @@
                                const DataLayout &DL) {
   // Calculate arguments size total.
   unsigned ArgWords = 0;
+
+  const unsigned PtrSize = DL.getPointerSize();
+
   for (Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end();
        AI != AE; ++AI) {
-    Type *Ty = AI->getType();
     // 'Dereference' type in case of byval or inalloca parameter attribute.
-    if (AI->hasPassPointeeByValueAttr())
-      Ty = cast<PointerType>(Ty)->getElementType();
+    uint64_t AllocSize = AI->hasPassPointeeByValueAttr() ?
+      AI->getPassPointeeByValueCopySize(DL) :
+      DL.getTypeAllocSize(AI->getType());
+
     // Size should be aligned to pointer size.
-    unsigned PtrSize = DL.getPointerSize();
-    ArgWords += alignTo(DL.getTypeAllocSize(Ty), PtrSize);
+    ArgWords += alignTo(AllocSize, PtrSize);
   }
 
   OS << '@' << ArgWords;