Index: llvm/include/llvm/ADT/APFloat.h
===================================================================
--- llvm/include/llvm/ADT/APFloat.h
+++ llvm/include/llvm/ADT/APFloat.h
@@ -777,6 +777,7 @@
   APFloat(const fltSemantics &Semantics) : U(Semantics) {}
   APFloat(const fltSemantics &Semantics, StringRef S);
   APFloat(const fltSemantics &Semantics, integerPart I) : U(Semantics, I) {}
+  // TODO: Remove this constructor. This isn't faster than the first one.
   APFloat(const fltSemantics &Semantics, uninitializedTag)
       : U(Semantics, uninitialized) {}
   APFloat(const fltSemantics &Semantics, const APInt &I) : U(Semantics, I) {}
Index: llvm/lib/Support/APFloat.cpp
===================================================================
--- llvm/lib/Support/APFloat.cpp
+++ llvm/lib/Support/APFloat.cpp
@@ -818,7 +818,10 @@
   sign = false;
 }
 
-IEEEFloat::IEEEFloat(const fltSemantics &ourSemantics, uninitializedTag tag) {
+// Delegate to the previous constructor, because later copy constructor may
+// actually inspects category, which can't be garbage.
+IEEEFloat::IEEEFloat(const fltSemantics &ourSemantics, uninitializedTag tag)
+    : IEEEFloat(ourSemantics) {
   // Allocates storage if necessary but does not initialize it.
   initialize(&ourSemantics);
 }
@@ -3877,7 +3880,9 @@
 
 DoubleAPFloat::DoubleAPFloat(const DoubleAPFloat &RHS)
     : Semantics(RHS.Semantics),
-      Floats(new APFloat[2]{APFloat(RHS.Floats[0]), APFloat(RHS.Floats[1])}) {
+      Floats(RHS.Floats ? new APFloat[2]{APFloat(RHS.Floats[0]),
+                                         APFloat(RHS.Floats[1])}
+                        : nullptr) {
   assert(Semantics == &PPCDoubleDouble);
 }
 
@@ -3888,7 +3893,7 @@
 }
 
 DoubleAPFloat &DoubleAPFloat::operator=(const DoubleAPFloat &RHS) {
-  if (Semantics == RHS.Semantics) {
+  if (Semantics == RHS.Semantics && RHS.Floats) {
     Floats[0] = RHS.Floats[0];
     Floats[1] = RHS.Floats[1];
   } else if (this != &RHS) {