Fix MSVC PointerUnion visualization

[mspertus]

Summary

When PointerIntPair was updated to put the IntShift etc. in a helper type, it broke some MSVC visualizations, in particular PointerIntPair and PointerUnion. This patch fixes PointerUnion (PointerIntPair visualization has already been fixed) visualization by adding a local typedef to PointerIntPair so the PointerUnion visualizer can find the IntShift, etc.

While this could have been done in principle without adding the typedef, it not only seems generally useful for debugging, but writing the complex expressions needed without it seem to break the MSVC native visualizer, so this approach seems like a win-win.

As a bonus, we also slightly improve the SmallVector visualizer not to go crazy when visualized before its constructor is called

[mspertus]

Improve PointerUnion expansion to show what type it holds

[aaron.ballman]

This looks great to me (aside from a minor commenting nit). Thank you for the fix!

include/llvm/ADT/PointerIntPair.h

45

Add a full stop to the end of the comment.

include/llvm/ADT/PointerIntPair.h

 /// the bool into bit #2, not bit #0, which allows the low two bits to be used
 /// for something else.  For example, this allows:
 ///   PointerIntPair<PointerIntPair<void*, 1, bool>, 1, bool>
 /// ... and the two bools will land in different bits.
 template <typename PointerTy, unsigned IntBits, typename IntType = unsigned,
           typename PtrTraits = PointerLikeTypeTraits<PointerTy>,
           typename Info = PointerIntPairInfo<PointerTy, IntBits, PtrTraits>>
 class PointerIntPair {
+  // Used by MSVC visualizer but generally helpful for debugging/visualizing
+  using InfoTy = Info;
   intptr_t Value = 0;
 
 public:
   constexpr PointerIntPair() = default;
 
   PointerIntPair(PointerTy PtrVal, IntType IntVal) {
     setPointerAndInt(PtrVal, IntVal);
   }

utils/LLVMVisualizers/llvm.natvis

<Type Name="llvm::SmallVectorImpl&lt;*&gt;">
     <DisplayString IncludeView ="elt2" Condition="Size == 2"></DisplayString>
     <DisplayString IncludeView ="elt2">, {(($T1*)BeginX)[2]}{*this,view(elt3)}</DisplayString>
     <DisplayString IncludeView ="elt3" Condition="Size == 3"></DisplayString>
     <DisplayString IncludeView ="elt3">, {(($T1*)BeginX)[3]}{*this,view(elt4)}</DisplayString>
     <DisplayString IncludeView ="elt4" Condition="Size == 4"></DisplayString>
     <DisplayString IncludeView ="elt4">, /* {Size - 4} more*/ </DisplayString>
     <DisplayString Condition="Size == 0">empty</DisplayString>
     <DisplayString Condition="Size != 0">{{{*this,view(elt0)}}}</DisplayString>
+    <DisplayString>Uninitialized</DisplayString>
     <Expand>
       <Item Name="[size]">Size</Item>
       <Item Name="[capacity]">Capacity</Item>
       <ArrayItems>
         <Size>Size</Size>
         <ValuePointer>($T1*)BeginX</ValuePointer>
       </ArrayItems>
     </Expand>
<Type Name="llvm::PointerIntPair&lt;*,*,*,*&gt;">
     <DisplayString>{$T5::IntMask}: {($T1)(Value &amp; $T5::PointerBitMask)} [{($T3)((Value &gt;&gt; $T5::IntShift) &amp; $T5::IntMask)}]</DisplayString>
     <Expand>
       <Item Name="[ptr]">($T1)(Value &amp; $T5::PointerBitMask)</Item>
       <Item Name="[int]">($T3)((Value &gt;&gt; $T5::IntShift) &amp; $T5::IntMask)</Item>
     </Expand>
   </Type>
 
   <Type Name="llvm::PointerUnion&lt;*,*&gt;">
-    <DisplayString Condition="((Val.Value &gt;&gt; Val.IntShift) &amp; Val.IntMask) == 0">{"$T1", s8b}: {($T1)(Val.Value &amp; Val.PointerBitMask)}</DisplayString>
-    <DisplayString Condition="((Val.Value &gt;&gt; Val.IntShift) &amp; Val.IntMask) != 0">{"$T2", s8b}: {($T2)(Val.Value &amp; Val.PointerBitMask)}</DisplayString>
+    <DisplayString Condition="((Val.Value &gt;&gt; ValTy::InfoTy::IntShift) &amp; ValTy::InfoTy::IntMask) == 0">{"$T1", s8b}: {($T1)(Val.Value &amp; ValTy::InfoTy::PointerBitMask)}</DisplayString>
+    <DisplayString Condition="((Val.Value &gt;&gt; ValTy::InfoTy::IntShift) &amp; ValTy::InfoTy::IntMask) != 0">{"$T2", s8b}: {($T2)(Val.Value &amp; ValTy::InfoTy::PointerBitMask)}</DisplayString>
     <Expand>
-      <ExpandedItem Condition="((Val.Value &gt;&gt; Val.IntShift) &amp; Val.IntMask) == 0">($T1)(Val.Value &amp; Val.PointerBitMask)</ExpandedItem>
-      <ExpandedItem Condition="((Val.Value &gt;&gt; Val.IntShift) &amp; Val.IntMask) != 0">($T2)(Val.Value &amp; Val.PointerBitMask)</ExpandedItem>
+      <Item Name="[Ptr]" Condition="((Val.Value &gt;&gt; ValTy::InfoTy::IntShift) &amp; ValTy::InfoTy::IntMask) == 0">($T1)(Val.Value &amp; ValTy::InfoTy::PointerBitMask)</Item>
+      <Item Name="[Ptr]" Condition="((Val.Value &gt;&gt; ValTy::InfoTy::IntShift) &amp; ValTy::InfoTy::IntMask) != 0">($T2)(Val.Value &amp; ValTy::InfoTy::PointerBitMask)</Item>
     </Expand>
   </Type>
 
   <Type Name="llvm::PointerUnion3&lt;*,*,*&gt;">
     <DisplayString Condition="(Val.Val.Value &amp; 2) != 2 &amp;&amp; (Val.Val.Value &amp; 1) != 1">{"$T1", s8b}: {($T1)((Val.Val.Value &gt;&gt; 2) &lt;&lt; 2)}</DisplayString>
     <DisplayString Condition="(Val.Val.Value &amp; 2) == 2">{"$T2", s8b}: {($T2)((Val.Val.Value &gt;&gt; 2) &lt;&lt; 2)}</DisplayString>
     <DisplayString Condition="(Val.Val.Value &amp; 1) == 1">{"$T3", s8b}: {($T3)((Val.Val.Value &gt;&gt; 2) &lt;&lt; 2)}</DisplayString>
     <Expand>