[StackMaps] Add explicit location size accessor to the stackmap parser

[jacob-hughes]

Summary

The reserved uint8 field in the location block of the stackmap record is used to denote the size of the location.

[reames]

LGTM, thanks for splitting.

p.s. For those reading along, this is parsing the V2 format, not the V3 one in our current documentation. The original patch being split will update all of this to parse V3.

[jacob-hughes]

Updated diff after rebasing from the latest master

llvm/trunk/include/llvm/Object/StackMapParser.h

class LocationAccessor {
     friend class RecordAccessor;
 
   public:
     /// Get the Kind for this location.
     LocationKind getKind() const {
       return LocationKind(P[KindOffset]);
     }
 
+    /// Get the Size for this location.
+    uint8_t getSize() const {
+        return read<uint8_t>(P + SizeOffset);
+
+    }
+
     /// Get the Dwarf register number for this location.
     uint16_t getDwarfRegNum() const {
       return read<uint16_t>(P + DwarfRegNumOffset);
     }
 
     /// Get the small-constant for this location. (Kind must be Constant).
     uint32_t getSmallConstant() const {
       assert(getKind() == LocationKind::Constant && "Not a small constant.");
public:
   private:
     LocationAccessor(const uint8_t *P) : P(P) {}
 
     LocationAccessor next() const {
       return LocationAccessor(P + LocationAccessorSize);
     }
 
     static const int KindOffset = 0;
-    static const int DwarfRegNumOffset = KindOffset + sizeof(uint16_t);
+    static const int SizeOffset = KindOffset + sizeof(uint8_t);
+    static const int DwarfRegNumOffset = SizeOffset + sizeof(uint8_t);
     static const int SmallConstantOffset = DwarfRegNumOffset + sizeof(uint16_t);
     static const int LocationAccessorSize = sizeof(uint64_t);
 
     const uint8_t *P;
   };
 
   /// Accessor for stackmap live-out fields.
   class LiveOutAccessor {