Cache the sized-ness of struct types, once we reach the steady state of

"is sized". This prevents every query to isSized() from recursing over
every sub-type of a struct type. This could get *very* slow for
extremely deep nesting of structs, as in 177.mesa.

This change is a 45% speedup for 'opt -O2' of 177.mesa.linked.bc, and
likely a significant speedup for other cases as well. It even impacts
-O0 cases because so many part of the code try to check whether a type
is sized.

Thanks for the review from Nick Lewycky and Benjamin Kramer on IRC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152197 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/DerivedTypes.h

@@ -195,9 +195,10 @@ class StructType : public CompositeType {
     // This is the contents of the SubClassData field.
     SCDB_HasBody = 1,
     SCDB_Packed = 2,
-    SCDB_IsLiteral = 4
+    SCDB_IsLiteral = 4,
+    SCDB_IsSized = 8
   };
-  
+
   /// SymbolTableEntry - For a named struct that actually has a name, this is a
   /// pointer to the symbol table entry (maintained by LLVMContext) for the
   /// struct.  This is null if the type is an literal struct or if it is
@@ -248,6 +249,9 @@ public:
   /// isOpaque - Return true if this is a type with an identity that has no body
   /// specified yet.  These prints as 'opaque' in .ll files.
   bool isOpaque() const { return (getSubclassData() & SCDB_HasBody) == 0; }
+
+  /// isSized - Return true if this is a sized type.
+  bool isSized() const;
   
   /// hasName - Return true if this is a named struct that has a non-empty name.
   bool hasName() const { return SymbolTableEntry != 0; }