Revert r73790, and replace it with a significantly less ugly solution. Rather than trying to make the global reader-writer lock work,

create separate recursive mutexes for each value map.  The recursive-ness fixes the double-acquiring issue, which having one per ValueMap
lets us continue to maintain some concurrency.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73801 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Constant.h

@@ -61,7 +61,7 @@ protected:
 public:
   /// Static constructor to get a '0' constant of arbitrary type...
   ///
-  static Constant *getNullValue(const Type *Ty, bool locked = true);
+  static Constant *getNullValue(const Type *Ty);
 
   /// Static constructor to get a '-1' constant.  This supports integers and
   /// vectors.
@@ -107,9 +107,7 @@ public:
   /// available cached constants.  Implementations should call
   /// destroyConstantImpl as the last thing they do, to destroy all users and
   /// delete this.
-  virtual void destroyConstant(bool locked = true) {
-    assert(0 && "Not reached!");
-  }
+  virtual void destroyConstant() { assert(0 && "Not reached!"); }
 
   //// Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const Constant *) { return true; }