Introduce enum values for previously defined metadata types. (NFC)

Our metadata scheme lazily assigns IDs to string metadata, but we have a mechanism to preassign them as well.  Using a preassigned ID is helpful since we get compile time type checking, and avoid some (minimal) string construction and comparison.  This change adds enum value for three existing metadata types:
+    MD_nontemporal = 9, // "nontemporal"
+    MD_mem_parallel_loop_access = 10, // "llvm.mem.parallel_loop_access"
+    MD_nonnull = 11 // "nonnull"

I went through an updated various uses as well.  I made no attempt to get all uses; I focused on the ones which were easily grepable and easily to translate.  For example, there were several items in LoopInfo.cpp I chose not to update.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220248 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -329,6 +329,8 @@ static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewT
     case LLVMContext::MD_invariant_load:
     case LLVMContext::MD_alias_scope:
     case LLVMContext::MD_noalias:
+    case LLVMContext::MD_nontemporal:
+    case LLVMContext::MD_mem_parallel_loop_access:
       // All of these directly apply.
       NewLoad->setMetadata(ID, N);
       break;
@@ -339,12 +341,6 @@ static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewT
       break;
     }
   }
-  // FIXME: These metadata nodes should really have enumerators and be handled
-  // above.
-  if (MDNode *N = LI.getMetadata("nontemporal"))
-    NewLoad->setMetadata("nontemporal", N);
-  if (MDNode *N = LI.getMetadata("llvm.mem.parallel_loop_access"))
-    NewLoad->setMetadata("llvm.mem.parallel_loop_access", N);
   return NewLoad;
 }