IR: Give 'DI' prefix to debug info metadata

Finish off PR23080 by renaming the debug info IR constructs from `MD*`
to `DI*`.  The last of the `DIDescriptor` classes were deleted in
r235356, and the last of the related typedefs removed in r235413, so
this has all baked for about a week.

Note: If you have out-of-tree code (like a frontend), I recommend that
you get everything compiling and tests passing with the *previous*
commit before updating to this one.  It'll be easier to keep track of
what code is using the `DIDescriptor` hierarchy and what you've already
updated, and I think you're extremely unlikely to insert bugs.  YMMV of
course.

Back to *this* commit: I did this using the rename-md-di-nodes.sh
upgrade script I've attached to PR23080 (both code and testcases) and
filtered through clang-format-diff.py.  I edited the tests for
test/Assembler/invalid-generic-debug-node-*.ll by hand since the columns
were off-by-three.  It should work on your out-of-tree testcases (and
code, if you've followed the advice in the previous paragraph).

Some of the tests are in badly named files now (e.g.,
test/Assembler/invalid-mdcompositetype-missing-tag.ll should be
'dicompositetype'); I'll come back and move the files in a follow-up
commit.

llvm-svn: 236120
diff --git a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
index 125aab2..e9f6239 100644
--- a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
+++ b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
@@ -174,14 +174,14 @@
   for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
     BasicBlock *B = I;
     TerminatorInst *Last = B->getTerminator();
-    const MDLocation *LastDIL = Last->getDebugLoc();
+    const DILocation *LastDIL = Last->getDebugLoc();
     if (!LastDIL)
       continue;
 
     for (unsigned I = 0; I < Last->getNumSuccessors(); ++I) {
       BasicBlock *Succ = Last->getSuccessor(I);
       Instruction *First = Succ->getFirstNonPHIOrDbgOrLifetime();
-      const MDLocation *FirstDIL = First->getDebugLoc();
+      const DILocation *FirstDIL = First->getDebugLoc();
       if (!FirstDIL)
         continue;
 
@@ -197,7 +197,7 @@
         auto *File = Builder.createFile(Filename, Scope->getDirectory());
 
         // FIXME: Calculate the discriminator here, based on local information,
-        // and delete MDLocation::computeNewDiscriminator().  The current
+        // and delete DILocation::computeNewDiscriminator().  The current
         // solution gives different results depending on other modules in the
         // same context.  All we really need is to discriminate between
         // FirstDIL and LastDIL -- a local map would suffice.
@@ -205,7 +205,7 @@
         auto *NewScope =
             Builder.createLexicalBlockFile(Scope, File, Discriminator);
         auto *NewDIL =
-            MDLocation::get(Ctx, FirstDIL->getLine(), FirstDIL->getColumn(),
+            DILocation::get(Ctx, FirstDIL->getLine(), FirstDIL->getColumn(),
                             NewScope, FirstDIL->getInlinedAt());
         DebugLoc newDebugLoc = NewDIL;