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/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 8441696..d289406 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5978,7 +5978,7 @@
 SDDbgValue *SelectionDAG::getDbgValue(MDNode *Var, MDNode *Expr, SDNode *N,
                                       unsigned R, bool IsIndirect, uint64_t Off,
                                       DebugLoc DL, unsigned O) {
-  assert(cast<MDLocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
+  assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
          "Expected inlined-at fields to agree");
   return new (Allocator) SDDbgValue(Var, Expr, N, R, IsIndirect, Off, DL, O);
 }
@@ -5987,7 +5987,7 @@
 SDDbgValue *SelectionDAG::getConstantDbgValue(MDNode *Var, MDNode *Expr,
                                               const Value *C, uint64_t Off,
                                               DebugLoc DL, unsigned O) {
-  assert(cast<MDLocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
+  assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
          "Expected inlined-at fields to agree");
   return new (Allocator) SDDbgValue(Var, Expr, C, Off, DL, O);
 }
@@ -5996,7 +5996,7 @@
 SDDbgValue *SelectionDAG::getFrameIndexDbgValue(MDNode *Var, MDNode *Expr,
                                                 unsigned FI, uint64_t Off,
                                                 DebugLoc DL, unsigned O) {
-  assert(cast<MDLocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
+  assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
          "Expected inlined-at fields to agree");
   return new (Allocator) SDDbgValue(Var, Expr, FI, Off, DL, O);
 }