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/Analysis/ModuleDebugInfoPrinter.cpp b/llvm/lib/Analysis/ModuleDebugInfoPrinter.cpp
index 7ee2f9d..36c4714 100644
--- a/llvm/lib/Analysis/ModuleDebugInfoPrinter.cpp
+++ b/llvm/lib/Analysis/ModuleDebugInfoPrinter.cpp
@@ -72,7 +72,7 @@
   // Printing the nodes directly isn't particularly helpful (since they
   // reference other nodes that won't be printed, particularly for the
   // filenames), so just print a few useful things.
-  for (MDCompileUnit *CU : Finder.compile_units()) {
+  for (DICompileUnit *CU : Finder.compile_units()) {
     O << "Compile unit: ";
     if (const char *Lang = dwarf::LanguageString(CU->getSourceLanguage()))
       O << Lang;
@@ -82,7 +82,7 @@
     O << '\n';
   }
 
-  for (MDSubprogram *S : Finder.subprograms()) {
+  for (DISubprogram *S : Finder.subprograms()) {
     O << "Subprogram: " << S->getName();
     printFile(O, S->getFilename(), S->getDirectory(), S->getLine());
     if (!S->getLinkageName().empty())
@@ -90,7 +90,7 @@
     O << '\n';
   }
 
-  for (const MDGlobalVariable *GV : Finder.global_variables()) {
+  for (const DIGlobalVariable *GV : Finder.global_variables()) {
     O << "Global variable: " << GV->getName();
     printFile(O, GV->getFilename(), GV->getDirectory(), GV->getLine());
     if (!GV->getLinkageName().empty())
@@ -98,12 +98,12 @@
     O << '\n';
   }
 
-  for (const MDType *T : Finder.types()) {
+  for (const DIType *T : Finder.types()) {
     O << "Type:";
     if (!T->getName().empty())
       O << ' ' << T->getName();
     printFile(O, T->getFilename(), T->getDirectory(), T->getLine());
-    if (auto *BT = dyn_cast<MDBasicType>(T)) {
+    if (auto *BT = dyn_cast<DIBasicType>(T)) {
       O << " ";
       if (const char *Encoding =
               dwarf::AttributeEncodingString(BT->getEncoding()))
@@ -117,7 +117,7 @@
       else
         O << "unknown-tag(" << T->getTag() << ")";
     }
-    if (auto *CT = dyn_cast<MDCompositeType>(T)) {
+    if (auto *CT = dyn_cast<DICompositeType>(T)) {
       if (auto *S = CT->getRawIdentifier())
         O << " (identifier: '" << S->getString() << "')";
     }