Recommit r208506: DebugInfo: Include lexical scopes in inlined subroutines.

This was reverted in r208642 due to regressions surrounding file changes
within lexical scopes causing inlining information to be lost.

The issue was in LexicalScopes::getOrCreateInlinedScope, where I was
previously testing "isLexicalBlock" which is false for
"DILexicalBlockFile" (a scope used to represent changes in the current
file name) and assuming it was then a function (breaking out of the
inlined scope path and reaching for the parent non-inlined scopes). By
inverting the condition and testing for "isSubprogram" the correct
behavior is attained.

(also found some weirdness in Clang, see r208742 when reducing this test
case - the resulting test case doesn't apply with the Clang fix, but
I've added a more realistic test case to inline-scopes.ll which does
reproduce the issue and demonstrate the fix)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208748 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LexicalScopes.h

@@ -21,6 +21,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/ValueHandle.h"
@@ -185,9 +186,7 @@ public:
 
   /// findInlinedScope - Find an inlined scope for the given DebugLoc or return
   /// NULL.
-  LexicalScope *findInlinedScope(DebugLoc DL) {
-    return InlinedLexicalScopeMap.lookup(DL);
-  }
+  LexicalScope *findInlinedScope(DebugLoc DL);
 
   /// findLexicalScope - Find regular lexical scope or return null.
   LexicalScope *findLexicalScope(const MDNode *N) {
@@ -230,7 +229,9 @@ private:
 
   /// InlinedLexicalScopeMap - Tracks inlined function scopes in current
   /// function.
-  DenseMap<DebugLoc, LexicalScope *> InlinedLexicalScopeMap;
+  std::unordered_map<std::pair<const MDNode *, const MDNode *>, LexicalScope,
+                     pair_hash<const MDNode *, const MDNode *>>
+  InlinedLexicalScopeMap;
 
   /// AbstractScopeMap - These scopes are  not included LexicalScopeMap.
   // Use an unordered_map to ensure value pointer validity over insertion.