[llvm] r205358 - Add a comment about the DIDescriptor class hierarchy.

[Adrian Prantl]

Author: adrian
Date: Tue Apr  1 16:04:24 2014
New Revision: 205358

URL: http://llvm.org/viewvc/llvm-project?rev=205358&view=rev
Log:
Add a comment about the DIDescriptor class hierarchy.

Modified:
    llvm/trunk/include/llvm/IR/DebugInfo.h
    llvm/trunk/lib/IR/DebugInfo.cpp

Modified: llvm/trunk/include/llvm/IR/DebugInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/DebugInfo.h?rev=205358&r1=205357&r2=205358&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/DebugInfo.h (original)
+++ llvm/trunk/include/llvm/IR/DebugInfo.h Tue Apr  1 16:04:24 2014
@@ -197,6 +197,13 @@ typedef DIRef<DIScope> DIScopeRef;
 typedef DIRef<DIType> DITypeRef;
 
 /// DIScope - A base class for various scopes.
+///
+/// Although, implementation-wise, DIScope is the parent class of most
+/// other DIxxx classes, including DIType and its descendants, most of
+/// DIScope’s descendants are not a substitutable subtype of
+/// DIScope. The DIDescriptor::isScope() method only is true for
+/// DIScopes that are scopes in the strict lexical scope sense
+/// (DICompileUnit, DISubprogram, etc.), but not for, e.g., a DIType.
 class DIScope : public DIDescriptor {
 protected:
   friend class DIDescriptor;

Modified: llvm/trunk/lib/IR/DebugInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/DebugInfo.cpp?rev=205358&r1=205357&r2=205358&view=diff
==============================================================================
--- llvm/trunk/lib/IR/DebugInfo.cpp (original)
+++ llvm/trunk/lib/IR/DebugInfo.cpp Tue Apr  1 16:04:24 2014
@@ -429,8 +429,10 @@ static bool fieldIsTypeRef(const MDNode
 /// Check if a value can be a ScopeRef.
 static bool isScopeRef(const Value *Val) {
   return !Val ||
-         (isa<MDString>(Val) && !cast<MDString>(Val)->getString().empty()) ||
-         isa<MDNode>(Val);
+    (isa<MDString>(Val) && !cast<MDString>(Val)->getString().empty()) ||
+    // Not checking for Val->isScope() here, because it would work
+    // only for lexical scopes and not all subclasses of DIScope.
+    isa<MDNode>(Val);
 }
 
 /// Check if a field at position Elt of a MDNode can be a ScopeRef.