[CodeGen] Devirtualize calls to methods marked final in a derived class

If we see a virtual method call to Base::foo() but can infer that the
object is an instance of Derived, and that 'foo' is marked 'final' in
Derived, we can devirtualize the call to Derived::foo().

Differential Revision: https://reviews.llvm.org/D25813

llvm-svn: 284766

1 files changed, 15 insertions, 7 deletions

diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 4d69c3ff5be..2d70e7a0718 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -2873,6 +2873,11 @@ CodeGenFunction::CanDevirtualizeMemberFunctionCall(const Expr *Base,
   if (getLangOpts().AppleKext)
     return false;
 
+  // If the member function is marked 'final', we know that it can't be
+  // overridden and can therefore devirtualize it.
+  if (MD->hasAttr<FinalAttr>())
+    return true;
+
   // If the most derived class is marked final, we know that no subclass can
   // override this member function and so we can devirtualize it. For example:
   //
@@ -2883,14 +2888,17 @@ CodeGenFunction::CanDevirtualizeMemberFunctionCall(const Expr *Base,
   //   b->f();
   // }
   //
-  const CXXRecordDecl *MostDerivedClassDecl = Base->getBestDynamicClassType();
-  if (MostDerivedClassDecl->hasAttr<FinalAttr>())
-    return true;
+  if (const CXXRecordDecl *BestDynamicDecl = Base->getBestDynamicClassType()) {
+    if (BestDynamicDecl->hasAttr<FinalAttr>())
+      return true;
 
-  // If the member function is marked 'final', we know that it can't be
-  // overridden and can therefore devirtualize it.
-  if (MD->hasAttr<FinalAttr>())
-    return true;
+    // There may be a method corresponding to MD in a derived class. If that
+    // method is marked final, we can devirtualize it.
+    const CXXMethodDecl *DevirtualizedMethod =
+        MD->getCorrespondingMethodInClass(BestDynamicDecl);
+    if (DevirtualizedMethod->hasAttr<FinalAttr>())
+      return true;
+  }
 
   // Similarly, if the class itself is marked 'final' it can't be overridden
   // and we can therefore devirtualize the member function call.