Devirtualize destructor of final class.

Summary:
Take advantage of the final keyword to devirtualize destructor calls.

Fix https://bugs.llvm.org/show_bug.cgi?id=21368

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: davidxl, Prazek, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D63161

llvm-svn: 364100

Author: hjyamauchi

clang/lib/CodeGen/CGExprCXX.cpp

@@ -1865,9 +1865,33 @@ static void EmitObjectDelete(CodeGenFunction &CGF,
       Dtor = RD->getDestructor();
 
       if (Dtor->isVirtual()) {
-        CGF.CGM.getCXXABI().emitVirtualObjectDelete(CGF, DE, Ptr, ElementType,
-                                                    Dtor);
-        return;
+        bool UseVirtualCall = true;
+        const Expr *Base = DE->getArgument();
+        if (auto *DevirtualizedDtor =
+                dyn_cast_or_null<const CXXDestructorDecl>(
+                    Dtor->getDevirtualizedMethod(
+                        Base, CGF.CGM.getLangOpts().AppleKext))) {
+          UseVirtualCall = false;
+          const CXXRecordDecl *DevirtualizedClass =
+              DevirtualizedDtor->getParent();
+          if (declaresSameEntity(getCXXRecord(Base), DevirtualizedClass)) {
+            // Devirtualized to the class of the base type (the type of the
+            // whole expression).
+            Dtor = DevirtualizedDtor;
+          } else {
+            // Devirtualized to some other type. Would need to cast the this
+            // pointer to that type but we don't have support for that yet, so
+            // do a virtual call. FIXME: handle the case where it is
+            // devirtualized to the derived type (the type of the inner
+            // expression) as in EmitCXXMemberOrOperatorMemberCallExpr.
+            UseVirtualCall = true;
+          }
+        }
+        if (UseVirtualCall) {
+          CGF.CGM.getCXXABI().emitVirtualObjectDelete(CGF, DE, Ptr, ElementType,
+                                                      Dtor);
+          return;
+        }
       }
     }
   }

clang/test/CodeGenCXX/devirtualize-dtor-final.cpp

@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown -std=c++11 %s -emit-llvm -o - | FileCheck %s
+
+namespace Test1 {
+  struct A { virtual ~A() {} };
+  struct B final : A {};
+  struct C : A { virtual ~C() final {} };
+  struct D { virtual ~D() final = 0; };
+  // CHECK-LABEL: define void @_ZN5Test13fooEPNS_1BE
+  void foo(B *b) {
+    // CHECK: call void @_ZN5Test11BD1Ev
+    delete b;
+  }
+  // CHECK-LABEL: define void @_ZN5Test14foo2EPNS_1CE
+  void foo2(C *c) {
+    // CHECK: call void @_ZN5Test11CD1Ev
+    delete c;
+  }
+  // CHECK-LABEL: define void @_ZN5Test14evilEPNS_1DE
+  void evil(D *p) {
+    // CHECK-NOT: call void @_ZN5Test11DD1Ev
+    delete p;
+  }
+}