Refactor cast<>'s in if conditionals, which can only assert on failure.

Summary:
This patch refactors several instances of cast<> used in if
conditionals.  Since cast<> asserts on failure, the else branch can
never be taken.

In some cases, the fix is to replace cast<> with dyn_cast<>.  While
others required the removal of the conditional and some minor
refactoring.

A discussion can be seen here: http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20190318/265044.html

Differential Revision: https://reviews.llvm.org/D59529

llvm-svn: 356441

1 files changed, 6 insertions, 4 deletions

diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index e1b5161b027..2f7bb5333a3 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -1179,13 +1179,15 @@ DeclContext *DeclContext::getPrimaryContext() {
     return this;
 
   case Decl::ObjCInterface:
-    if (auto *Def = cast<ObjCInterfaceDecl>(this)->getDefinition())
-      return Def;
+    if (auto *OID = dyn_cast<ObjCInterfaceDecl>(this))
+      if (auto *Def = OID->getDefinition())
+        return Def;
     return this;
 
   case Decl::ObjCProtocol:
-    if (auto *Def = cast<ObjCProtocolDecl>(this)->getDefinition())
-      return Def;
+    if (auto *OPD = dyn_cast<ObjCProtocolDecl>(this))
+      if (auto *Def = OPD->getDefinition())
+        return Def;
     return this;
 
   case Decl::ObjCCategory: