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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@356441 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AST/ASTImporter.cpp

@@ -8460,44 +8460,41 @@ Error ASTImporter::ImportDefinition_New(Decl *From) {
   if (!To)
     return llvm::make_error<ImportError>();
 
-  if (auto *FromDC = cast<DeclContext>(From)) {
-    ASTNodeImporter Importer(*this);
+  auto *FromDC = cast<DeclContext>(From);
+  ASTNodeImporter Importer(*this);
 
-    if (auto *ToRecord = dyn_cast<RecordDecl>(To)) {
-      if (!ToRecord->getDefinition()) {
-        return Importer.ImportDefinition(
-            cast<RecordDecl>(FromDC), ToRecord,
-            ASTNodeImporter::IDK_Everything);
-      }
+  if (auto *ToRecord = dyn_cast<RecordDecl>(To)) {
+    if (!ToRecord->getDefinition()) {
+      return Importer.ImportDefinition(
+          cast<RecordDecl>(FromDC), ToRecord,
+          ASTNodeImporter::IDK_Everything);
     }
+  }
 
-    if (auto *ToEnum = dyn_cast<EnumDecl>(To)) {
-      if (!ToEnum->getDefinition()) {
-        return Importer.ImportDefinition(
-            cast<EnumDecl>(FromDC), ToEnum, ASTNodeImporter::IDK_Everything);
-      }
+  if (auto *ToEnum = dyn_cast<EnumDecl>(To)) {
+    if (!ToEnum->getDefinition()) {
+      return Importer.ImportDefinition(
+          cast<EnumDecl>(FromDC), ToEnum, ASTNodeImporter::IDK_Everything);
     }
+  }
 
-    if (auto *ToIFace = dyn_cast<ObjCInterfaceDecl>(To)) {
-      if (!ToIFace->getDefinition()) {
-        return Importer.ImportDefinition(
-            cast<ObjCInterfaceDecl>(FromDC), ToIFace,
-            ASTNodeImporter::IDK_Everything);
-      }
+  if (auto *ToIFace = dyn_cast<ObjCInterfaceDecl>(To)) {
+    if (!ToIFace->getDefinition()) {
+      return Importer.ImportDefinition(
+          cast<ObjCInterfaceDecl>(FromDC), ToIFace,
+          ASTNodeImporter::IDK_Everything);
     }
+  }
 
-    if (auto *ToProto = dyn_cast<ObjCProtocolDecl>(To)) {
-      if (!ToProto->getDefinition()) {
-        return Importer.ImportDefinition(
-            cast<ObjCProtocolDecl>(FromDC), ToProto,
-            ASTNodeImporter::IDK_Everything);
-      }
+  if (auto *ToProto = dyn_cast<ObjCProtocolDecl>(To)) {
+    if (!ToProto->getDefinition()) {
+      return Importer.ImportDefinition(
+          cast<ObjCProtocolDecl>(FromDC), ToProto,
+          ASTNodeImporter::IDK_Everything);
     }
-
-    return Importer.ImportDeclContext(FromDC, true);
   }
 
-  return Error::success();
+  return Importer.ImportDeclContext(FromDC, true);
 }
 
 void ASTImporter::ImportDefinition(Decl *From) {

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:

lib/CodeGen/CGExprConstant.cpp

@@ -1698,31 +1698,20 @@ ConstantLValueEmitter::tryEmitAbsolute(llvm::Type *destTy) {
   auto offset = getOffset();
 
   // If we're producing a pointer, this is easy.
-  if (auto destPtrTy = cast<llvm::PointerType>(destTy)) {
-    if (Value.isNullPointer()) {
-      // FIXME: integer offsets from non-zero null pointers.
-      return CGM.getNullPointer(destPtrTy, DestType);
-    }
-
-    // Convert the integer to a pointer-sized integer before converting it
-    // to a pointer.
-    // FIXME: signedness depends on the original integer type.
-    auto intptrTy = CGM.getDataLayout().getIntPtrType(destPtrTy);
-    llvm::Constant *C = offset;
-    C = llvm::ConstantExpr::getIntegerCast(getOffset(), intptrTy,
-                                           /*isSigned*/ false);
-    C = llvm::ConstantExpr::getIntToPtr(C, destPtrTy);
-    return C;
-  }
-
-  // Otherwise, we're basically returning an integer constant.
-
-  // FIXME: this does the wrong thing with ptrtoint of a null pointer,
-  // but since we don't know the original pointer type, there's not much
-  // we can do about it.
-
-  auto C = getOffset();
-  C = llvm::ConstantExpr::getIntegerCast(C, destTy, /*isSigned*/ false);
+  auto destPtrTy = cast<llvm::PointerType>(destTy);
+  if (Value.isNullPointer()) {
+    // FIXME: integer offsets from non-zero null pointers.
+    return CGM.getNullPointer(destPtrTy, DestType);
+  }
+
+  // Convert the integer to a pointer-sized integer before converting it
+  // to a pointer.
+  // FIXME: signedness depends on the original integer type.
+  auto intptrTy = CGM.getDataLayout().getIntPtrType(destPtrTy);
+  llvm::Constant *C = offset;
+  C = llvm::ConstantExpr::getIntegerCast(getOffset(), intptrTy,
+                                         /*isSigned*/ false);
+  C = llvm::ConstantExpr::getIntToPtr(C, destPtrTy);
   return C;
 }
 

lib/CodeGen/MicrosoftCXXABI.cpp

@@ -735,7 +735,7 @@ public:
         CGM.CreateRuntimeFunction(FTy, "_CxxThrowException");
     // _CxxThrowException is stdcall on 32-bit x86 platforms.
     if (CGM.getTarget().getTriple().getArch() == llvm::Triple::x86) {
-      if (auto *Fn = cast<llvm::Function>(Throw.getCallee()))
+      if (auto *Fn = dyn_cast<llvm::Function>(Throw.getCallee()))
         Fn->setCallingConv(llvm::CallingConv::X86_StdCall);
     }
     return Throw;

lib/Sema/SemaOpenMP.cpp

@@ -10901,7 +10901,7 @@ buildDeclareReductionRef(Sema &SemaRef, SourceLocation Loc, SourceRange Range,
     for (NamedDecl *D : ULE->decls()) {
       if (D == PrevD)
         Lookups.push_back(UnresolvedSet<8>());
-      else if (auto *DRD = cast<OMPDeclareReductionDecl>(D))
+      else if (auto *DRD = dyn_cast<OMPDeclareReductionDecl>(D))
         Lookups.back().addDecl(DRD);
       PrevD = D;
     }