[AST] NFC: Make 'isSelfExpr()' available for general use

Also, generalize the stripping of implicit conversions.

Author: davezarzycki

include/swift/AST/Expr.h

@@ -547,6 +547,10 @@ class alignas(8) Expr {
   /// a builtin operator.
   bool isInfixOperator() const;
 
+  /// Returns true if this is a reference to the implicit self of function.
+  bool isSelfExprOf(const AbstractFunctionDecl *AFD,
+                    bool sameBase = false) const;
+
   /// Produce a mapping from each subexpression to its parent
   /// expression, with the provided expression serving as the root of
   /// the parent map.

lib/AST/Decl.cpp

@@ -5465,21 +5465,6 @@ ConstructorDecl::getDelegatingOrChainedInitKind(DiagnosticEngine *diags,
                                DiagnosticEngine *diags)
         : Decl(decl), Diags(diags) { }
 
-    bool isSelfExpr(Expr *E) {
-      E = E->getSemanticsProvidingExpr();
-
-      if (auto ATSE = dyn_cast<ArchetypeToSuperExpr>(E))
-        E = ATSE->getSubExpr();
-      if (auto IOE = dyn_cast<InOutExpr>(E))
-        E = IOE->getSubExpr();
-      if (auto LE = dyn_cast<LoadExpr>(E))
-        E = LE->getSubExpr();
-      if (auto DRE = dyn_cast<DeclRefExpr>(E))
-        return DRE->getDecl() == Decl->getImplicitSelfDecl();
-
-      return false;
-    }
-
     bool walkToDeclPre(class Decl *D) override {
       // Don't walk into further nominal decls.
       return !isa<NominalTypeDecl>(D);
@@ -5517,7 +5502,7 @@ ConstructorDecl::getDelegatingOrChainedInitKind(DiagnosticEngine *diags,
       BodyInitKind myKind;
       if (arg->isSuperExpr())
         myKind = BodyInitKind::Chained;
-      else if (isSelfExpr(arg))
+      else if (arg->isSelfExprOf(Decl, /*sameBase*/true))
         myKind = BodyInitKind::Delegating;
       else {
         // We're constructing something else.

lib/AST/Expr.cpp

@@ -2164,6 +2164,23 @@ TypeExpr *TypeExpr::createImplicitHack(SourceLoc Loc, Type Ty, ASTContext &C) {
   return Res;
 }
 
+bool Expr::isSelfExprOf(const AbstractFunctionDecl *AFD, bool sameBase) const {
+  auto *E = getSemanticsProvidingExpr();
+
+  if (auto IOE = dyn_cast<InOutExpr>(E))
+    E = IOE->getSubExpr();
+
+  while (auto ICE = dyn_cast<ImplicitConversionExpr>(E)) {
+    if (sameBase && isa<DerivedToBaseExpr>(ICE))
+      return false;
+    E = ICE->getSubExpr();
+  }
+
+  if (auto DRE = dyn_cast<DeclRefExpr>(E))
+    return DRE->getDecl() == AFD->getImplicitSelfDecl();
+
+  return false;
+}
 
 ArchetypeType *OpenExistentialExpr::getOpenedArchetype() const {
   auto type = getOpaqueValue()->getType()->getRValueType();