SILGen: Emit local types with a separate pass instead of while walking statements

Otherwise we might miss emitting a local type that's inside
unreachable code. Normally such a type cannot be found via
name lookup either, but IRGen will walk the list of local types
and try to emit a class with no SIL vtable, which will crash.

Fixes <https://bugs.swift.org/browse/SR-1924>.

Author: slavapestov

lib/SILGen/SILGen.cpp

@@ -1408,6 +1408,9 @@ void SILGenModule::emitSourceFile(SourceFile *sf, unsigned startElem) {
   for (Decl *D : llvm::makeArrayRef(sf->Decls).slice(startElem))
     visit(D);
 
+  for (Decl *D : sf->LocalTypeDecls)
+    visit(D);
+
   // Mark any conformances as "used".
   for (auto conformance : sf->getUsedConformances())
     useConformance(ProtocolConformanceRef(conformance));

lib/SILGen/SILGenFunction.h

@@ -1545,7 +1545,6 @@ class LLVM_LIBRARY_VISIBILITY SILGenFunction
     llvm_unreachable("Not yet implemented");
   }
 
-  void visitNominalTypeDecl(NominalTypeDecl *D);
   void visitFuncDecl(FuncDecl *D);
   void visitPatternBindingDecl(PatternBindingDecl *D);
 
@@ -1554,6 +1553,10 @@ class LLVM_LIBRARY_VISIBILITY SILGenFunction
   std::unique_ptr<Initialization>
   emitPatternBindingInitialization(Pattern *P, JumpDest failureDest);
 
+  void visitNominalTypeDecl(NominalTypeDecl *D) {
+    // No lowering support needed.
+  }
+
   void visitTypeAliasDecl(TypeAliasDecl *D) {
     // No lowering support needed.
   }

lib/SILGen/SILGenType.cpp

@@ -417,10 +417,6 @@ void SILGenModule::visitNominalTypeDecl(NominalTypeDecl *ntd) {
   SILGenType(*this, ntd).emitType();
 }
 
-void SILGenFunction::visitNominalTypeDecl(NominalTypeDecl *ntd) {
-  SILGenType(SGM, ntd).emitType();
-}
-
 /// SILGenExtension - an ASTVisitor for generating SIL from method declarations
 /// and protocol conformances inside type extensions.
 class SILGenExtension : public TypeMemberVisitor<SILGenExtension> {

test/SILGen/local_types.swift

@@ -0,0 +1,10 @@
+// RUN: %target-swift-frontend  -parse-as-library -emit-silgen %s -verify | %FileCheck %s
+// RUN: %target-swift-frontend  -parse-as-library -emit-ir %s
+
+func function() {
+  return
+
+  class UnreachableClass {} // expected-warning {{code after 'return' will never be executed}}
+}
+
+// CHECK-LABEL: sil_vtable UnreachableClass

test/SILGen/mangling_private.swift

@@ -40,7 +40,6 @@ private struct PrivateStruct {
 
 func localTypes() {
   struct LocalStruct {
-    // CHECK-LABEL: sil shared @_TZFVF16mangling_private10localTypesFT_T_L_11LocalStruct13privateMethodfT_T_
     private static func privateMethod() {}
   }
 }
@@ -54,6 +53,7 @@ extension PrivateStruct {
   private func extPrivateMethod() {}
 }
 
+// CHECK-LABEL: sil shared @_TZFVF16mangling_private10localTypesFT_T_L_11LocalStruct13privateMethodfT_T_
 
 // CHECK-LABEL: sil_vtable Sub {
 class Sub : Base {

test/SILGen/types.swift

@@ -33,27 +33,24 @@ struct S {
   }
 
   class SC {
-    // CHECK-LABEL: sil hidden  @_TFCV5types1S2SC3bar{{.*}}
+    // CHECK-LABEL: sil hidden @_TFCV5types1S2SC3bar{{.*}}
     func bar() {}
   }
 }
 
 func f() {
   class FC {
-    // CHECK-LABEL: sil shared @_TFCF5types1fFT_T_L_2FC3zim{{.*}}
     func zim() {}
   }
 }
 
 func g(b b : Bool) {
   if (b) {
     class FC {
-      // CHECK-LABEL: sil shared @_TFCF5types1gFT1bSb_T_L_2FC3zim{{.*}}
       func zim() {}
     }
   } else {
     class FC {
-      // CHECK-LABEL: sil shared @_TFCF5types1gFT1bSb_T_L0_2FC3zim{{.*}}
       func zim() {}
     }
   }
@@ -94,3 +91,7 @@ func referencedFromFunctionEnumFields(_ x: ReferencedFromFunctionEnum)
     return (nil, g)
   }
 }
+
+// CHECK-LABEL: sil shared @_TFCF5types1fFT_T_L_2FC3zim{{.*}}
+// CHECK-LABEL: sil shared @_TFCF5types1gFT1bSb_T_L_2FC3zim{{.*}}
+// CHECK-LABEL: sil shared @_TFCF5types1gFT1bSb_T_L0_2FC3zim{{.*}}