[cfg] Fix handling of unreachable AST in TryCatch and field initializers

Issue: https://github.com/dart-lang/sdk/issues/61635
Change-Id: I189d7d3704c29b1350df23bca174990608b052ad
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/467880
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>

pkg/cfg/lib/front_end/ast_to_ir.dart

@@ -94,7 +94,9 @@ class AstToIr extends ast.RecursiveVisitor {
         _buildImplicitSetter(member as ast.Field);
       case FieldInitializerFunction():
         _translateNode((member as ast.Field).initializer!);
-        builder.addReturn();
+        if (builder.hasOpenBlock) {
+          builder.addReturn();
+        }
       case RegularFunction() || GetterFunction() || SetterFunction():
         _translateNode(member.function?.body);
       case GenerativeConstructor():
@@ -900,8 +902,11 @@ class AstToIr extends ast.RecursiveVisitor {
 
     _translateNode(node.body);
 
-    final done = builder.newJoinBlock();
-    builder.addGoto(done);
+    JoinBlock? done;
+    if (builder.hasOpenBlock) {
+      done = builder.newJoinBlock();
+      builder.addGoto(done);
+    }
     builder.leaveTryBlock();
 
     builder.startBlock(catchBlock);
@@ -950,7 +955,10 @@ class AstToIr extends ast.RecursiveVisitor {
 
       _translateNode(catchClause.body);
 
-      builder.addGoto(done);
+      if (builder.hasOpenBlock) {
+        done ??= builder.newJoinBlock();
+        builder.addGoto(done);
+      }
 
       if (next != null) {
         builder.startBlock(next);
@@ -964,7 +972,9 @@ class AstToIr extends ast.RecursiveVisitor {
       builder.addRethrow();
     }
 
-    builder.startBlock(done);
+    if (done != null) {
+      builder.startBlock(done);
+    }
   }
 
   @override

pkg/cfg/testcases/unreachable_ast.dart

@@ -57,4 +57,38 @@ void unreachableFinally() {
   }
 }
 
+void unreachableTryEnd() {
+  try {
+    print(1);
+    throw 'Bye-bye';
+    print(2);
+  } catch (_) {
+    print(3);
+  }
+}
+
+void unreachableCatchEnd() {
+  try {
+    print(1);
+  } catch (_) {
+    print(2);
+    throw 'Bye-bye';
+    print(3);
+  }
+}
+
+void unreachableBothTryEndAndCatchEnd() {
+  try {
+    print(1);
+    throw 'Bye';
+    print(2);
+  } catch (_) {
+    print(3);
+    throw 'Bye-bye';
+    print(4);
+  }
+}
+
+List<num> unreachableFieldInitializer = [10, 1 + (throw 'Bye') + 2, 20];
+
 void main() {}

pkg/cfg/testcases/unreachable_ast.dart.expect

@@ -97,8 +97,78 @@ B2 = CatchBlock() idom:B0
   DirectCall print(v20)
   Throw(v22)
 
+--- unreachableTryEnd
+B0 = EntryBlock() dominates:(B2, B1)
+  v4 = Constant(1)
+  v6 = Constant("Bye-bye")
+  v8 = Constant(null)
+  v13 = Constant(3)
+  TryEntry(try-body: B1, catch-block: B2)
+B1 = TargetBlock() exception-handler:B2 idom:B0
+  DirectCall print(v4)
+  Throw(v6)
+B2 = CatchBlock() idom:B0
+  Parameter(#exception)
+  Parameter(#stackTrace)
+  DirectCall print(v13)
+  Return(v8)
+
+--- unreachableCatchEnd
+B0 = EntryBlock() dominates:(B2, B1)
+  v4 = Constant(1)
+  v12 = Constant(2)
+  v14 = Constant("Bye-bye")
+  v16 = Constant(null)
+  TryEntry(try-body: B1, catch-block: B2)
+B1 = TargetBlock() exception-handler:B2 idom:B0
+  DirectCall print(v4)
+  Return(v16)
+B2 = CatchBlock() idom:B0
+  Parameter(#exception)
+  Parameter(#stackTrace)
+  DirectCall print(v12)
+  Throw(v14)
+
+--- unreachableBothTryEndAndCatchEnd
+B0 = EntryBlock() dominates:(B2, B1)
+  v4 = Constant(1)
+  v6 = Constant("Bye")
+  Constant(null)
+  v13 = Constant(3)
+  v15 = Constant("Bye-bye")
+  TryEntry(try-body: B1, catch-block: B2)
+B1 = TargetBlock() exception-handler:B2 idom:B0
+  DirectCall print(v4)
+  Throw(v6)
+B2 = CatchBlock() idom:B0
+  Parameter(#exception)
+  Parameter(#stackTrace)
+  DirectCall print(v13)
+  Throw(v15)
+
 --- main
 B0 = EntryBlock()
   v1 = Constant(null)
   Return(v1)
 
+--- getter unreachableFieldInitializer
+B0 = EntryBlock()
+  v1 = LoadStaticField(unreachableFieldInitializer)
+  Return(v1)
+
+--- setter unreachableFieldInitializer
+B0 = EntryBlock()
+  v4 = Constant(null)
+  v1 = Parameter(#value)
+  StoreStaticField(unreachableFieldInitializer, v1)
+  Return(v4)
+
+--- field-init unreachableFieldInitializer
+B0 = EntryBlock()
+  Constant(10)
+  Constant(1)
+  v4 = Constant("Bye")
+  Constant(null)
+  TypeArguments(<num>)
+  Throw(v4)
+