[dart2wasm] Refactor ParameterInfo

- Remove the `Member? member` field:

  - Knowing a `ParameterInfo`s member is not too useful, because it
    doesn't tell us for which use of the member (tear-off getter,
    invocation) the `ParameterInfo` is for.

  - The `member` field has two uses:

    - To compute whether the function being called takes a receiver or
      context parameter.

    - In dispatch table builder: to check whether a selector (via its
      `ParameterInfo`) is for `noSuchMethod`.

    Both of these can be implemented more directly, as done in this CL:

    - Add `final bool takesContextOrReceiver` member to `ParameterInfo`.
    - Add `final bool alwaysAddToDispatchTable` member to `SelectorInfo`
      to handle the special case with `noSuchMethod`.

- Add various assertions in `ParameterInfo` members.

Change-Id: I473657f594c6306605677cf001854407d43f1347
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/398883
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Ömer Ağacan <[email protected]>

Author: osa1

pkg/dart2wasm/lib/dispatch_table.dart

@@ -70,10 +70,16 @@ class SelectorInfo {
   int? offset;
 
   /// The selector's member's name.
-  String get name => paramInfo.member!.name.text;
+  final String name;
 
-  SelectorInfo._(this.translator, this.id, this.callCount, this.paramInfo,
-      {required this.isSetter});
+  /// Whether the selector is for `Object.noSuchMethod`. We introduce instance
+  /// invocations of `noSuchMethod` in dynamic calls, so we always add
+  /// `noSuchMethod` overrides to the dispatch table.
+  final bool isNoSuchMethod;
+
+  SelectorInfo._(
+      this.translator, this.id, this.name, this.callCount, this.paramInfo,
+      {required this.isSetter, required this.isNoSuchMethod});
 
   /// Compute the signature for the functions implementing members targeted by
   /// this selector.
@@ -285,9 +291,10 @@ class DispatchTable {
 
     final selector = _selectorInfo.putIfAbsent(
         selectorId,
-        () => SelectorInfo._(translator, selectorId,
+        () => SelectorInfo._(translator, selectorId, member.name.text,
             _selectorMetadata[selectorId].callCount, paramInfo,
-            isSetter: isSetter));
+            isSetter: isSetter,
+            isNoSuchMethod: member == translator.objectNoSuchMethod));
     assert(selector.isSetter == isSetter);
     selector.hasTearOffUses |= metadata.hasTearOffUses;
     selector.hasNonThisUses |= metadata.hasNonThisUses;
@@ -452,10 +459,7 @@ class DispatchTable {
     // Assign selector offsets
 
     bool isUsedViaDispatchTableCall(SelectorInfo selector) {
-      // Special case for `objectNoSuchMethod`: we introduce instance
-      // invocations of `objectNoSuchMethod` in dynamic calls, so keep it alive
-      // even if there was no references to it from the Dart code.
-      if (selector.paramInfo.member! == translator.objectNoSuchMethod) {
+      if (selector.isNoSuchMethod) {
         return true;
       }
       if (selector.callCount == 0) return false;

pkg/dart2wasm/lib/param_info.dart

@@ -9,19 +9,22 @@ import 'reference_extensions.dart';
 /// Information about optional parameters and their default values for a member
 /// or a set of members belonging to the same override group.
 class ParameterInfo {
-  final Member? member;
-  int typeParamCount = 0;
+  final int typeParamCount;
 
   /// Default values of optional positonal parameters. `positional[i] == null`
   /// means positional parameter `i` is not optional.
-  late final List<Constant?> positional;
+  final List<Constant?> positional;
 
   /// Default values of named parameters. Similar to [positional], `null` means
   /// the the parameter is not optional.
-  late final Map<String, Constant?> named;
+  final Map<String, Constant?> named;
 
-  // Do not access these until the info is complete.
+  final bool takesContextOrReceiver;
+
+  // Dispatch table builder updates `ParameterInfo`s, do not access late fields
+  // until the `ParameterInfo` is complete.
   late final List<String> names = named.keys.toList()..sort();
+
   late final Map<String, int> nameIndex = {
     for (int i = 0; i < names.length; i++) names[i]: positional.length + i
   };
@@ -45,47 +48,66 @@ class ParameterInfo {
     }
   }
 
-  ParameterInfo.fromMember(Reference target) : member = target.asMember {
-    FunctionNode? function = member!.function;
+  ParameterInfo._(this.takesContextOrReceiver, this.typeParamCount,
+      this.positional, this.named);
+
+  factory ParameterInfo.fromMember(Reference target) {
+    final member = target.asMember; // Constructor, Field, or Procedure
+    final function = member.function;
+
     if (target.isTearOffReference) {
-      positional = [];
-      named = {};
-    } else if (function != null) {
-      typeParamCount = (member is Constructor
-              ? member!.enclosingClass!.typeParameters
+      // Tear-off getters don't take type parameters even if the member is
+      // generic.
+      return ParameterInfo._(true, 0, [], {});
+    }
+
+    if (function != null) {
+      // Constructor, or static or instance method.
+      assert(member is Constructor || member is Procedure);
+
+      final typeParamCount = (member is Constructor
+              ? member.enclosingClass.typeParameters
               : function.typeParameters)
           .length;
-      positional = List.generate(function.positionalParameters.length, (i) {
+
+      final positional =
+          List.generate(function.positionalParameters.length, (i) {
         // A required parameter has no default value.
         if (i < function.requiredParameterCount) return null;
         return _defaultValue(function.positionalParameters[i]);
       });
-      named = {
+
+      final named = {
         for (VariableDeclaration param in function.namedParameters)
           param.name!: _defaultValue(param)
       };
-    } else {
-      // A setter parameter has no default value.
-      positional = [if (target.isSetter) null];
-      named = {};
+
+      return ParameterInfo._(
+          member.isInstanceMember, typeParamCount, positional, named);
     }
+
+    // A setter or getter. A setter parameter has no default value.
+    assert(member is Field);
+    return ParameterInfo._(true, 0, [if (target.isSetter) null], {});
   }
 
-  ParameterInfo.fromLocalFunction(FunctionNode function) : member = null {
-    typeParamCount = function.typeParameters.length;
-    positional = List.generate(function.positionalParameters.length, (i) {
+  factory ParameterInfo.fromLocalFunction(FunctionNode function) {
+    final typeParamCount = function.typeParameters.length;
+    final positional = List.generate(function.positionalParameters.length, (i) {
       // A required parameter has no default value.
       if (i < function.requiredParameterCount) return null;
       return _defaultValue(function.positionalParameters[i]);
     });
-    named = {
+    final named = {
       for (VariableDeclaration param in function.namedParameters)
         param.name!: _defaultValue(param)
     };
+    return ParameterInfo._(true, typeParamCount, positional, named);
   }
 
   void merge(ParameterInfo other) {
     assert(typeParamCount == other.typeParamCount);
+    assert(takesContextOrReceiver == other.takesContextOrReceiver);
     for (int i = 0; i < other.positional.length; i++) {
       if (i >= positional.length) {
         positional.add(other.positional[i]);

pkg/dart2wasm/lib/translator.dart

@@ -724,11 +724,6 @@ class Translator with KernelNodes {
   ClosureImplementation getClosure(FunctionNode functionNode,
       w.BaseFunction target, ParameterInfo paramInfo, String name) {
     final targetModule = target.enclosingModule;
-    // The target function takes an extra initial parameter if it's a function
-    // expression / local function (which takes a context) or a tear-off of an
-    // instance method (which takes a receiver).
-    bool takesContextOrReceiver =
-        paramInfo.member == null || paramInfo.member!.isInstanceMember;
 
     // Look up the closure representation for the signature.
     int typeCount = functionNode.typeParameters.length;
@@ -741,7 +736,7 @@ class Translator with KernelNodes {
     assert(positionalCount <= paramInfo.positional.length);
     assert(names.length <= paramInfo.named.length);
     assert(target.type.inputs.length ==
-        (takesContextOrReceiver ? 1 : 0) +
+        (paramInfo.takesContextOrReceiver ? 1 : 0) +
             paramInfo.typeParamCount +
             paramInfo.positional.length +
             paramInfo.named.length);
@@ -805,7 +800,7 @@ class Translator with KernelNodes {
       compilationQueue.add(CompilationTask(
           trampoline,
           _ClosureTrampolineGenerator(this, trampoline, target, typeCount,
-              posArgCount, argNames, paramInfo, takesContextOrReceiver)));
+              posArgCount, argNames, paramInfo)));
       return trampoline;
     }
 
@@ -1394,25 +1389,17 @@ class _ClosureTrampolineGenerator implements CodeGenerator {
   final int posArgCount;
   final List<String> argNames;
   final ParameterInfo paramInfo;
-  final bool takesContextOrReceiver;
-
-  _ClosureTrampolineGenerator(
-      this.translator,
-      this.trampoline,
-      this.target,
-      this.typeCount,
-      this.posArgCount,
-      this.argNames,
-      this.paramInfo,
-      this.takesContextOrReceiver);
+
+  _ClosureTrampolineGenerator(this.translator, this.trampoline, this.target,
+      this.typeCount, this.posArgCount, this.argNames, this.paramInfo);
 
   @override
   void generate(w.InstructionsBuilder b, List<w.Local> paramLocals,
       w.Label? returnLabel) {
     assert(returnLabel == null);
 
     int targetIndex = 0;
-    if (takesContextOrReceiver) {
+    if (paramInfo.takesContextOrReceiver) {
       w.Local receiver = trampoline.locals[0];
       b.local_get(receiver);
       translator.convertType(
@@ -1478,9 +1465,6 @@ class _ClosureDynamicEntryGenerator implements CodeGenerator {
 
     final b = function.body;
 
-    final bool takesContextOrReceiver =
-        paramInfo.member == null || paramInfo.member!.isInstanceMember;
-
     final int typeCount = functionNode.typeParameters.length;
 
     final closureLocal = function.locals[0];
@@ -1500,7 +1484,7 @@ class _ClosureDynamicEntryGenerator implements CodeGenerator {
     int inputIdx = 0;
 
     // Push context or receiver
-    if (takesContextOrReceiver) {
+    if (paramInfo.takesContextOrReceiver) {
       final closureBaseType = w.RefType.def(
           translator.closureLayouter.closureBaseStruct,
           nullable: false);