[dart2wasm] Generate local names in the names section

Local names for function value parameters and for "precise this", return
values are generated, state indices in `async` and `sync*` functions are
generated.

We can generate names for more locals as needed.

Change-Id: Ie919f030f0bfae8adbca90408509dd04a7414278
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/419200
Commit-Queue: Ömer Ağacan <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>

Author: osa1

pkg/dart2wasm/lib/async.dart

@@ -26,8 +26,9 @@ mixin AsyncCodeGeneratorMixin on StateMachineEntryAstCodeGenerator {
 
     // (1) Create async state.
 
-    final asyncStateLocal =
-        b.addLocal(w.RefType(asyncSuspendStateInfo.struct, nullable: false));
+    final asyncStateLocal = b.addLocal(
+        w.RefType(asyncSuspendStateInfo.struct, nullable: false),
+        name: "asyncState");
 
     // AsyncResumeFun _resume
     translator.globals.readGlobal(b, translator.makeFunctionRef(resumeFun));
@@ -195,13 +196,16 @@ class AsyncStateMachineCodeGenerator extends StateMachineCodeGenerator {
     Context? localContext = context;
     while (localContext != null) {
       if (!localContext.isEmpty) {
-        localContext.currentLocal =
-            b.addLocal(w.RefType.def(localContext.struct, nullable: true));
+        localContext.currentLocal = b.addLocal(
+            w.RefType.def(localContext.struct, nullable: true),
+            name: "context");
         if (localContext.containsThis) {
           assert(thisLocal == null);
-          thisLocal = b.addLocal(localContext
-              .struct.fields[localContext.thisFieldIndex].type.unpacked
-              .withNullability(false));
+          thisLocal = b.addLocal(
+              localContext
+                  .struct.fields[localContext.thisFieldIndex].type.unpacked
+                  .withNullability(false),
+              name: "this");
           translator
               .getDummyValuesCollectorForModule(b.module)
               .instantiateDummyValue(b, thisLocal!.type);
@@ -214,7 +218,7 @@ class AsyncStateMachineCodeGenerator extends StateMachineCodeGenerator {
     }
 
     // Read target index from the suspend state.
-    targetIndexLocal = addLocal(w.NumType.i32);
+    targetIndexLocal = addLocal(w.NumType.i32, name: "targetIndex");
     b.local_get(_suspendStateLocal);
     b.struct_get(
         asyncSuspendStateInfo.struct, FieldIndex.asyncSuspendStateTargetIndex);

pkg/dart2wasm/lib/code_generator.dart

@@ -115,9 +115,8 @@ abstract class AstCodeGenerator
 
   w.ValueType translateType(DartType type) => translator.translateType(type);
 
-  w.Local addLocal(w.ValueType type) {
-    return b.addLocal(type);
-  }
+  w.Local addLocal(w.ValueType type, {String? name}) =>
+      b.addLocal(type, name: name);
 
   DartType dartTypeOf(Expression exp) {
     if (exp is ConstantExpression) {
@@ -257,7 +256,12 @@ abstract class AstCodeGenerator
         int index,
         Constant? defaultValue,
         bool isRequired) {
-      w.Local local = paramLocals[implicitParams + index];
+      final localIndex = implicitParams + index;
+      w.Local local = paramLocals[localIndex];
+      final variableName = variable.name;
+      if (variableName != null) {
+        b.localNames[local.index] = variableName;
+      }
       if (defaultValue == ParameterInfo.defaultValueSentinel) {
         // The default value for this parameter differs between implementations
         // within the same selector. This means that callers will pass the
@@ -357,7 +361,8 @@ abstract class AstCodeGenerator
       if (local.type == w.RefType.extern(nullable: true) &&
           !(parameterType is InterfaceType &&
               parameterType.classNode == translator.wasmExternRefClass)) {
-        w.Local newLocal = addLocal(translateType(parameterType));
+        w.Local newLocal =
+            addLocal(translateType(parameterType), name: parameter.name);
         b.local_get(local);
         translator.convertType(b, local.type, newLocal.type);
         b.local_set(newLocal);
@@ -490,9 +495,10 @@ abstract class AstCodeGenerator
         member.isInstanceMember || reference.isConstructorBodyReference;
     if (hasThis) {
       thisLocal = paramLocals[0];
+      b.localNames[thisLocal!.index] = "this";
       final preciseThisType = translator.preciseThisFor(member);
       if (translator.needsConversion(thisLocal!.type, preciseThisType)) {
-        preciseThisLocal = addLocal(preciseThisType);
+        preciseThisLocal = addLocal(preciseThisType, name: "preciseThis");
         b.local_get(thisLocal!);
         translator.convertType(b, thisLocal!.type, preciseThisType);
         b.local_set(preciseThisLocal!);
@@ -537,9 +543,10 @@ abstract class AstCodeGenerator
         }
 
         if (context.containsThis) {
-          thisLocal = addLocal(context
-              .struct.fields[context.thisFieldIndex].type.unpacked
-              .withNullability(false));
+          thisLocal = addLocal(
+              context.struct.fields[context.thisFieldIndex].type.unpacked
+                  .withNullability(false),
+              name: "this");
           preciseThisLocal = thisLocal;
 
           b.struct_get(context.struct, context.thisFieldIndex);
@@ -794,7 +801,7 @@ abstract class AstCodeGenerator
     w.Local? local;
     Capture? capture = closures.captures[node];
     if (capture == null || !capture.written) {
-      local = addLocal(type);
+      local = addLocal(type, name: node.name);
       locals[node] = local;
     }
 
@@ -836,7 +843,7 @@ abstract class AstCodeGenerator
     w.Local? local;
     final Capture? capture = closures.captures[node];
     if (capture == null || !capture.written) {
-      local = addLocal(type);
+      local = addLocal(type, name: node.name);
       locals[node] = local;
     }
 
@@ -1352,7 +1359,8 @@ abstract class AstCodeGenerator
         // Since the flow of the return value through the returnValueLocal
         // crosses control-flow constructs, the local needs to always have a
         // defaultable type in order for the Wasm code to validate.
-        returnValueLocal ??= addLocal(returnType.withNullability(true));
+        returnValueLocal ??=
+            addLocal(returnType.withNullability(true), name: "returnValue");
         b.local_set(returnValueLocal!);
       }
       b.br(returnFinalizers.last.label);

pkg/dart2wasm/lib/intrinsics.dart

@@ -1761,7 +1761,8 @@ class Intrinsifier {
         w.ArrayType arrayType =
             (functionType.outputs.single as w.RefType).heapType as w.ArrayType;
         w.Local object = paramLocals[0];
-        w.Local preciseObject = codeGen.addLocal(classInfo.nonNullableType);
+        w.Local preciseObject =
+            codeGen.addLocal(classInfo.nonNullableType, name: "this");
         b.local_get(object);
         b.ref_cast(classInfo.nonNullableType);
         b.local_set(preciseObject);

pkg/dart2wasm/lib/sync_star.dart

@@ -168,13 +168,16 @@ class SyncStarStateMachineCodeGenerator extends StateMachineCodeGenerator {
     Context? localContext = context;
     while (localContext != null) {
       if (!localContext.isEmpty) {
-        localContext.currentLocal =
-            b.addLocal(w.RefType.def(localContext.struct, nullable: true));
+        localContext.currentLocal = b.addLocal(
+            w.RefType.def(localContext.struct, nullable: true),
+            name: "context");
         if (localContext.containsThis) {
           assert(thisLocal == null);
-          thisLocal = b.addLocal(localContext
-              .struct.fields[localContext.thisFieldIndex].type.unpacked
-              .withNullability(false));
+          thisLocal = b.addLocal(
+              localContext
+                  .struct.fields[localContext.thisFieldIndex].type.unpacked
+                  .withNullability(false),
+              name: "this");
           translator
               .getDummyValuesCollectorForModule(b.module)
               .instantiateDummyValue(b, thisLocal!.type);
@@ -187,7 +190,7 @@ class SyncStarStateMachineCodeGenerator extends StateMachineCodeGenerator {
     }
 
     // Read target index from the suspend state.
-    targetIndexLocal = addLocal(w.NumType.i32);
+    targetIndexLocal = addLocal(w.NumType.i32, name: "targetIndex");
     b.local_get(_suspendStateLocal);
     b.struct_get(suspendStateInfo.struct, FieldIndex.suspendStateTargetIndex);
     b.local_set(targetIndexLocal);

pkg/wasm_builder/lib/src/builder/instructions.dart

@@ -171,6 +171,12 @@ class InstructionsBuilder with Builder<ir.Instructions> {
   /// Locals declared in this body, including parameters.
   final List<ir.Local> locals = [];
 
+  /// Names of the locals in `locals`.
+  ///
+  /// Most of the locals won't have names, so this is a [Map] instead of [List]
+  /// like [locals], with local indices as keys and names as values.
+  final Map<int, String> localNames = {};
+
   /// Whether a textual trace of the instruction stream should be recorded when
   /// emitting instructions (provided asserts are enabled).
   ///
@@ -251,8 +257,8 @@ class InstructionsBuilder with Builder<ir.Instructions> {
   }
 
   @override
-  ir.Instructions forceBuild() => ir.Instructions(
-      locals, _instructions, _stackTraces, _traceLines, _sourceMappings);
+  ir.Instructions forceBuild() => ir.Instructions(locals, localNames,
+      _instructions, _stackTraces, _traceLines, _sourceMappings);
 
   void _add(ir.Instruction i) {
     assert(!_constantExpression || i.isConstant,
@@ -271,7 +277,11 @@ class InstructionsBuilder with Builder<ir.Instructions> {
     return local;
   }
 
-  ir.Local addLocal(ir.ValueType type) {
+  ir.Local addLocal(ir.ValueType type, {String? name}) {
+    if (name != null) {
+      final index = locals.length;
+      localNames[index] = name;
+    }
     final local = ir.Local(locals.length, type);
     locals.add(local);
     _localInitialized.add(type.defaultable);

pkg/wasm_builder/lib/src/ir/function.dart

@@ -46,6 +46,8 @@ class DefinedFunction extends BaseFunction implements Serializable {
   /// All local variables defined in the function, including its inputs.
   List<Local> get locals => body.locals;
 
+  Map<int, String> get localNames => body.localNames;
+
   DefinedFunction(
       super.enclosingModule, this.body, super.finalizableIndex, super.type,
       [super.functionName]);

pkg/wasm_builder/lib/src/ir/instructions.dart

@@ -10,6 +10,12 @@ class Instructions implements Serializable {
   /// The locals used by this group of instructions.
   final List<Local> locals;
 
+  /// Names of the locals in `locals`.
+  ///
+  /// Most of the locals won't have names, so this is a [Map] instead of [List]
+  /// like [locals], with local indices as keys and names as values.
+  final Map<int, String> localNames;
+
   /// A sequence of Wasm instructions.
   final List<Instruction> instructions;
 
@@ -27,8 +33,8 @@ class Instructions implements Serializable {
   final List<SourceMapping>? _sourceMappings;
 
   /// Create a new instruction sequence.
-  Instructions(this.locals, this.instructions, this._stackTraces,
-      this._traceLines, this._sourceMappings);
+  Instructions(this.locals, this.localNames, this.instructions,
+      this._stackTraces, this._traceLines, this._sourceMappings);
 
   @override
   void serialize(Serializer s) {

pkg/wasm_builder/lib/src/serialize/sections.dart

@@ -471,6 +471,28 @@ class NameSection extends CustomSection {
       }
     }
 
+    final localNameSubsection = Serializer();
+    List<ir.DefinedFunction> functionsWithLocalNames = [];
+    for (final function in functions) {
+      if (function is ir.DefinedFunction) {
+        if (function.localNames.isNotEmpty) {
+          functionsWithLocalNames.add(function);
+        }
+      }
+    }
+    localNameSubsection.writeUnsigned(functionsWithLocalNames.length);
+
+    if (functionsWithLocalNames.isNotEmpty) {
+      for (final function in functionsWithLocalNames) {
+        localNameSubsection.writeUnsigned(function.finalizableIndex.value);
+        localNameSubsection.writeUnsigned(function.localNames.length);
+        for (final entry in function.localNames.entries) {
+          localNameSubsection.writeUnsigned(entry.key);
+          localNameSubsection.writeName(entry.value);
+        }
+      }
+    }
+
     s.writeByte(0); // Module name subsection
     s.writeUnsigned(moduleNameSubsection.data.length);
     s.writeData(moduleNameSubsection);
@@ -479,6 +501,10 @@ class NameSection extends CustomSection {
     s.writeUnsigned(functionNameSubsection.data.length);
     s.writeData(functionNameSubsection);
 
+    s.writeByte(2); // Local names substion
+    s.writeUnsigned(localNameSubsection.data.length);
+    s.writeData(localNameSubsection);
+
     s.writeByte(4); // Type names subsection
     s.writeUnsigned(typeNameSubsection.data.length);
     s.writeData(typeNameSubsection);