[wasm_builder] Fix --watch option to work with instructions

The `--watch` debug option to print the stack trace leading to a
particular byte in the output Wasm file didn't work for instructions
after the instruction encoder was changed to produce intermediate
instruction objects.

This is fixed by keeping a map from instruction objects to stack
traces in the instructions builder and registering those stack traces
when serializing the instructions.

Change-Id: I90d665753813452d07783c7f47e1e6bf63a3a18e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/324681
Reviewed-by: Jess Lally <[email protected]>
Commit-Queue: Aske Simon Christensen <[email protected]>

Author: askeksa

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

@@ -144,9 +144,13 @@ class InstructionsBuilder with Builder<ir.Instructions> {
   /// List of instructions.
   final List<ir.Instruction> _instructions = [];
 
+  /// Stored stack traces leading to the instructions for watch points.
+  final Map<ir.Instruction, StackTrace>? _stackTraces;
+
   /// Create a new instruction sequence.
   InstructionsBuilder(this.module, List<ir.ValueType> outputs,
-      {this.isGlobalInitializer = false}) {
+      {this.isGlobalInitializer = false})
+      : _stackTraces = module.watchPoints != null ? {} : null {
     _labelStack.add(Expression(const [], outputs));
   }
 
@@ -161,9 +165,14 @@ class InstructionsBuilder with Builder<ir.Instructions> {
 
   @override
   ir.Instructions forceBuild() =>
-      ir.Instructions(locals, _instructions, _traceLines);
+      ir.Instructions(locals, _instructions, _stackTraces, _traceLines);
 
-  void _add(ir.Instruction i) => _instructions.add(i);
+  void _add(ir.Instruction i) {
+    _instructions.add(i);
+    if (module.watchPoints != null) {
+      _stackTraces![i] = StackTrace.current;
+    }
+  }
 
   ir.Local addLocal(ir.ValueType type, {required bool isParameter}) {
     final local = ir.Local(locals.length, type);

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

@@ -14,17 +14,21 @@ class Instructions implements Serializable {
   /// A sequence of Wasm instructions.
   final List<Instruction> instructions;
 
+  final Map<Instruction, StackTrace>? _stackTraces;
+
   final List<String> _traceLines;
 
   /// A string trace.
   late final trace = _traceLines.join();
 
   /// Create a new instruction sequence.
-  Instructions(this.locals, this.instructions, this._traceLines);
+  Instructions(
+      this.locals, this.instructions, this._stackTraces, this._traceLines);
 
   @override
   void serialize(Serializer s) {
     for (final i in instructions) {
+      if (_stackTraces != null) s.debugTrace(_stackTraces![i]!);
       i.serialize(s);
     }
   }

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

@@ -34,19 +34,19 @@ class Serializer {
     }
   }
 
-  void _debugTrace(Object data) {
+  void debugTrace(Object data) {
     _traces[_index] ??= data;
   }
 
   void writeByte(int byte) {
-    if (traceEnabled) _debugTrace(StackTrace.current);
+    if (traceEnabled) debugTrace(StackTrace.current);
     assert(byte == byte & 0xFF);
     _ensure(1);
     _data[_index++] = byte;
   }
 
   void writeBytes(List<int> bytes) {
-    if (traceEnabled) _debugTrace(StackTrace.current);
+    if (traceEnabled) debugTrace(StackTrace.current);
     _ensure(bytes.length);
     _data.setRange(_index, _index += bytes.length, bytes);
   }
@@ -102,7 +102,7 @@ class Serializer {
   }
 
   void writeData(Serializer chunk, [List<int>? watchPoints]) {
-    if (traceEnabled) _debugTrace(chunk);
+    if (traceEnabled) debugTrace(chunk);
     if (watchPoints != null) {
       for (int watchPoint in watchPoints) {
         if (_index <= watchPoint && watchPoint < _index + chunk.data.length) {