[interpreter] Add support for scalable operands.

src/runtime/runtime-interpreter.cc

Index: src/runtime/runtime-interpreter.cc
diff --git a/src/runtime/runtime-interpreter.cc b/src/runtime/runtime-interpreter.cc
index 9c53317b4af7cbeec67a3634b96555f4ed803f0f..f593235d20318fc1d899ca4ec887a348367b07b3 100644
--- a/src/runtime/runtime-interpreter.cc
+++ b/src/runtime/runtime-interpreter.cc
@@ -28,8 +28,30 @@ RUNTIME_FUNCTION(Runtime_InterpreterNewClosure) {
 
 namespace {
 
+void AdvanceToOffsetForTracing(
+    interpreter::BytecodeArrayIterator& bytecode_iterator, int offset) {
+  if (offset > 0) {
+    uint8_t last_byte = bytecode_iterator.bytecode_array()->get(offset - 1);
+    auto maybe_bytecode = static_cast<interpreter::Bytecode>(last_byte);
+    if (interpreter::Bytecodes::IsPrefixScalingBytecode(maybe_bytecode)) {
+      // Previous byte looks like a prefix byte so scan forward slowly.
+      while (bytecode_iterator.current_offset() +
+                 bytecode_iterator.current_bytecode_size() <=
+             offset) {
+        bytecode_iterator.Advance();
+      }
+      DCHECK(bytecode_iterator.current_offset() == offset ||
+             ((bytecode_iterator.current_offset() == offset - 1) &&
+              bytecode_iterator.current_operand_scale() > 1));
+    } else {
+      bytecode_iterator.set_current_offset(offset);
+    }
+  }
+  DCHECK(bytecode_iterator.current_bytecode() != interpreter::Bytecode::kWide);
+}
+
 void PrintRegisters(std::ostream& os, bool is_input,
-                    Handle<BytecodeArray> bytecode_array, int bytecode_offset,
+                    interpreter::BytecodeArrayIterator& bytecode_iterator,
                     Handle<Object> accumulator) {
   static const int kRegFieldWidth = static_cast<int>(strlen("accumulator"));
   static const char* kInputColourCode = "\033[0;36m";
@@ -46,15 +68,13 @@ void PrintRegisters(std::ostream& os, bool is_input,
   os << " ]" << std::endl;
 
   // Find the location of the register file.
-  JavaScriptFrameIterator frame_iterator(bytecode_array->GetIsolate());
+  JavaScriptFrameIterator frame_iterator(
+      bytecode_iterator.bytecode_array()->GetIsolate());
   JavaScriptFrame* frame = frame_iterator.frame();
   Address register_file =
       frame->fp() + InterpreterFrameConstants::kRegisterFilePointerFromFp;
 
   // Print the registers.
-  interpreter::BytecodeArrayIterator bytecode_iterator(bytecode_array);
-  bytecode_iterator.set_current_offset(
-      bytecode_offset - BytecodeArray::kHeaderSize + kHeapObjectTag);
   interpreter::Bytecode bytecode = bytecode_iterator.current_bytecode();
   int operand_count = interpreter::Bytecodes::NumberOfOperands(bytecode);
   for (int operand_index = 0; operand_index < operand_count; operand_index++) {
@@ -74,7 +94,7 @@ void PrintRegisters(std::ostream& os, bool is_input,
         Object* reg_object = Memory::Object_at(reg_location);
         os << "      [ " << std::setw(kRegFieldWidth)
            << interpreter::Register(reg_index).ToString(
-                  bytecode_array->parameter_count())
+                  bytecode_iterator.bytecode_array()->parameter_count())
            << kArrowDirection;
         reg_object->ShortPrint(os);
         os << " ]" << std::endl;
@@ -96,20 +116,24 @@ RUNTIME_FUNCTION(Runtime_InterpreterTraceBytecodeEntry) {
   CONVERT_ARG_HANDLE_CHECKED(Object, accumulator, 2);
   OFStream os(stdout);
 
-  // Print bytecode.
-  const uint8_t* bytecode_address =
-      reinterpret_cast<const uint8_t*>(*bytecode_array) + bytecode_offset;
-  Vector<char> buf = Vector<char>::New(50);
-  SNPrintF(buf, "%p", bytecode_address);
-  os << " -> " << buf.start() << " (" << bytecode_offset << ") : ";
-  interpreter::Bytecodes::Decode(os, bytecode_address,
-                                 bytecode_array->parameter_count());
-  os << std::endl;
-
-  // Print all input registers and accumulator.
-  PrintRegisters(os, true, bytecode_array, bytecode_offset, accumulator);
-
-  os << std::flush;
+  int offset = bytecode_offset - BytecodeArray::kHeaderSize + kHeapObjectTag;
+  interpreter::BytecodeArrayIterator bytecode_iterator(bytecode_array);
+  AdvanceToOffsetForTracing(bytecode_iterator, offset);
+  if (offset == bytecode_iterator.current_offset()) {
+    // Print bytecode.
+    const uint8_t* bytecode_address =
+        reinterpret_cast<const uint8_t*>(*bytecode_array) + bytecode_offset;
+    Vector<char> buf = Vector<char>::New(50);
+    SNPrintF(buf, "%p", bytecode_address);
+    os << " -> " << buf.start() << " (" << bytecode_offset << ") : ";
+    interpreter::Bytecodes::Decode(os, bytecode_address,
+                                   bytecode_array->parameter_count());
+    os << std::endl;
+    // Print all input registers and accumulator.
+    PrintRegisters(os, true, bytecode_iterator, accumulator);
+
+    os << std::flush;
+  }
   return isolate->heap()->undefined_value();
 }
 
@@ -119,11 +143,17 @@ RUNTIME_FUNCTION(Runtime_InterpreterTraceBytecodeExit) {
   CONVERT_ARG_HANDLE_CHECKED(BytecodeArray, bytecode_array, 0);
   CONVERT_SMI_ARG_CHECKED(bytecode_offset, 1);
   CONVERT_ARG_HANDLE_CHECKED(Object, accumulator, 2);
-  OFStream os(stdout);
 
-  // Print all output registers and accumulator.
-  PrintRegisters(os, false, bytecode_array, bytecode_offset, accumulator);
-  os << std::flush;
+  int offset = bytecode_offset - BytecodeArray::kHeaderSize + kHeapObjectTag;
+  interpreter::BytecodeArrayIterator bytecode_iterator(bytecode_array);
+  AdvanceToOffsetForTracing(bytecode_iterator, offset);
+  if (bytecode_iterator.current_operand_scale() == 1 ||
+      offset > bytecode_iterator.current_offset()) {
+    OFStream os(stdout);
+    // Print all output registers and accumulator.
+    PrintRegisters(os, false, bytecode_iterator, accumulator);
+    os << std::flush;
+  }
   return isolate->heap()->undefined_value();
 }