Implement optional parameter handling in ARM vm.

runtime/vm/flow_graph_compiler_arm.cc

Index: runtime/vm/flow_graph_compiler_arm.cc
===================================================================
--- runtime/vm/flow_graph_compiler_arm.cc	(revision 20365)
+++ runtime/vm/flow_graph_compiler_arm.cc	(working copy)
@@ -167,7 +167,228 @@
 
 
 void FlowGraphCompiler::CopyParameters() {
-  UNIMPLEMENTED();
+  __ Comment("Copy parameters");

[zra, 2013/03/22 16:45:10]

Maybe add a comment explaining register contents on entry since R5 is used for
something other than ic data below.

[regis, 2013/03/22 17:26:11]

Added comment here and in FlowGraphCompiler::CompileGraph().
R5 is free to be used. It is reloaded with ic-data if needed. Same code as on
IA32 and X64.

+  const Function& function = parsed_function().function();
+  LocalScope* scope = parsed_function().node_sequence()->scope();
+  const int num_fixed_params = function.num_fixed_parameters();
+  const int num_opt_pos_params = function.NumOptionalPositionalParameters();
+  const int num_opt_named_params = function.NumOptionalNamedParameters();
+  const int num_params =
+      num_fixed_params + num_opt_pos_params + num_opt_named_params;
+  ASSERT(function.NumParameters() == num_params);
+  ASSERT(parsed_function().first_parameter_index() == kFirstLocalSlotIndex);
+
+  // Check that min_num_pos_args <= num_pos_args <= max_num_pos_args,
+  // where num_pos_args is the number of positional arguments passed in.
+  const int min_num_pos_args = num_fixed_params;
+  const int max_num_pos_args = num_fixed_params + num_opt_pos_params;
+
+  __ ldr(R8, FieldAddress(R4, ArgumentsDescriptor::positional_count_offset()));
+  // Check that min_num_pos_args <= num_pos_args.
+  Label wrong_num_arguments;
+  __ CompareImmediate(R8, Smi::RawValue(min_num_pos_args));
+  __ b(&wrong_num_arguments, LT);
+  // Check that num_pos_args <= max_num_pos_args.
+  __ CompareImmediate(R8, Smi::RawValue(max_num_pos_args));
+  __ b(&wrong_num_arguments, GT);
+
+  // Copy positional arguments.
+  // Argument i passed at fp[kLastParamSlotIndex + num_args - 1 - i] is copied
+  // to fp[kFirstLocalSlotIndex - i].
+
+  __ ldr(R7, FieldAddress(R4, ArgumentsDescriptor::count_offset()));
+  // Since R7 and R8 are Smi, use LSL 1 instead of LSL 2.
+  // Let R7 point to the last passed positional argument, i.e. to
+  // fp[kLastParamSlotIndex + num_args - 1 - (num_pos_args - 1)].
+  __ sub(R7, R7, ShifterOperand(R8));
+  __ add(R7, FP, ShifterOperand(R7, LSL, 1));
+  __ add(R7, R7, ShifterOperand(kLastParamSlotIndex * kWordSize));
+
+  // Let R6 point to the last copied positional argument, i.e. to
+  // fp[kFirstLocalSlotIndex - (num_pos_args - 1)].
+  __ AddImmediate(R6, FP, (kFirstLocalSlotIndex + 1) * kWordSize);
+  __ sub(R6, R6, ShifterOperand(R8, LSL, 1));  // R8 is a Smi.
+  __ SmiUntag(R8);
+  Label loop, loop_condition;
+  __ b(&loop_condition);
+  // We do not use the final allocation index of the variable here, i.e.
+  // scope->VariableAt(i)->index(), because captured variables still need
+  // to be copied to the context that is not yet allocated.
+  const Address argument_addr(R7, R8, LSL, 2);
+  const Address copy_addr(R6, R8, LSL, 2);
+  __ Bind(&loop);
+  __ ldr(IP, argument_addr);
+  __ str(IP, copy_addr);
+  __ Bind(&loop_condition);
+  __ subs(R8, R8, ShifterOperand(1));
+  __ b(&loop, PL);
+
+  // Copy or initialize optional named arguments.
+  Label all_arguments_processed;
+  if (num_opt_named_params > 0) {
+    // Start by alphabetically sorting the names of the optional parameters.
+    LocalVariable** opt_param = new LocalVariable*[num_opt_named_params];
+    int* opt_param_position = new int[num_opt_named_params];
+    for (int pos = num_fixed_params; pos < num_params; pos++) {
+      LocalVariable* parameter = scope->VariableAt(pos);
+      const String& opt_param_name = parameter->name();
+      int i = pos - num_fixed_params;
+      while (--i >= 0) {
+        LocalVariable* param_i = opt_param[i];
+        const intptr_t result = opt_param_name.CompareTo(param_i->name());
+        ASSERT(result != 0);
+        if (result > 0) break;
+        opt_param[i + 1] = opt_param[i];
+        opt_param_position[i + 1] = opt_param_position[i];
+      }
+      opt_param[i + 1] = parameter;
+      opt_param_position[i + 1] = pos;
+    }
+    // Generate code handling each optional parameter in alphabetical order.
+    __ ldr(R7, FieldAddress(R4, ArgumentsDescriptor::count_offset()));
+    __ ldr(R8,
+           FieldAddress(R4, ArgumentsDescriptor::positional_count_offset()));
+    __ SmiUntag(R8);
+    // Let R7 point to the first passed argument, i.e. to fp[1 + argc - 0].

[zra, 2013/03/22 16:45:10]

Is this comment outdated?

[regis, 2013/03/22 17:26:11]

Yes. I forgot to remove the old version. The newer version is below.

+    // Let R7 point to the first passed argument, i.e. to
+    // fp[kLastParamSlotIndex + num_args - 1 - 0]; num_args (R7) is Smi.
+    __ add(R7, FP, ShifterOperand(R7, LSL, 1));
+    __ AddImmediate(R7, R7, (kLastParamSlotIndex - 1) * kWordSize);
+    // Let R6 point to the entry of the first named argument.
+    __ add(R6, R4, ShifterOperand(
+        ArgumentsDescriptor::first_named_entry_offset() - kHeapObjectTag));
+    for (int i = 0; i < num_opt_named_params; i++) {
+      Label load_default_value, assign_optional_parameter, next_parameter;
+      const int param_pos = opt_param_position[i];
+      // Check if this named parameter was passed in.
+      // Load R5 with the name of the argument.
+      __ ldr(R5, Address(R6, ArgumentsDescriptor::name_offset()));
+      ASSERT(opt_param[i]->name().IsSymbol());
+      __ CompareObject(R5, opt_param[i]->name());
+      __ b(&load_default_value, NE);
+      // Load R5 with passed-in argument at provided arg_pos, i.e. at
+      // fp[kLastParamSlotIndex + num_args - 1 - arg_pos].
+      __ ldr(R5, Address(R6, ArgumentsDescriptor::position_offset()));
+      // R5 is arg_pos as Smi.
+      // Point to next named entry.
+      __ add(R6, R6, ShifterOperand(ArgumentsDescriptor::named_entry_size()));
+      __ rsb(R5, R5, ShifterOperand(0));
+      Address argument_addr(R7, R5, LSL, 1);  // R5 is a negative Smi.
+      __ ldr(R5, argument_addr);
+      __ b(&assign_optional_parameter);
+      __ Bind(&load_default_value);
+      // Load R5 with default argument.
+      const Object& value = Object::ZoneHandle(
+          parsed_function().default_parameter_values().At(
+              param_pos - num_fixed_params));
+      __ LoadObject(R5, value);
+      __ Bind(&assign_optional_parameter);
+      // Assign R5 to fp[kFirstLocalSlotIndex - param_pos].
+      // We do not use the final allocation index of the variable here, i.e.
+      // scope->VariableAt(i)->index(), because captured variables still need
+      // to be copied to the context that is not yet allocated.
+      const intptr_t computed_param_pos = kFirstLocalSlotIndex - param_pos;
+      const Address param_addr(FP, computed_param_pos * kWordSize);
+      __ str(R5, param_addr);
+      __ Bind(&next_parameter);

[zra, 2013/03/22 16:45:10]

Does anything branch to here?

[regis, 2013/03/22 17:26:11]

Good catch. This is left over code from a previous version supporting optional
parameters with different semantics. Removed here and in the ia32 and x64
versions.

+    }
+    delete[] opt_param;
+    delete[] opt_param_position;
+    // Check that R6 now points to the null terminator in the array descriptor.
+    __ ldr(R5, Address(R6, 0));
+    __ CompareImmediate(R5, reinterpret_cast<int32_t>(Object::null()));
+    __ b(&all_arguments_processed, EQ);
+  } else {
+    ASSERT(num_opt_pos_params > 0);
+    __ ldr(R8,
+           FieldAddress(R4, ArgumentsDescriptor::positional_count_offset()));
+    __ SmiUntag(R8);
+    for (int i = 0; i < num_opt_pos_params; i++) {
+      Label next_parameter;
+      // Handle this optional positional parameter only if k or fewer positional
+      // arguments have been passed, where k is param_pos, the position of this
+      // optional parameter in the formal parameter list.
+      const int param_pos = num_fixed_params + i;
+      __ CompareImmediate(R8, param_pos);
+      __ b(&next_parameter, GT);
+      // Load R5 with default argument.
+      const Object& value = Object::ZoneHandle(
+          parsed_function().default_parameter_values().At(i));
+      __ LoadObject(R5, value);
+      // Assign R5 to fp[kFirstLocalSlotIndex - param_pos].
+      // We do not use the final allocation index of the variable here, i.e.
+      // scope->VariableAt(i)->index(), because captured variables still need
+      // to be copied to the context that is not yet allocated.
+      const intptr_t computed_param_pos = kFirstLocalSlotIndex - param_pos;
+      const Address param_addr(FP, computed_param_pos * kWordSize);
+      __ str(R5, param_addr);
+      __ Bind(&next_parameter);
+    }
+    __ ldr(R7, FieldAddress(R4, ArgumentsDescriptor::count_offset()));
+    __ SmiUntag(R7);
+    // Check that R8 equals R7, i.e. no named arguments passed.
+    __ cmp(R8, ShifterOperand(R7));
+    __ b(&all_arguments_processed, EQ);
+  }
+
+  __ Bind(&wrong_num_arguments);
+  if (StackSize() != 0) {
+    // We need to unwind the space we reserved for locals and copied parameters.
+    // The NoSuchMethodFunction stub does not expect to see that area on the
+    // stack.
+    __ AddImmediate(SP, StackSize() * kWordSize);
+  }
+  // The call below has an empty stackmap because we have just
+  // dropped the spill slots.
+  BitmapBuilder* empty_stack_bitmap = new BitmapBuilder();
+
+  // Invoke noSuchMethod function passing the original name of the function.
+  // If the function is a closure function, use "call" as the original name.
+  const String& name = String::Handle(
+      function.IsClosureFunction() ? Symbols::Call().raw() : function.name());
+  const int kNumArgsChecked = 1;
+  const ICData& ic_data = ICData::ZoneHandle(
+      ICData::New(function, name, Isolate::kNoDeoptId, kNumArgsChecked));
+  __ LoadObject(R5, ic_data);
+  // FP - 4 : saved PP, object pool pointer of caller.
+  // FP + 0 : previous frame pointer.
+  // FP + 4 : return address.
+  // FP + 8 : PC marker, for easy identification of RawInstruction obj.
+  // FP + 12: last argument (arg n-1).
+  // SP + 0 : saved PP.
+  // SP + 16 + 4*(n-1) : first argument (arg 0).
+  // R5 : ic-data.
+  // R4 : arguments descriptor array.
+  __ BranchLink(&StubCode::CallNoSuchMethodFunctionLabel());
+  if (is_optimizing()) {
+    stackmap_table_builder_->AddEntry(assembler()->CodeSize(),
+                                      empty_stack_bitmap,
+                                      0);  // No registers.
+  }
+  // The noSuchMethod call may return.
+  __ LeaveDartFrame();
+  __ Ret();
+
+  __ Bind(&all_arguments_processed);
+  // Nullify originally passed arguments only after they have been copied and
+  // checked, otherwise noSuchMethod would not see their original values.
+  // This step can be skipped in case we decide that formal parameters are
+  // implicitly final, since garbage collecting the unmodified value is not
+  // an issue anymore.
+
+  // R4 : arguments descriptor array.
+  __ ldr(R8, FieldAddress(R4, ArgumentsDescriptor::count_offset()));
+  __ SmiUntag(R8);
+  __ add(R7, FP, ShifterOperand(kLastParamSlotIndex * kWordSize));
+  const Address original_argument_addr(R7, R8, LSL, 2);
+  __ LoadImmediate(IP, reinterpret_cast<intptr_t>(Object::null()));
+  Label null_args_loop, null_args_loop_condition;
+  __ b(&null_args_loop_condition);
+  __ Bind(&null_args_loop);
+  __ str(IP, original_argument_addr);
+  __ Bind(&null_args_loop_condition);
+  __ subs(R8, R8, ShifterOperand(1));
+  __ b(&null_args_loop, PL);
 }
 
 
@@ -435,7 +656,14 @@
                                          intptr_t deopt_id,
                                          intptr_t token_pos,
                                          LocationSummary* locs) {
-  UNIMPLEMENTED();
+  __ LoadObject(R5, ic_data);
+  __ LoadObject(R4, arguments_descriptor);
+  GenerateDartCall(deopt_id,
+                   token_pos,
+                   target_label,
+                   PcDescriptors::kIcCall,
+                   locs);
+  __ Drop(argument_count);
 }