Add code comments to inline cache stubs.

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 1188 matching lines @@
 
 // Note: RBX must be preserved.
 // Attempt a quick Smi operation for known operations ('kind'). The ICData
 // must have been primed with a Smi/Smi check that will be used for counting
 // the invocations.
 static void EmitFastSmiOp(Assembler* assembler,
                           Token::Kind kind,
                           intptr_t num_args,
                           Label* not_smi_or_overflow,
                           bool should_update_result_range) {
+  __ Comment("Fast Smi op");
   if (FLAG_throw_on_javascript_int_overflow) {
     // The overflow check is more complex than implemented below.
     return;
   }
   ASSERT(num_args == 2);
   __ movq(RCX, Address(RSP, + 1 * kWordSize));  // Right
   __ movq(RAX, Address(RSP, + 2 * kWordSize));  // Left.
   __ movq(R12, RCX);
   __ orq(R12, RAX);
   __ testq(R12, Immediate(kSmiTagMask));
@@ skipping 86 matching lines @@
     __ movl(RCX, FieldAddress(RBX, ICData::state_bits_offset()));
     ASSERT(ICData::NumArgsTestedShift() == 0);  // No shift needed.
     __ andq(RCX, Immediate(ICData::NumArgsTestedMask()));
     __ cmpq(RCX, Immediate(num_args));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
-  // Check single stepping.
+  __ Comment("Check single stepping");
   Label stepping, done_stepping;
   __ LoadIsolate(RAX);
   __ cmpb(Address(RAX, Isolate::single_step_offset()), Immediate(0));
   __ j(NOT_EQUAL, &stepping);
   __ Bind(&done_stepping);
 
+  __ Comment("Range feedback collection");
   Label not_smi_or_overflow;
   if (range_collection_mode == kCollectRanges) {
     ASSERT((num_args == 1) || (num_args == 2));
     if (num_args == 2) {
       __ movq(RAX, Address(RSP, + 2 * kWordSize));
       __ UpdateRangeFeedback(RAX, 0, RBX, RCX, &not_smi_or_overflow);
     }
 
     __ movq(RAX, Address(RSP, + 1 * kWordSize));
     __ UpdateRangeFeedback(RAX, (num_args - 1), RBX, RCX, &not_smi_or_overflow);
   }
   if (kind != Token::kILLEGAL) {
     EmitFastSmiOp(
         assembler,
         kind,
         num_args,
         &not_smi_or_overflow,
         range_collection_mode == kCollectRanges);
   }
   __ Bind(&not_smi_or_overflow);
 
+  __ Comment("Extract ICData initial values and receiver cid");
   // Load arguments descriptor into R10.
   __ movq(R10, FieldAddress(RBX, ICData::arguments_descriptor_offset()));
   // Loop that checks if there is an IC data match.
   Label loop, update, test, found;
   // RBX: IC data object (preserved).
   __ movq(R12, FieldAddress(RBX, ICData::ic_data_offset()));
   // R12: ic_data_array with check entries: classes and target functions.
   __ leaq(R12, FieldAddress(R12, Array::data_offset()));
   // R12: points directly to the first ic data array element.
 
   // Get the receiver's class ID (first read number of arguments from
   // arguments descriptor array and then access the receiver from the stack).
   __ movq(RAX, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
   __ movq(R13, Address(RSP, RAX, TIMES_4, 0));  // RAX (argument count) is Smi.
   __ LoadTaggedClassIdMayBeSmi(RAX, R13);
   // RAX: receiver's class ID as smi.
   __ movq(R13, Address(R12, 0));  // First class ID (Smi) to check.
   __ jmp(&test);
 
+  __ Comment("ICData loop");
   __ Bind(&loop);
   for (int i = 0; i < num_args; i++) {
     if (i > 0) {
       // If not the first, load the next argument's class ID.
       __ movq(RAX, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
       __ movq(R13, Address(RSP, RAX, TIMES_4, - i * kWordSize));
       __ LoadTaggedClassIdMayBeSmi(RAX, R13);
       // RAX: next argument class ID (smi).
       __ movq(R13, Address(R12, i * kWordSize));
       // R13: next class ID to check (smi).
@@ skipping 15 matching lines @@
   }
 
   const intptr_t entry_size = ICData::TestEntryLengthFor(num_args) * kWordSize;
   __ addq(R12, Immediate(entry_size));  // Next entry.
   __ movq(R13, Address(R12, 0));  // Next class ID.
 
   __ Bind(&test);
   __ cmpq(R13, Immediate(Smi::RawValue(kIllegalCid)));  // Done?
   __ j(NOT_EQUAL, &loop, Assembler::kNearJump);
 
-  // IC miss.
+  __ Comment("IC miss");
   __ LoadObject(R12, Object::null_object(), PP);
   // Compute address of arguments (first read number of arguments from
   // arguments descriptor array and then compute address on the stack).
   __ movq(RAX, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
   __ leaq(RAX, Address(RSP, RAX, TIMES_4, 0));  // RAX is Smi.
   __ EnterStubFrame();
   __ pushq(R10);  // Preserve arguments descriptor array.
   __ pushq(RBX);  // Preserve IC data object.
   __ pushq(R12);  // Setup space on stack for result (target code object).
   // Push call arguments.
   for (intptr_t i = 0; i < num_args; i++) {
     __ movq(RCX, Address(RAX, -kWordSize * i));
     __ pushq(RCX);
   }
   __ pushq(RBX);  // Pass IC data object.
   __ CallRuntime(handle_ic_miss, num_args + 1);
   // Remove the call arguments pushed earlier, including the IC data object.
   for (intptr_t i = 0; i < num_args + 1; i++) {
     __ popq(RAX);
   }
   __ popq(RAX);  // Pop returned function object into RAX.
   __ popq(RBX);  // Restore IC data array.
   __ popq(R10);  // Restore arguments descriptor array.
   __ LeaveStubFrame();
   Label call_target_function;
   __ jmp(&call_target_function);
 
   __ Bind(&found);
+  __ Comment("Update caller's counter");
   // R12: Pointer to an IC data check group.
   const intptr_t target_offset = ICData::TargetIndexFor(num_args) * kWordSize;
   const intptr_t count_offset = ICData::CountIndexFor(num_args) * kWordSize;
   __ movq(RAX, Address(R12, target_offset));
 
   // Update counter.
   __ movq(R8, Address(R12, count_offset));
   __ addq(R8, Immediate(Smi::RawValue(1)));
   __ movq(R9, Immediate(Smi::RawValue(Smi::kMaxValue)));
   __ cmovnoq(R9, R8);
   __ StoreIntoSmiField(Address(R12, count_offset), R9);
 
+  __ Comment("Call target");
   __ Bind(&call_target_function);
   // RAX: Target function.
   Label is_compiled;
   __ movq(RCX, FieldAddress(RAX, Function::instructions_offset()));
   __ addq(RCX, Immediate(Instructions::HeaderSize() - kHeapObjectTag));
   if (range_collection_mode == kCollectRanges) {
     __ movq(R8, Address(RSP, + 1 * kWordSize));
     if (num_args == 2) {
       __ movq(R9, Address(RSP, + 2 * kWordSize));
     }
@@ skipping 614 matching lines @@
 
   __ movq(left, Address(RSP, 2 * kWordSize));
   __ movq(right, Address(RSP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64