Add code comments to inline cache stubs.

runtime/vm/stub_code_arm.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_ARM)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/cpu.h"
@@ skipping 1231 matching lines @@
 
 
 // Note: R5 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) {
+  __ Comment("Fast Smi op");
   __ ldr(R0, Address(SP, 0 * kWordSize));
   __ ldr(R1, Address(SP, 1 * kWordSize));
   __ orr(TMP, R0, Operand(R1));
   __ tst(TMP, Operand(kSmiTagMask));
   __ b(not_smi_or_overflow, NE);
   switch (kind) {
     case Token::kADD: {
       __ adds(R0, R1, Operand(R0));  // Adds.
       __ b(not_smi_or_overflow, VS);  // Branch if overflow.
       break;
@@ skipping 65 matching lines @@
     ASSERT(ICData::NumArgsTestedShift() == 0);  // No shift needed.
     __ and_(R6, R6, Operand(ICData::NumArgsTestedMask()));
     __ CompareImmediate(R6, num_args);
     __ b(&ok, EQ);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
 
-  // Check single stepping.
+  __ Comment("Check single stepping");
   Label stepping, done_stepping;
   __ LoadIsolate(R6);
   __ ldrb(R6, Address(R6, Isolate::single_step_offset()));
   __ CompareImmediate(R6, 0);
   __ b(&stepping, NE);
   __ 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) {
       __ ldr(R0, Address(SP, 1 * kWordSize));
       __ UpdateRangeFeedback(R0, 0, R5, R1, R4, &not_smi_or_overflow);
     }
 
     __ ldr(R0, Address(SP, 0 * kWordSize));
     __ UpdateRangeFeedback(R0, num_args - 1, R5, R1, R4, &not_smi_or_overflow);
   }
   if (kind != Token::kILLEGAL) {
     EmitFastSmiOp(assembler, kind, num_args, &not_smi_or_overflow);
   }
   __ Bind(&not_smi_or_overflow);
 
+  __ Comment("Extract ICData initial values and receiver cid");
   // Load arguments descriptor into R4.
   __ ldr(R4, FieldAddress(R5, ICData::arguments_descriptor_offset()));
   // Loop that checks if there is an IC data match.
   Label loop, update, test, found;
   // R5: IC data object (preserved).
   __ ldr(R6, FieldAddress(R5, ICData::ic_data_offset()));
   // R6: ic_data_array with check entries: classes and target functions.
   __ AddImmediate(R6, R6, Array::data_offset() - kHeapObjectTag);
   // R6: 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).
   __ ldr(R7, FieldAddress(R4, ArgumentsDescriptor::count_offset()));
   __ sub(R7, R7, Operand(Smi::RawValue(1)));
   __ ldr(R0, Address(SP, R7, LSL, 1));  // R7 (argument_count - 1) is smi.
   __ LoadTaggedClassIdMayBeSmi(R0, R0);
   // R7: argument_count - 1 (smi).
   // R0: receiver's class ID (smi).
   __ ldr(R1, Address(R6, 0));  // First class id (smi) to check.
   __ b(&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.
       __ AddImmediate(R0, R7, Smi::RawValue(-i));
       __ ldr(R0, Address(SP, R0, LSL, 1));
       __ LoadTaggedClassIdMayBeSmi(R0, R0);
       // R0: next argument class ID (smi).
       __ LoadFromOffset(kWord, R1, R6, i * kWordSize);
       // R1: next class ID to check (smi).
@@ skipping 14 matching lines @@
   }
 
   const intptr_t entry_size = ICData::TestEntryLengthFor(num_args) * kWordSize;
   __ AddImmediate(R6, entry_size);  // Next entry.
   __ ldr(R1, Address(R6, 0));  // Next class ID.
 
   __ Bind(&test);
   __ CompareImmediate(R1, Smi::RawValue(kIllegalCid));  // Done?
   __ b(&loop, NE);
 
-  // IC miss.
+  __ Comment("IC miss");
   // Compute address of arguments.
   // R7: argument_count - 1 (smi).
   __ add(R7, SP, Operand(R7, LSL, 1));  // R7 is Smi.
   // R7: address of receiver.
   // Create a stub frame as we are pushing some objects on the stack before
   // calling into the runtime.
   __ EnterStubFrame();
   __ LoadImmediate(R0, reinterpret_cast<intptr_t>(Object::null()));
   // Preserve IC data object and arguments descriptor array and
   // setup space on stack for result (target code object).
@@ skipping 14 matching lines @@
   __ LeaveStubFrame();
   Label call_target_function;
   __ b(&call_target_function);
 
   __ Bind(&found);
   // R6: 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;
   __ LoadFromOffset(kWord, R0, R6, target_offset);
 
-  // Update counter.
+  __ Comment("Update caller's counter");
   __ LoadFromOffset(kWord, R1, R6, count_offset);
   __ adds(R1, R1, Operand(Smi::RawValue(1)));
   __ LoadImmediate(R1, Smi::RawValue(Smi::kMaxValue), VS);  // Overflow.
   __ StoreIntoSmiField(Address(R6, count_offset), R1);
 
+  __ Comment("Call target");
   __ Bind(&call_target_function);
   // R0: target function.
   __ ldr(R2, FieldAddress(R0, Function::instructions_offset()));
   __ AddImmediate(R2, Instructions::HeaderSize() - kHeapObjectTag);
   if (range_collection_mode == kCollectRanges) {
     __ ldr(R1, Address(SP, 0 * kWordSize));
     if (num_args == 2) {
       __ ldr(R3, Address(SP, 1 * kWordSize));
     }
     __ EnterStubFrame();
@@ skipping 575 matching lines @@
   const Register right = R0;
   __ ldr(left, Address(SP, 1 * kWordSize));
   __ ldr(right, Address(SP, 0 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ Ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM