Add code comments to inline cache stubs.

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, 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_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 1261 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,
                           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;
   }
   __ ldr(R0, Address(SP, + 0 * kWordSize));  // Right.
   __ ldr(R1, Address(SP, + 1 * kWordSize));  // Left.
   __ orr(TMP, R0, Operand(R1));
   __ tsti(TMP, Immediate(kSmiTagMask));
   __ b(not_smi_or_overflow, NE);
   switch (kind) {
@@ skipping 79 matching lines @@
                       kNoPP, kUnsignedWord);
     ASSERT(ICData::NumArgsTestedShift() == 0);  // No shift needed.
     __ andi(R6, R6, Immediate(ICData::NumArgsTestedMask()));
     __ CompareImmediate(R6, num_args, kNoPP);
     __ 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, kNoPP);
   __ LoadFromOffset(
       R6, R6, Isolate::single_step_offset(), kNoPP, kUnsignedByte);
   __ CompareRegisters(R6, ZR);
   __ 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,
                   (range_collection_mode == kCollectRanges));
   }
   __ Bind(&not_smi_or_overflow);
 
+  __ Comment("Extract ICData initial values and receiver cid");
   // Load arguments descriptor into R4.
   __ LoadFieldFromOffset(R4, R5, ICData::arguments_descriptor_offset(), kNoPP);
   // Loop that checks if there is an IC data match.
   Label loop, update, test, found;
   // R5: IC data object (preserved).
   __ LoadFieldFromOffset(R6, R5, ICData::ic_data_offset(), kNoPP);
   // R6: ic_data_array with check entries: classes and target functions.
   __ AddImmediate(R6, R6, Array::data_offset() - kHeapObjectTag, kNoPP);
   // 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).
   __ LoadFieldFromOffset(R7, R4, ArgumentsDescriptor::count_offset(), kNoPP);
   __ SmiUntag(R7);  // Untag so we can use the LSL 3 addressing mode.
   __ sub(R7, R7, Operand(1));
 
   // R0 <- [SP + (R7 << 3)]
   __ ldr(R0, Address(SP, R7, UXTX, Address::Scaled));
   __ LoadTaggedClassIdMayBeSmi(R0, R0);
 
   // R7: argument_count - 1 (untagged).
   // R0: receiver's class ID (smi).
   __ ldr(R1, Address(R6));  // 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, -i, kNoPP);
       // R0 <- [SP + (R0 << 3)]
       __ ldr(R0, Address(SP, R0, UXTX, Address::Scaled));
       __ LoadTaggedClassIdMayBeSmi(R0, R0);
       // R0: next argument class ID (smi).
       __ LoadFromOffset(R1, R6, i * kWordSize, kNoPP);
@@ skipping 15 matching lines @@
   }
 
   const intptr_t entry_size = ICData::TestEntryLengthFor(num_args) * kWordSize;
   __ AddImmediate(R6, R6, entry_size, kNoPP);  // Next entry.
   __ ldr(R1, Address(R6));  // Next class ID.
 
   __ Bind(&test);
   __ CompareImmediate(R1, Smi::RawValue(kIllegalCid), kNoPP);  // Done?
   __ b(&loop, NE);
 
-  // IC miss.
+  __ Comment("IC miss");
   // Compute address of arguments.
   // R7: argument_count - 1 (untagged).
   // R7 <- SP + (R7 << 3)
   __ add(R7, SP, Operand(R7, UXTX, 3));  // R7 is Untagged.
   // R7: address of receiver.
   // Create a stub frame as we are pushing some objects on the stack before
   // calling into the runtime.
   __ EnterStubFrame();
   // Preserve IC data object and arguments descriptor array and
   // setup space on stack for result (target code object).
@@ skipping 14 matching lines @@
   // Pop returned function object into R0.
   // Restore arguments descriptor array and IC data array.
   __ Pop(R0);  // Pop returned function object into R0.
   __ Pop(R5);  // Restore IC Data.
   __ Pop(R4);  // Restore arguments descriptor array.
   __ LeaveStubFrame();
   Label call_target_function;
   __ b(&call_target_function);
 
   __ Bind(&found);
+  __ Comment("Update caller's counter");
   // 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(R0, R6, target_offset, kNoPP);
 
   // Update counter.
   __ LoadFromOffset(R1, R6, count_offset, kNoPP);
   __ adds(R1, R1, Operand(Smi::RawValue(1)));
   __ LoadImmediate(R2, Smi::RawValue(Smi::kMaxValue), kNoPP);
   __ csel(R1, R2, R1, VS);  // Overflow.
   __ StoreToOffset(R1, R6, count_offset, kNoPP);
 
+  __ Comment("Call target");
   __ Bind(&call_target_function);
   // R0: target function.
   __ LoadFieldFromOffset(R2, R0, Function::instructions_offset(), kNoPP);
   __ AddImmediate(
       R2, R2, Instructions::HeaderSize() - kHeapObjectTag, kNoPP);
   if (range_collection_mode == kCollectRanges) {
     __ ldr(R1, Address(SP, 0 * kWordSize));
     if (num_args == 2) {
       __ ldr(R3, Address(SP, 1 * kWordSize));
     }
@@ skipping 563 matching lines @@
   const Register right = R0;
   __ LoadFromOffset(left, SP, 1 * kWordSize, kNoPP);
   __ LoadFromOffset(right, SP, 0 * kWordSize, kNoPP);
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64