Simplify StringCharCodeAt in non-crankshaft codegen.

src/ia32/code-stubs-ia32.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5089 matching lines @@
   __ mov(result_, FieldOperand(object_, HeapObject::kMapOffset));
   __ movzx_b(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   // If the receiver is not a string trigger the non-string case.
   __ test(result_, Immediate(kIsNotStringMask));
   __ j(not_zero, receiver_not_string_);
 
   // If the index is non-smi trigger the non-smi case.
   STATIC_ASSERT(kSmiTag == 0);
   __ JumpIfNotSmi(index_, &index_not_smi_);
 
   // Put smi-tagged index into scratch register.

[Lasse Reichstein, 2011/11/09 12:48:11]

Remove the comment too.

-  __ mov(scratch_, index_);
   __ bind(&got_smi_index_);
 
   // Check for index out of range.
-  __ cmp(scratch_, FieldOperand(object_, String::kLengthOffset));
+  __ cmp(index_, FieldOperand(object_, String::kLengthOffset));
   __ j(above_equal, index_out_of_range_);
 
   // We need special handling for non-flat strings.
   STATIC_ASSERT(kSeqStringTag == 0);
   __ test(result_, Immediate(kStringRepresentationMask));
   __ j(zero, &flat_string);
 
   // Handle non-flat strings.
   __ and_(result_, kStringRepresentationMask);
   STATIC_ASSERT(kConsStringTag < kExternalStringTag);
   STATIC_ASSERT(kSlicedStringTag > kExternalStringTag);
   __ cmp(result_, kExternalStringTag);
   __ j(greater, &sliced_string, Label::kNear);
   __ j(equal, &call_runtime_);
 
   // ConsString.
   // Check whether the right hand side is the empty string (i.e. if
   // this is really a flat string in a cons string). If that is not
   // the case we would rather go to the runtime system now to flatten
   // the string.
   Label assure_seq_string;
   __ cmp(FieldOperand(object_, ConsString::kSecondOffset),
          Immediate(masm->isolate()->factory()->empty_string()));
   __ j(not_equal, &call_runtime_);
-  // Get the first of the two strings and load its instance type.
-  __ mov(result_, FieldOperand(object_, ConsString::kFirstOffset));
+  // Get the first of the two parts.
+  __ mov(object_, FieldOperand(object_, ConsString::kFirstOffset));
   __ jmp(&assure_seq_string, Label::kNear);
 
   // SlicedString, unpack and add offset.
   __ bind(&sliced_string);
-  __ add(scratch_, FieldOperand(object_, SlicedString::kOffsetOffset));
-  __ mov(result_, FieldOperand(object_, SlicedString::kParentOffset));
+  __ add(index_, FieldOperand(object_, SlicedString::kOffsetOffset));
+  __ mov(object_, FieldOperand(object_, SlicedString::kParentOffset));
 
   // Assure that we are dealing with a sequential string. Go to runtime if not.
+  // Note that if the original string is a cons or slice with an external
+  // string as underlying string, we pass that unpacked underlying string with
+  // the updated index to the runtime function.
   __ bind(&assure_seq_string);
-  __ mov(result_, FieldOperand(result_, HeapObject::kMapOffset));
+  __ mov(result_, FieldOperand(object_, HeapObject::kMapOffset));
   __ movzx_b(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   STATIC_ASSERT(kSeqStringTag == 0);
   __ test(result_, Immediate(kStringRepresentationMask));
   __ j(not_zero, &call_runtime_);
-  // Actually fetch the parent string if it is confirmed to be sequential.
-  STATIC_ASSERT(SlicedString::kParentOffset == ConsString::kFirstOffset);
-  __ mov(object_, FieldOperand(object_, SlicedString::kParentOffset));
 
   // Check for 1-byte or 2-byte string.
   __ bind(&flat_string);
   STATIC_ASSERT((kStringEncodingMask & kAsciiStringTag) != 0);
   STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
   __ test(result_, Immediate(kStringEncodingMask));
   __ j(not_zero, &ascii_string, Label::kNear);
 
   // 2-byte string.
   // Load the 2-byte character code into the result register.
   STATIC_ASSERT(kSmiTag == 0 && kSmiTagSize == 1);
   __ movzx_w(result_, FieldOperand(object_,
-                                   scratch_, times_1,  // Scratch is smi-tagged.
+                                   index_, times_1,  // Scratch is smi-tagged.
                                    SeqTwoByteString::kHeaderSize));
   __ jmp(&got_char_code, Label::kNear);
 
   // ASCII string.
   // Load the byte into the result register.
   __ bind(&ascii_string);
-  __ SmiUntag(scratch_);
+  __ SmiUntag(index_);
   __ movzx_b(result_, FieldOperand(object_,
-                                   scratch_, times_1,
+                                   index_, times_1,
                                    SeqAsciiString::kHeaderSize));
   __ bind(&got_char_code);
   __ SmiTag(result_);
   __ bind(&exit_);
 }
 
 
 void StringCharCodeAtGenerator::GenerateSlow(
     MacroAssembler* masm,
     const RuntimeCallHelper& call_helper) {
   __ Abort("Unexpected fallthrough to CharCodeAt slow case");
 
   // Index is not a smi.
   __ bind(&index_not_smi_);
   // If index is a heap number, try converting it to an integer.
   __ CheckMap(index_,
               masm->isolate()->factory()->heap_number_map(),
               index_not_number_,
               DONT_DO_SMI_CHECK);
   call_helper.BeforeCall(masm);
   __ push(object_);
-  __ push(index_);
   __ push(index_);  // Consumed by runtime conversion function.
   if (index_flags_ == STRING_INDEX_IS_NUMBER) {
     __ CallRuntime(Runtime::kNumberToIntegerMapMinusZero, 1);
   } else {
     ASSERT(index_flags_ == STRING_INDEX_IS_ARRAY_INDEX);
     // NumberToSmi discards numbers that are not exact integers.
     __ CallRuntime(Runtime::kNumberToSmi, 1);
   }
-  if (!scratch_.is(eax)) {
+  if (!index_.is(eax)) {
     // Save the conversion result before the pop instructions below
     // have a chance to overwrite it.
-    __ mov(scratch_, eax);
+    __ mov(index_, eax);
   }
-  __ pop(index_);
   __ pop(object_);
   // Reload the instance type.
   __ mov(result_, FieldOperand(object_, HeapObject::kMapOffset));
   __ movzx_b(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   call_helper.AfterCall(masm);
   // If index is still not a smi, it must be out of range.
   STATIC_ASSERT(kSmiTag == 0);
-  __ JumpIfNotSmi(scratch_, index_out_of_range_);
+  __ JumpIfNotSmi(index_, index_out_of_range_);
   // Otherwise, return to the fast path.
   __ jmp(&got_smi_index_);
 
   // Call runtime. We get here when the receiver is a string and the
   // index is a number, but the code of getting the actual character
   // is too complex (e.g., when the string needs to be flattened).
   __ bind(&call_runtime_);
   call_helper.BeforeCall(masm);
   __ push(object_);
   __ push(index_);
@@ skipping 1878 matching lines @@
     __ bind(&element_done);
     __ ret(0);
   }
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32