Improve implementation of HSeqStringSetChar.

src/arm/lithium-codegen-arm.cc

 // Copyright 2012 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 1906 matching lines @@
     }
     __ bind(&runtime);
     __ PrepareCallCFunction(2, scratch);
     __ mov(r1, Operand(index));
     __ CallCFunction(ExternalReference::get_date_field_function(isolate()), 2);
     __ bind(&done);
   }
 }
 
 
+MemOperand LCodeGen::BuildSeqStringOperand(Register string,
+                                           LOperand* index,
+                                           String::Encoding encoding) {
+  if (index->IsConstantOperand()) {
+    int offset = ToInteger32(LConstantOperand::cast(index));
+    if (encoding == String::TWO_BYTE_ENCODING) {
+      offset *= kUC16Size;
+    }
+    STATIC_ASSERT(kCharSize == 1);
+    return FieldMemOperand(string, SeqString::kHeaderSize + offset);
+  }
+  Register scratch = scratch0();
+  ASSERT(!scratch.is(string));
+  ASSERT(!scratch.is(ToRegister(index)));
+  if (encoding == String::ONE_BYTE_ENCODING) {
+    __ add(scratch, string, Operand(ToRegister(index)));
+  } else {
+    STATIC_ASSERT(kUC16Size == 2);
+    __ add(scratch, string, Operand(ToRegister(index), LSL, 1));
+  }
+  return FieldMemOperand(scratch, SeqString::kHeaderSize);
+}
+
+
 void LCodeGen::DoSeqStringSetChar(LSeqStringSetChar* instr) {
+  String::Encoding encoding = instr->hydrogen()->encoding();
   Register string = ToRegister(instr->string());
-  LOperand* index_op = instr->index();
   Register value = ToRegister(instr->value());
-  Register scratch = scratch0();
-  String::Encoding encoding = instr->encoding();
 
   if (FLAG_debug_code) {
+    Register scratch = scratch0();
     __ ldr(scratch, FieldMemOperand(string, HeapObject::kMapOffset));
     __ ldrb(scratch, FieldMemOperand(scratch, Map::kInstanceTypeOffset));
 
     __ and_(scratch, scratch,
             Operand(kStringRepresentationMask | kStringEncodingMask));
     static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
     static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
     __ cmp(scratch, Operand(encoding == String::ONE_BYTE_ENCODING
                             ? one_byte_seq_type : two_byte_seq_type));
     __ Check(eq, kUnexpectedStringType);
   }
 
-  if (index_op->IsConstantOperand()) {
-    int constant_index = ToInteger32(LConstantOperand::cast(index_op));
-    if (encoding == String::ONE_BYTE_ENCODING) {
-      __ strb(value,
-              FieldMemOperand(string, SeqString::kHeaderSize + constant_index));
-    } else {
-      __ strh(value,
-          FieldMemOperand(string, SeqString::kHeaderSize + constant_index * 2));
-    }
+  MemOperand operand = BuildSeqStringOperand(string, instr->index(), encoding);
+  if (encoding == String::ONE_BYTE_ENCODING) {
+    __ strb(value, operand);
   } else {
-    Register index = ToRegister(index_op);
-    if (encoding == String::ONE_BYTE_ENCODING) {
-      __ add(scratch, string, Operand(index));
-      __ strb(value, FieldMemOperand(scratch, SeqString::kHeaderSize));
-    } else {
-      __ add(scratch, string, Operand(index, LSL, 1));
-      __ strh(value, FieldMemOperand(scratch, SeqString::kHeaderSize));
-    }
+    __ strh(value, operand);
   }
 }
 
 
 void LCodeGen::DoThrow(LThrow* instr) {
   Register input_reg = EmitLoadRegister(instr->value(), ip);
   __ push(input_reg);
   ASSERT(ToRegister(instr->context()).is(cp));
   CallRuntime(Runtime::kThrow, 1, instr);
 
@@ skipping 3851 matching lines @@
   __ sub(scratch, result, Operand::PointerOffsetFromSmiKey(index));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal