Optimize one byte string comparisons.

runtime/vm/intermediate_language_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"  // Needed here to get TARGET_ARCH_ARM.
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 727 matching lines @@
 void StringFromCharCodeInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register char_code = locs()->in(0).reg();
   Register result = locs()->out().reg();
   __ LoadImmediate(result,
                    reinterpret_cast<uword>(Symbols::PredefinedAddress()));
   __ AddImmediate(result, Symbols::kNullCharCodeSymbolOffset * kWordSize);
   __ ldr(result, Address(result, char_code, LSL, 1));  // Char code is a smi.
 }
 
 
+LocationSummary* StringToCharCodeInstr::MakeLocationSummary(bool opt) const {
+  const intptr_t kNumInputs = 1;
+  return LocationSummary::Make(kNumInputs,
+                               Location::RequiresRegister(),
+                               LocationSummary::kNoCall);
+}
+
+
+void StringToCharCodeInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  ASSERT(cid_ == kOneByteStringCid);
+  Register str = locs()->in(0).reg();
+  Register result = locs()->out().reg();
+  __ ldr(result, FieldAddress(str, String::length_offset()));
+  __ cmp(result, ShifterOperand(Smi::RawValue(1)));
+  __ LoadImmediate(result, Smi::RawValue(-1), NE);
+  __ ldrb(result, FieldAddress(str, OneByteString::data_offset()), EQ);
+  __ SmiTag(result);
+}
+
+
 LocationSummary* StringInterpolateInstr::MakeLocationSummary(bool opt) const {
   const intptr_t kNumInputs = 1;
   const intptr_t kNumTemps = 0;
   LocationSummary* summary =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kCall);
   summary->set_in(0, Location::RegisterLocation(R0));
   summary->set_out(Location::RegisterLocation(R0));
   return summary;
 }
 
@@ skipping 4068 matching lines @@
   compiler->GenerateCall(token_pos(),
                          &label,
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM