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 702 matching lines @@
   __ LoadImmediate(R5, entry);
   __ LoadImmediate(R1, NativeArguments::ComputeArgcTag(function()));
   compiler->GenerateCall(token_pos(),
                          stub_entry,
                          PcDescriptors::kOther,
                          locs());
   __ Pop(result);
 }
 
 
-LocationSummary* StringFromCharCodeInstr::MakeLocationSummary(bool opt) const {
+LocationSummary* StringCharCodeInstr::MakeLocationSummary(bool opt) const {
   const intptr_t kNumInputs = 1;
   // TODO(fschneider): Allow immediate operands for the char code.
   return LocationSummary::Make(kNumInputs,
                                Location::RequiresRegister(),
                                LocationSummary::kNoCall);
 }
 
 
-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.
+void StringCharCodeInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  if (kind() == StringCharCodeInstr::kFromCharCode) {
+    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.
+  } else {
+    ASSERT(kind() == StringCharCodeInstr::kToCharCode);
+    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));
@@ skipping 4071 matching lines @@
   compiler->GenerateCall(token_pos(),
                          &label,
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM