Optimize one byte string comparisons.

runtime/vm/intermediate_language_x64.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_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 634 matching lines @@
   const Object& constant = index->definition()->AsConstant()->value();
   if (!constant.IsSmi()) return false;
   const Smi& smi_const = Smi::Cast(constant);
   const intptr_t scale = FlowGraphCompiler::ElementSizeFor(cid);
   const intptr_t data_offset = FlowGraphCompiler::DataOffsetFor(cid);
   const int64_t disp = smi_const.AsInt64Value() * scale + data_offset;
   return Utils::IsInt(32, disp);
 }
 
 
-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,
-          Immediate(reinterpret_cast<uword>(Symbols::PredefinedAddress())), PP);
-  __ movq(result, Address(result,
-                          char_code,
-                          TIMES_HALF_WORD_SIZE,  // Char code is a smi.
-                          Symbols::kNullCharCodeSymbolOffset * kWordSize));
+void StringCharCodeInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  if (kind() == StringCharCodeInstr::kFromCharCode) {
+    ASSERT(kind() == StringCharCodeInstr::kFromCharCode);
+    Register char_code = locs()->in(0).reg();
+    Register result = locs()->out().reg();
+    __ LoadImmediate(result,
+        Immediate(reinterpret_cast<uword>(Symbols::PredefinedAddress())), PP);
+    __ movq(result, Address(result,
+                            char_code,
+                            TIMES_HALF_WORD_SIZE,  // Char code is a smi.
+                            Symbols::kNullCharCodeSymbolOffset * kWordSize));
+  } else {
+    ASSERT(kind() == StringCharCodeInstr::kToCharCode);
+    ASSERT(cid_ == kOneByteStringCid);
+    Register str = locs()->in(0).reg();
+    Register result = locs()->out().reg();
+    Label is_one, done;
+    __ movq(result, FieldAddress(str, String::length_offset()));
+    __ cmpq(result, Immediate(Smi::RawValue(1)));
+    __ j(EQUAL, &is_one, Assembler::kNearJump);
+    __ movq(result, Immediate(Smi::RawValue(-1)));
+    __ jmp(&done);
+    __ Bind(&is_one);
+    __ movzxb(result, FieldAddress(str, OneByteString::data_offset()));
+    __ SmiTag(result);
+    __ Bind(&done);
+  }
 }
 
 
 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(RAX));
   summary->set_out(Location::RegisterLocation(RAX));
@@ skipping 4256 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64