Separate the array/string .length load from the bounds check.

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 "lib/error.h"
@@ skipping 2564 matching lines @@
   __ testq(value, Immediate(kSmiTagMask));
   __ j(NOT_ZERO, deopt);
 }
 
 
 LocationSummary* CheckArrayBoundInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
   const intptr_t kNumTemps = 0;
   LocationSummary* locs =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
-  locs->set_in(0, Location::RegisterOrSmiConstant(array()));
+  locs->set_in(0, Location::RegisterOrSmiConstant(length()));
   locs->set_in(1, Location::RegisterOrSmiConstant(index()));
   return locs;
 }
 
 
 void CheckArrayBoundInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Label* deopt = compiler->AddDeoptStub(deopt_id(),
                                         kDeoptCheckArrayBound);
   if (locs()->in(0).IsConstant() && locs()->in(1).IsConstant()) {
     // Unconditionally deoptimize for constant bounds checks because they
     // only occur only when index is out-of-bounds.
     __ jmp(deopt);
     return;
   }
 
-
-  intptr_t length_offset = LengthOffsetFor(array_type());
   if (locs()->in(1).IsConstant()) {
-    Register receiver = locs()->in(0).reg();
+    Register length = locs()->in(0).reg();
     const Object& constant = locs()->in(1).constant();
     ASSERT(constant.IsSmi());
     const int64_t imm =
         reinterpret_cast<int64_t>(constant.raw());
-    __ cmpq(FieldAddress(receiver, length_offset), Immediate(imm));
+    __ cmpq(length, Immediate(imm));
     __ j(BELOW_EQUAL, deopt);
   } else if (locs()->in(0).IsConstant()) {
-    ASSERT(locs()->in(0).constant().IsArray() ||
-           locs()->in(0).constant().IsString());
-    intptr_t length = locs()->in(0).constant().IsArray()
-        ? Array::Cast(locs()->in(0).constant()).Length()
-        : String::Cast(locs()->in(0).constant()).Length();
+    ASSERT(locs()->in(0).constant().IsSmi());
+    const Smi& smi_const = Smi::Cast(locs()->in(0).constant());
     Register index = locs()->in(1).reg();
-    __ cmpq(index,
-        Immediate(reinterpret_cast<int64_t>(Smi::New(length))));
+    __ cmpq(index, Immediate(reinterpret_cast<int64_t>(smi_const.raw())));
     __ j(ABOVE_EQUAL, deopt);
   } else {
-    Register receiver = locs()->in(0).reg();
+    Register length = locs()->in(0).reg();
     Register index = locs()->in(1).reg();
-    __ cmpq(index, FieldAddress(receiver, length_offset));
+    __ cmpq(index, length);
     __ j(ABOVE_EQUAL, deopt);
   }
 }
 
 
 LocationSummary* UnboxIntegerInstr::MakeLocationSummary() const {
   UNIMPLEMENTED();
   return NULL;
 }
 
@@ skipping 357 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64