Improve code generation for bounds checks.

src/x64/lithium-x64.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 1771 matching lines @@
   LInstruction* result = new(zone()) LSeqStringSetChar(context, string,
                                                        index, value);
   if (FLAG_debug_code) {
     result = MarkAsCall(result, instr);
   }
   return result;
 }
 
 
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
-  LOperand* value = UseRegisterOrConstantAtStart(instr->index());
-  LOperand* length = Use(instr->length());
-  return AssignEnvironment(new(zone()) LBoundsCheck(value, length));
+  if (!FLAG_debug_code && instr->skip_check()) return NULL;
+  LOperand* index = UseRegisterOrConstantAtStart(instr->index());
+  LOperand* length = !index->IsConstantOperand()
+      ? UseOrConstantAtStart(instr->length())
+      : UseAtStart(instr->length());
+  LInstruction* result = new(zone()) LBoundsCheck(index, length);
+  if (!FLAG_debug_code || !instr->skip_check()) {
+    result = AssignEnvironment(result);
+  }
+  return result;
 }
 
 
 LInstruction* LChunkBuilder::DoBoundsCheckBaseIndexInformation(
     HBoundsCheckBaseIndexInformation* instr) {
   UNREACHABLE();
   return NULL;
 }
 
 
@@ skipping 795 matching lines @@
   LOperand* index = UseTempRegister(instr->index());
   LLoadFieldByIndex* load = new(zone()) LLoadFieldByIndex(object, index);
   LInstruction* result = DefineSameAsFirst(load);
   return AssignPointerMap(result);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64