MIPS: Fixing performance regression in issue 1787.

src/mips/code-stubs-mips.cc

 // Copyright 2011 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 7094 matching lines @@
 // |done| label if a property with the given name is found. Jump to
 // the |miss| label otherwise.
 // If lookup was successful |scratch2| will be equal to elements + 4 * index.
 void StringDictionaryLookupStub::GeneratePositiveLookup(MacroAssembler* masm,
                                                         Label* miss,
                                                         Label* done,
                                                         Register elements,
                                                         Register name,
                                                         Register scratch1,
                                                         Register scratch2) {
+  ASSERT(!elements.is(scratch1));
+  ASSERT(!elements.is(scratch2));
+  ASSERT(!name.is(scratch1));
+  ASSERT(!name.is(scratch2));
+
   // Assert that name contains a string.
   if (FLAG_debug_code) __ AbortIfNotString(name);
 
   // Compute the capacity mask.
   __ lw(scratch1, FieldMemOperand(elements, kCapacityOffset));
   __ sra(scratch1, scratch1, kSmiTagSize);  // convert smi to int
   __ Subu(scratch1, scratch1, Operand(1));
 
   // Generate an unrolled loop that performs a few probes before
   // giving up. Measurements done on Gmail indicate that 2 probes
@@ skipping 416 matching lines @@
 
   // Fall through when we need to inform the incremental marker.
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS