Fixing performance regression in issue 1787.

src/arm/code-stubs-arm.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 6821 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.
   __ ldr(scratch1, FieldMemOperand(elements, kCapacityOffset));
   __ mov(scratch1, Operand(scratch1, ASR, kSmiTagSize));  // convert smi to int
   __ sub(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 23 matching lines @@
     __ cmp(name, Operand(ip));
     __ b(eq, done);
   }
 
   const int spill_mask =
       (lr.bit() | r6.bit() | r5.bit() | r4.bit() |
        r3.bit() | r2.bit() | r1.bit() | r0.bit()) &
       ~(scratch1.bit() | scratch2.bit());
 
   __ stm(db_w, sp, spill_mask);
-  __ Move(r0, elements);
-  __ Move(r1, name);
+  if (name.is(r0)) {
+    ASSERT(!elements.is(r1));
+    __ Move(r1, name);
+    __ Move(r0, elements);
+  } else {
+    __ Move(r0, elements);
+    __ Move(r1, name);
+  }
   StringDictionaryLookupStub stub(POSITIVE_LOOKUP);
   __ CallStub(&stub);
   __ tst(r0, Operand(r0));
   __ mov(scratch2, Operand(r2));
   __ ldm(ia_w, sp, spill_mask);
 
   __ b(ne, done);
   __ b(eq, miss);
 }
 
@@ skipping 355 matching lines @@
   __ bind(&need_incremental);
 
   // Fall through when we need to inform the incremental marker.
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM