With >= 64 non-string instance types, I removed an optimization

src/ia32/code-stubs-ia32.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 4094 matching lines @@
 }
 
 
 static void BranchIfNotInternalizedString(MacroAssembler* masm,
                                           Label* label,
                                           Register object,
                                           Register scratch) {
   __ JumpIfSmi(object, label);
   __ mov(scratch, FieldOperand(object, HeapObject::kMapOffset));
   __ movzx_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
-  __ and_(scratch, kIsInternalizedMask | kIsNotStringMask);
-  __ cmp(scratch, kInternalizedTag | kStringTag);
+  __ and_(scratch, kIsNotStringMask | kIsNotInternalizedMask);
+  __ cmp(scratch, kStringTag | kInternalizedTag);

[Yang, 2013/07/19 09:52:18]

change that to a test, saving one instruction.

[mvstanton, 2013/07/19 11:07:42]

Done. It's done on x64 as well (ARM is formulated differently).

   __ j(not_equal, label);
 }
 
 
 void ICCompareStub::GenerateGeneric(MacroAssembler* masm) {
   Label check_unequal_objects;
   Condition cc = GetCondition();
 
   Label miss;
   CheckInputType(masm, edx, left_, &miss);
@@ skipping 2475 matching lines @@
   __ mov(tmp1, left);
   STATIC_ASSERT(kSmiTag == 0);
   __ and_(tmp1, right);
   __ JumpIfSmi(tmp1, &miss, Label::kNear);
 
   // Check that both operands are internalized strings.
   __ mov(tmp1, FieldOperand(left, HeapObject::kMapOffset));
   __ mov(tmp2, FieldOperand(right, HeapObject::kMapOffset));
   __ movzx_b(tmp1, FieldOperand(tmp1, Map::kInstanceTypeOffset));
   __ movzx_b(tmp2, FieldOperand(tmp2, Map::kInstanceTypeOffset));
-  STATIC_ASSERT(kInternalizedTag != 0);
-  __ and_(tmp1, Immediate(kIsNotStringMask | kIsInternalizedMask));
-  __ cmpb(tmp1, kInternalizedTag | kStringTag);
-  __ j(not_equal, &miss, Label::kNear);
-
-  __ and_(tmp2, Immediate(kIsNotStringMask | kIsInternalizedMask));
-  __ cmpb(tmp2, kInternalizedTag | kStringTag);
-  __ j(not_equal, &miss, Label::kNear);
+  STATIC_ASSERT(kInternalizedTag == 0 && kStringTag == 0);
+  __ or_(tmp1, tmp2);
+  __ test(tmp1, Immediate(kIsNotStringMask | kIsNotInternalizedMask));
+  __ j(not_zero, &miss, Label::kNear);
 
   // Internalized strings are compared by identity.
   Label done;
   __ cmp(left, right);
   // Make sure eax is non-zero. At this point input operands are
   // guaranteed to be non-zero.
   ASSERT(right.is(eax));
   __ j(not_equal, &done, Label::kNear);
   STATIC_ASSERT(EQUAL == 0);
   STATIC_ASSERT(kSmiTag == 0);
@@ skipping 18 matching lines @@
 
   // Check that both operands are heap objects.
   Label miss;
   __ mov(tmp1, left);
   STATIC_ASSERT(kSmiTag == 0);
   __ and_(tmp1, right);
   __ JumpIfSmi(tmp1, &miss, Label::kNear);
 
   // Check that both operands are unique names. This leaves the instance
   // types loaded in tmp1 and tmp2.
-  STATIC_ASSERT(kInternalizedTag != 0);
   __ mov(tmp1, FieldOperand(left, HeapObject::kMapOffset));
   __ mov(tmp2, FieldOperand(right, HeapObject::kMapOffset));
   __ movzx_b(tmp1, FieldOperand(tmp1, Map::kInstanceTypeOffset));
   __ movzx_b(tmp2, FieldOperand(tmp2, Map::kInstanceTypeOffset));
 
   __ JumpIfNotUniqueName(tmp1, &miss, Label::kNear);
   __ JumpIfNotUniqueName(tmp2, &miss, Label::kNear);
 
   // Unique names are compared by identity.
   Label done;
@@ skipping 55 matching lines @@
 
   // Handle not identical strings.
   __ bind(&not_same);
 
   // Check that both strings are internalized. If they are, we're done
   // because we already know they are not identical.  But in the case of
   // non-equality compare, we still need to determine the order. We
   // also know they are both strings.
   if (equality) {
     Label do_compare;
-    STATIC_ASSERT(kInternalizedTag != 0);
-    __ and_(tmp1, tmp2);
-    __ test(tmp1, Immediate(kIsInternalizedMask));
-    __ j(zero, &do_compare, Label::kNear);
+    STATIC_ASSERT(kInternalizedTag == 0);
+    __ or_(tmp1, tmp2);
+    __ test(tmp1, Immediate(kIsNotInternalizedMask));
+    __ j(not_zero, &do_compare, Label::kNear);
     // Make sure eax is non-zero. At this point input operands are
     // guaranteed to be non-zero.
     ASSERT(right.is(eax));
     __ ret(0);
     __ bind(&do_compare);
   }
 
   // Check that both strings are sequential ASCII.
   Label runtime;
   __ JumpIfNotBothSequentialAsciiStrings(left, right, tmp1, tmp2, &runtime);
@@ skipping 1033 matching lines @@
   __ bind(&fast_elements_case);
   GenerateCase(masm, FAST_ELEMENTS);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32