A64: Port LSeqStringSetChar optimizations from r16707 and r17521.

src/a64/macro-assembler-a64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
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 //
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@@ skipping 3603 matching lines @@
   // We want the smi-tagged index in key.  kArrayIndexValueMask has zeros in
   // the low kHashShift bits.
   STATIC_ASSERT(kSmiTag == 0);
   Ubfx(hash, hash, String::kHashShift, String::kArrayIndexValueBits);
   SmiTag(index, hash);
 }
 
 
 void MacroAssembler::EmitSeqStringSetCharCheck(Register string,
                                                Register index,
+                                               bool index_is_smi,
+                                               Register scratch,
                                                uint32_t encoding_mask) {
-  Register scratch = __ Tmp1();
   ASSERT(!AreAliased(string, index, scratch));
 
-  AssertSmi(index);
+  if (index_is_smi) {
+    AssertSmi(index);
+  }
 
   // Check that string is an object.
   ThrowIfSmi(string, kNonObject);
 
   // Check that string has an appropriate map.
   Ldr(scratch, FieldMemOperand(string, HeapObject::kMapOffset));
   Ldrb(scratch, FieldMemOperand(scratch, Map::kInstanceTypeOffset));
+
   And(scratch, scratch, kStringRepresentationMask | kStringEncodingMask);
   Cmp(scratch, encoding_mask);
   ThrowIf(ne, kUnexpectedStringType);
 
-  // Check that the index points inside the string.
   Ldr(scratch, FieldMemOperand(string, String::kLengthOffset));
-  Cmp(index, scratch);
+  Cmp(index, index_is_smi ? scratch : Operand::UntagSmi(scratch));
   ThrowIf(ge, kIndexIsTooLarge);
 
   Cmp(index, Operand(Smi::FromInt(0)));

[baptiste.afsa1, 2014/02/06 15:48:13]

Although it will work, it doesn't really make sense to compare with
Smi::FromInt(0) when the index is not a SMI.

Maybe you should compare with 0 and assert that Smi::FromInt(0) == 0 with a
comment explaining what's going on here.

[ulan, 2014/02/06 16:06:14]

I added assert, but didn't add comment since the assert and the code above makes
it clear.

   ThrowIf(lt, kIndexIsNegative);
 }
 
 
 void MacroAssembler::CheckAccessGlobalProxy(Register holder_reg,
                                             Register scratch,
                                             Label* miss) {
   // TODO(jbramley): Sort out the uses of Tmp0() and Tmp1() in this function.
   // The ARM version takes two scratch registers, and that should be enough for
   // all of the checks.
@@ skipping 1180 matching lines @@
   }
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_A64