A64: Port LSeqStringSetChar optimizations from r16707 and r17521.

src/a64/macro-assembler-a64.cc

Index: src/a64/macro-assembler-a64.cc
diff --git a/src/a64/macro-assembler-a64.cc b/src/a64/macro-assembler-a64.cc
index 685500306046946534f9938f066479752e7c99fe..f13ae64f847e6fcd84e65ea416c2f7edca98d8c8 100644
--- a/src/a64/macro-assembler-a64.cc
+++ b/src/a64/macro-assembler-a64.cc
@@ -3621,11 +3621,14 @@ void MacroAssembler::IndexFromHash(Register hash, Register index) {
 
 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);
@@ -3633,13 +3636,13 @@ void MacroAssembler::EmitSeqStringSetCharCheck(Register string,
   // 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.