MIPS: Improve array to string conversion.

src/mips/codegen-mips.cc

Index: src/mips/codegen-mips.cc
diff --git a/src/mips/codegen-mips.cc b/src/mips/codegen-mips.cc
index 0119c11f53b27102b3dda4aa5b18e8eb259b6054..ded0821a8439a89d0b5501d9d5b9e323939f3e60 100644
--- a/src/mips/codegen-mips.cc
+++ b/src/mips/codegen-mips.cc
@@ -517,6 +517,50 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
 }
 
 
+void SeqStringSetCharGenerator::Generate(MacroAssembler* masm,
+                                         String::Encoding encoding,
+                                         Register string,
+                                         Register index,
+                                         Register value) {
+  if (FLAG_debug_code) {
+    __ And(at, index, Operand(kSmiTagMask));
+    __ Check(eq, "Non-smi index", at, Operand(zero_reg));
+    __ And(at, value, Operand(kSmiTagMask));
+    __ Check(eq, "Non-smi value", at, Operand(zero_reg));
+
+    __ lw(at, FieldMemOperand(string, String::kLengthOffset));
+    __ Check(lt, "Index is too large", at, Operand(index));
+
+    __ Check(ge, "Index is negative", index, Operand(Smi::FromInt(0)));
+
+    __ lw(at, FieldMemOperand(string, HeapObject::kMapOffset));
+    __ lbu(at, FieldMemOperand(at, Map::kInstanceTypeOffset));
+
+    __ And(at, at, Operand(kStringRepresentationMask | kStringEncodingMask));
+    static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
+    static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
+    __ Check(eq, "Unexpected string type", at,
+        Operand(encoding == String::ONE_BYTE_ENCODING
+                    ? one_byte_seq_type : two_byte_seq_type));
+  }
+
+  __ Addu(at,
+          string,
+          Operand(SeqString::kHeaderSize - kHeapObjectTag));
+  __ SmiUntag(value);
+  STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
+  if (encoding == String::ONE_BYTE_ENCODING) {
+    __ SmiUntag(index);
+    __ Addu(at, at, index);
+    __ sb(value, MemOperand(at));
+  } else {
+    // No need to untag a smi for two-byte addressing.
+    __ Addu(at, at, index);
+    __ sh(value, MemOperand(at));
+  }
+}
+
+
 static MemOperand ExpConstant(int index, Register base) {
   return MemOperand(base, index * kDoubleSize);
 }