MIPS: Convert String array index/length hash to BitField.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index d2fa8dec69e93c01d54e1308e4baa1b1e0740ee7..d2b1462f108675b128c04c4539075bc9ec7a260b 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -3999,19 +3999,14 @@ bool MacroAssembler::AllowThisStubCall(CodeStub* stub) {
 }
 
 
-void MacroAssembler::IndexFromHash(Register hash,
-                                   Register index) {
+void MacroAssembler::IndexFromHash(Register hash, Register index) {
   // If the hash field contains an array index pick it out. The assert checks
   // that the constants for the maximum number of digits for an array index
   // cached in the hash field and the number of bits reserved for it does not
   // conflict.
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
-  // We want the smi-tagged index in key.  kArrayIndexValueMask has zeros in
-  // the low kHashShift bits.
-  STATIC_ASSERT(kSmiTag == 0);
-  Ext(hash, hash, String::kHashShift, String::kArrayIndexValueBits);
-  sll(index, hash, kSmiTagSize);
+  DecodeFieldToSmi<String::ArrayIndexValueBits>(index, hash);
 }