Implement Smi_bitLength intrinsic on mips, arm, and arm64.

runtime/vm/intrinsifier_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM64.
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/intrinsifier.h"
 
 #include "vm/assembler.h"
@@ skipping 674 matching lines @@
 
 void Intrinsifier::Smi_bitNegate(Assembler* assembler) {
   __ ldr(R0, Address(SP, 0 * kWordSize));
   __ mvn(R0, R0);
   __ andi(R0, R0, Immediate(~kSmiTagMask));  // Remove inverted smi-tag.
   __ ret();
 }
 
 
 void Intrinsifier::Smi_bitLength(Assembler* assembler) {
-  // TODO(sra): Implement as word-length - CLZ.
+  __ ldr(R0, Address(SP, 0 * kWordSize));
+  __ SmiUntag(R0);
+  // XOR with sign bit to complement bits if value is negative.
+  __ eor(R0, R0, Operand(R0, ASR, 63));
+  __ clz(R0, R0);
+  __ LoadImmediate(R1, 64, kNoPP);
+  __ sub(R0, R1, Operand(R0));
+  __ SmiTag(R0);
+  __ ret();
 }
 
 
 void Intrinsifier::Bigint_lsh(Assembler* assembler) {
   // static void _lsh(Uint32List x_digits, int x_used, int n,
   //                  Uint32List r_digits)
 
   // R2 = x_used, R3 = x_digits, x_used > 0, x_used is Smi.
   __ ldp(R2, R3, Address(SP, 2 * kWordSize, Address::PairOffset));
   __ add(R2, R2, Operand(2));  // x_used > 0, Smi. R2 = x_used + 1, round up.
@@ skipping 1397 matching lines @@
   Isolate* isolate = Isolate::Current();
   __ LoadImmediate(R1, reinterpret_cast<uword>(isolate), kNoPP);
   // Set return value to Isolate::current_tag_.
   __ ldr(R0, Address(R1, Isolate::current_tag_offset()));
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64