Optimize smi multiply by 2 using shl by 1.

runtime/vm/intermediate_language_x64.cc

 // Copyright (c) 2013, 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_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 1816 matching lines @@
   const bool is_truncating = shift_left->is_truncating();
   const LocationSummary& locs = *shift_left->locs();
   Register left = locs.in(0).reg();
   Register result = locs.out().reg();
   ASSERT(left == result);
   Label* deopt = shift_left->CanDeoptimize() ?
       compiler->AddDeoptStub(shift_left->deopt_id(), kDeoptBinarySmiOp) : NULL;
   if (locs.in(1).IsConstant()) {
     const Object& constant = locs.in(1).constant();
     ASSERT(constant.IsSmi());
-    // shll operation masks the count to 6 bits.
+    // shlq operation masks the count to 6 bits.
     const intptr_t kCountLimit = 0x3F;
     const intptr_t value = Smi::Cast(constant).Value();
     if (value == 0) {
       // No code needed.
     } else if ((value < 0) || (value >= kCountLimit)) {
       // This condition may not be known earlier in some cases because
       // of constant propagation, inlining, etc.
       if ((value >=kCountLimit) && is_truncating) {
         __ xorq(result, result);
       } else {
@@ skipping 200 matching lines @@
         break;
       }
       case Token::kSUB: {
         __ subq(left, Immediate(imm));
         if (deopt != NULL) __ j(OVERFLOW, deopt);
         break;
       }
       case Token::kMUL: {
         // Keep left value tagged and untag right value.
         const intptr_t value = Smi::Cast(constant).Value();
-        __ imulq(left, Immediate(value));
+        if (value == 2) {
+          __ shlq(left, Immediate(1));
+        } else {
+          __ imulq(left, Immediate(value));
+        }
         if (deopt != NULL) __ j(OVERFLOW, deopt);
         break;
       }
       case Token::kTRUNCDIV: {
         const intptr_t value = Smi::Cast(constant).Value();
         if (value == 1) {
           // Do nothing.
           break;
         } else if (value == -1) {
           // Check the corner case of dividing the 'MIN_SMI' with -1, in which
@@ skipping 1099 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64