Use SAR for positive divident by a power-of two constant divisor.

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 1768 matching lines @@
   __ j(BELOW_EQUAL, slow_path->entry_label());
   __ Bind(slow_path->exit_label());
 }
 
 
 static bool CanBeImmediate(const Object& constant) {
   return constant.IsSmi() &&
     Immediate(reinterpret_cast<int64_t>(constant.raw())).is_int32();
 }
 
+
 LocationSummary* BinarySmiOpInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
 
   ConstantInstr* right_constant = right()->definition()->AsConstant();
   if ((right_constant != NULL) &&
       (op_kind() != Token::kTRUNCDIV) &&
       (op_kind() != Token::kSHL) &&
       (op_kind() != Token::kMUL) &&
       CanBeImmediate(right_constant->value())) {
     const intptr_t kNumTemps = 0;
     LocationSummary* summary =
         new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
     summary->set_in(0, Location::RequiresRegister());
     summary->set_in(1, Location::Constant(right_constant->value()));
     summary->set_out(Location::SameAsFirstInput());
     return summary;
   }
 
   if (op_kind() == Token::kTRUNCDIV) {
     const intptr_t kNumTemps = 1;
     LocationSummary* summary =
         new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
-    // Both inputs must be writable because they will be untagged.
-    summary->set_in(0, Location::RegisterLocation(RAX));
-    summary->set_in(1, Location::WritableRegister());
-    summary->set_out(Location::SameAsFirstInput());
-    // Will be used for sign extension and division.
-    summary->set_temp(0, Location::RegisterLocation(RDX));
+    if (RightIsPowerOfTwoConstant()) {
+      summary->set_in(0, Location::RequiresRegister());
+      ConstantInstr* right_constant = right()->definition()->AsConstant();
+      summary->set_in(1, Location::Constant(right_constant->value()));
+      summary->set_temp(0, Location::RequiresRegister());
+      summary->set_out(Location::SameAsFirstInput());
+    } else {
+      // Both inputs must be writable because they will be untagged.
+      summary->set_in(0, Location::RegisterLocation(RAX));
+      summary->set_in(1, Location::WritableRegister());
+      summary->set_out(Location::SameAsFirstInput());
+      // Will be used for sign extension and division.
+      summary->set_temp(0, Location::RegisterLocation(RDX));
+    }
     return summary;
   } else if (op_kind() == Token::kSHR) {
     const intptr_t kNumTemps = 0;
     LocationSummary* summary =
         new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
     summary->set_in(0, Location::RequiresRegister());
     summary->set_in(1, Location::FixedRegisterOrSmiConstant(right(), RCX));
     summary->set_out(Location::SameAsFirstInput());
     return summary;
   } else if (op_kind() == Token::kSHL) {
     const intptr_t kNumTemps = 1;
     LocationSummary* summary =
         new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
     summary->set_in(0, Location::RequiresRegister());
     summary->set_in(1, Location::FixedRegisterOrSmiConstant(right(), RCX));
     summary->set_temp(0, Location::RequiresRegister());
     summary->set_out(Location::SameAsFirstInput());
     return summary;
   } else {
     const intptr_t kNumTemps = 0;
     LocationSummary* summary =
         new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
     summary->set_in(0, Location::RequiresRegister());
     summary->set_in(1, Location::RegisterOrSmiConstant(right()));
     summary->set_out(Location::SameAsFirstInput());
     return summary;
   }
 }
 
-
 void BinarySmiOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register left = locs()->in(0).reg();
   Register result = locs()->out().reg();
   ASSERT(left == result);
   Label* deopt = NULL;
   if (CanDeoptimize()) {
     deopt = compiler->AddDeoptStub(deopt_id(),
                                    kDeoptBinarySmiOp);
   }
 
@@ skipping 13 matching lines @@
         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 (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
+          // case we cannot negate the result.
+          __ cmpq(left, Immediate(0x8000000000000000));
+          __ j(EQUAL, deopt);
+          __ negq(left);
+          break;
+        }
+
+        ASSERT((value != 0) && Utils::IsPowerOfTwo(Utils::Abs(value)));
+        const intptr_t shift_count =
+            Utils::ShiftForPowerOfTwo(Utils::Abs(value)) + kSmiTagSize;
+        ASSERT(kSmiTagSize == 1);
+        Register temp = locs()->temp(0).reg();
+        __ movq(temp, left);
+        __ sarq(temp, Immediate(63));
+        ASSERT(shift_count > 1);  // 1, -1 case handled above.
+        __ shrq(temp, Immediate(64 - shift_count));
+        __ addq(left, temp);
+        ASSERT(shift_count > 0);
+        __ sarq(left, Immediate(shift_count));
+        if (value < 0) {
+          __ negq(left);
+        }
+        __ SmiTag(left);
+        break;
+      }
       case Token::kBIT_AND: {
         // No overflow check.
         __ andq(left, Immediate(imm));
         break;
       }
       case Token::kBIT_OR: {
         // No overflow check.
         __ orq(left, Immediate(imm));
         break;
       }
@@ skipping 1096 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64