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

runtime/vm/intermediate_language_ia32.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_IA32.
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 1936 matching lines @@
   __ Bind(slow_path->exit_label());
 }
 
 
 LocationSummary* BinarySmiOpInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
   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(EAX));
-    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(EDX));
+    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(EAX));
+      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(EDX));
+    }
     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(), ECX));
     summary->set_out(Location::SameAsFirstInput());
     return summary;
   } else if (op_kind() == Token::kSHL) {
@@ skipping 16 matching lines @@
   }
 }
 
 
 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);
+    deopt  = compiler->AddDeoptStub(deopt_id(), kDeoptBinarySmiOp);
   }
 
   if (locs()->in(1).IsConstant()) {
     const Object& constant = locs()->in(1).constant();
     ASSERT(constant.IsSmi());
     const int32_t imm =
         reinterpret_cast<int32_t>(constant.raw());
     switch (op_kind()) {
       case Token::kADD:
         __ addl(left, Immediate(imm));
         if (deopt != NULL) __ j(OVERFLOW, deopt);
         break;
       case Token::kSUB: {
         __ subl(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();
         __ imull(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.
+          __ cmpl(left, Immediate(0x80000000));
+          __ j(EQUAL, deopt);
+          __ negl(left);
+          break;
+        }
+        ASSERT((value != 0) && Utils::IsPowerOfTwo(Utils::Abs(value)));
+        const intptr_t shift_count =
+            Utils::ShiftForPowerOfTwo(Utils::Abs(value)) + kSmiTagSize;
+        Register temp = locs()->temp(0).reg();
+        __ movl(temp, left);
+        __ sarl(temp, Immediate(31));
+        if (shift_count > 1) {

[Florian Schneider, 2013/02/04 13:04:03]

Redundant if-statment? shift_count will only be 1 if the rhs value is 1 or -1
here. Those cases are already handled above.

[srdjan, 2013/02/04 19:02:33]

Removed

+          __ shrl(temp, Immediate(32 - shift_count));
+        }
+        __ addl(left, temp);
+        if (shift_count > 0) {

[Florian Schneider, 2013/02/04 13:04:03]

shift_count will always be > 0 here because kSmiTagSize == 1.

Maybe remove this if-statement and just ASSERT(kSmiTagSize >= 1).

[srdjan, 2013/02/04 19:02:33]

Done.

+          __ sarl(left, Immediate(shift_count));
+        }
+        if (value < 0) {
+          __ negl(left);
+        }
+        __ SmiTag(left);
+        break;
+      }
       case Token::kBIT_AND: {
         // No overflow check.
         __ andl(left, Immediate(imm));
         break;
       }
       case Token::kBIT_OR: {
         // No overflow check.
         __ orl(left, Immediate(imm));
         break;
       }
@@ skipping 1326 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_IA32