Improve smi code for truncating division(~/) by using two fewer temp registers.

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 1805 matching lines @@
   __ cmpl(ESP,
           Address::Absolute(Isolate::Current()->stack_limit_address()));
   __ j(BELOW_EQUAL, slow_path->entry_label());
   __ Bind(slow_path->exit_label());
 }
 
 
 LocationSummary* BinarySmiOpInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
   if (op_kind() == Token::kTRUNCDIV) {
-    const intptr_t kNumTemps = 3;
+    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::RegisterLocation(ECX));
+    summary->set_in(1, Location::WritableRegister());
     summary->set_out(Location::SameAsFirstInput());
-    summary->set_temp(0, Location::RegisterLocation(EBX));
-    // Will be used for for sign extension.
-    summary->set_temp(1, Location::RegisterLocation(EDX));
-    summary->set_temp(2, Location::RequiresRegister());
+    // 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 141 matching lines @@
       // No overflow check.
       __ orl(left, right);
       break;
     }
     case Token::kBIT_XOR: {
       // No overflow check.
       __ xorl(left, right);
       break;
     }
     case Token::kTRUNCDIV: {
-      Register temp = locs()->temp(0).reg();
       // Handle divide by zero in runtime.
-      // Deoptimization requires that temp and right are preserved.
       __ testl(right, right);
       __ j(ZERO, deopt);
       ASSERT(left == EAX);
       ASSERT((right != EDX) && (right != EAX));
-      ASSERT((temp != EDX) && (temp != EAX));
-      ASSERT(locs()->temp(1).reg() == EDX);
+      ASSERT(locs()->temp(0).reg() == EDX);
       ASSERT(result == EAX);
-      Register right_temp = locs()->temp(2).reg();
-      __ movl(right_temp, right);
       __ SmiUntag(left);
-      __ SmiUntag(right_temp);
+      __ SmiUntag(right);
       __ cdq();  // Sign extend EAX -> EDX:EAX.
-      __ idivl(right_temp);  //  EAX: quotient, EDX: remainder.
+      __ idivl(right);  //  EAX: quotient, EDX: remainder.
       // Check the corner case of dividing the 'MIN_SMI' with -1, in which
       // case we cannot tag the result.
       __ cmpl(result, Immediate(0x40000000));
       __ j(EQUAL, deopt);
       __ SmiTag(result);
       break;
     }
     case Token::kSHR: {
       if (CanDeoptimize()) {
         __ cmpl(right, Immediate(0));
@@ skipping 1192 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_IA32