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

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 1684 matching lines @@
     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 = 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(RAX));
-    summary->set_in(1, Location::RegisterLocation(RCX));
+    summary->set_in(1, Location::WritableRegister());
     summary->set_out(Location::SameAsFirstInput());
-    summary->set_temp(0, Location::RegisterLocation(RBX));
-    // Will be used for for sign extension.
-    summary->set_temp(1, Location::RegisterLocation(RDX));
-    summary->set_temp(2, Location::RequiresRegister());
+    // 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) {
@@ skipping 143 matching lines @@
       // No overflow check.
       __ orq(left, right);
       break;
     }
     case Token::kBIT_XOR: {
       // No overflow check.
       __ xorq(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.
       __ testq(right, right);
       __ j(ZERO, deopt);
       ASSERT(left == RAX);
       ASSERT((right != RDX) && (right != RAX));
-      ASSERT((temp != RDX) && (temp != RAX));
-      ASSERT(locs()->temp(1).reg() == RDX);
+      ASSERT(locs()->temp(0).reg() == RDX);
       ASSERT(result == RAX);
-      Register right_temp = locs()->temp(2).reg();
-      __ movq(right_temp, right);
       __ SmiUntag(left);
-      __ SmiUntag(right_temp);
+      __ SmiUntag(right);
       __ cqo();  // Sign extend RAX -> RDX:RAX.
-      __ idivq(right_temp);  //  RAX: quotient, RDX: remainder.
+      __ idivq(right);  //  RAX: quotient, RDX: remainder.
       // Check the corner case of dividing the 'MIN_SMI' with -1, in which
       // case we cannot tag the result.
       __ cmpq(result, Immediate(0x4000000000000000));
       __ j(EQUAL, deopt);
       __ SmiTag(result);
       break;
     }
     case Token::kSHR: {
       if (CanDeoptimize()) {
         __ cmpq(right, Immediate(0));
@@ skipping 955 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64