Reduce strength of ModI for power-of-2 divisor.

src/x64/lithium-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1329 matching lines @@
     ASSERT(instr->representation().IsTagged());
     return DoArithmeticT(Token::DIV, instr);
   }
 }
 
 
 LInstruction* LChunkBuilder::DoMod(HMod* instr) {
   if (instr->representation().IsInteger32()) {
     ASSERT(instr->left()->representation().IsInteger32());
     ASSERT(instr->right()->representation().IsInteger32());
-    // The temporary operand is necessary to ensure that right is not allocated
-    // into edx.
-    LOperand* temp = FixedTemp(rdx);
-    LOperand* value = UseFixed(instr->left(), rax);
-    LOperand* divisor = UseRegister(instr->right());
-    LModI* mod = new LModI(value, divisor, temp);
-    LInstruction* result = DefineFixed(mod, rdx);
+
+    LInstruction* result;
+    if (instr->HasPowerOf2Divisor()) {
+      ASSERT(!instr->CheckFlag(HValue::kCanBeDivByZero));
+      LOperand* value = UseRegisterAtStart(instr->left());
+      LModI* mod = new LModI(value, UseOrConstant(instr->right()), NULL);
+      result = DefineSameAsFirst(mod);
+    } else {
+      // The temporary operand is necessary to ensure that right is not allocated
+      // into edx.
+      LOperand* temp = FixedTemp(rdx);
+      LOperand* value = UseFixed(instr->left(), rax);
+      LOperand* divisor = UseRegister(instr->right());
+      LModI* mod = new LModI(value, divisor, temp);
+      result = DefineFixed(mod, rdx);
+    }
+
     return (instr->CheckFlag(HValue::kBailoutOnMinusZero) ||
             instr->CheckFlag(HValue::kCanBeDivByZero))
         ? AssignEnvironment(result)
         : result;
   } else if (instr->representation().IsTagged()) {
     return DoArithmeticT(Token::MOD, instr);
   } else {
     ASSERT(instr->representation().IsDouble());
     // We call a C function for double modulo. It can't trigger a GC.
     // We need to use fixed result register for the call.
@@ skipping 674 matching lines @@
 
 LInstruction* LChunkBuilder::DoLeaveInlined(HLeaveInlined* instr) {
   HEnvironment* outer = current_block_->last_environment()->outer();
   current_block_->UpdateEnvironment(outer);
   return NULL;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64