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

src/arm/lithium-arm.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 1332 matching lines @@
 
 LInstruction* LChunkBuilder::DoMod(HMod* instr) {
   if (instr->representation().IsInteger32()) {
     // TODO(1042) The fixed register allocation
     // is needed because we call GenericBinaryOpStub from
     // the generated code, which requires registers r0
     // and r1 to be used. We should remove that
     // when we provide a native implementation.
     ASSERT(instr->left()->representation().IsInteger32());
     ASSERT(instr->right()->representation().IsInteger32());
-    LOperand* value = UseFixed(instr->left(), r0);
-    LOperand* divisor = UseFixed(instr->right(), r1);
-    LInstruction* result = DefineFixed(new LModI(value, divisor), r0);
-    result = AssignEnvironment(AssignPointerMap(result));
+
+    LInstruction* result;
+    if (instr->HasPowerOf2Divisor()) {
+      ASSERT(!instr->CheckFlag(HValue::kCanBeDivByZero));
+      LOperand* value = UseRegisterAtStart(instr->left());
+      LModI* mod = new LModI(value, UseOrConstant(instr->right()));
+      result = DefineSameAsFirst(mod);
+      result = AssignEnvironment(result);
+    } else {
+      LOperand* value = UseFixed(instr->left(), r0);
+      LOperand* divisor = UseFixed(instr->right(), r1);
+      result = DefineFixed(new LModI(value, divisor), r0);
+      result = AssignEnvironment(AssignPointerMap(result));
+    }
+
     return 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.
     // TODO(fschneider): Allow any register as input registers.
     LOperand* left = UseFixedDouble(instr->left(), d1);
     LOperand* right = UseFixedDouble(instr->right(), d2);
@@ skipping 671 matching lines @@
 
 
 LInstruction* LChunkBuilder::DoLeaveInlined(HLeaveInlined* instr) {
   HEnvironment* outer = current_block_->last_environment()->outer();
   current_block_->UpdateEnvironment(outer);
   return NULL;
 }
 
 
 } }  // namespace v8::internal