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

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index c5b0c1dfae9c209507cfba7059a532f67cbd86a1..fb7c103a908cdcaaca468dddf48ee0720e4a9ffa 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1350,10 +1350,21 @@ LInstruction* LChunkBuilder::DoMod(HMod* instr) {
     // 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);