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

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 8dd35b6b8394251c79842b7a56e4097d82b5cd5b..e188f8136689a5737173ebb573617ceda287e727 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -796,6 +796,31 @@ void LCodeGen::DoUnknownOSRValue(LUnknownOSRValue* instr) {
 
 
 void LCodeGen::DoModI(LModI* instr) {
+  if (HMod::cast(instr->hydrogen())->HasPowerOf2Divisor()) {

[Kevin Millikin (Chromium), 2011/03/14 14:35:07]

The HMod::cast should not be necessary here (and just below).

+    Register dividend = ToRegister(instr->InputAt(0));
+
+    int32_t divisor =
+        HConstant::cast(
+            HMod::cast(instr->hydrogen())->right())->Integer32Value();
+
+    if (divisor < 0) divisor = -divisor;
+
+    Label positive_dividend, done;
+    __ tst(dividend, Operand(dividend));
+    __ b(pl, &positive_dividend);
+    __ rsb(dividend, dividend, Operand(0));
+    __ and_(dividend, dividend, Operand(divisor - 1));
+    __ rsb(dividend, dividend, Operand(0), SetCC);
+    if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+      __ b(ne, &done);
+      DeoptimizeIf(al, instr->environment());
+    }
+    __ bind(&positive_dividend);
+    __ and_(dividend, dividend, Operand(divisor - 1));
+    __ bind(&done);
+    return;
+  }
+
   class DeferredModI: public LDeferredCode {
    public:
     DeferredModI(LCodeGen* codegen, LModI* instr)
@@ -856,6 +881,7 @@ void LCodeGen::DoModI(LModI* instr) {
   __ JumpIfNotPowerOfTwoOrZero(right, scratch, &call_stub);
   // Perform modulo operation (scratch contains right - 1).
   __ and_(result, scratch, Operand(left));
+  __ b(&done);
 
   __ bind(&call_stub);
   // Call the stub. The numbers in r0 and r1 have