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

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 28f4679a41cf5e7c37fc7545a0283bdceac37271..e2b7c379937af0ef2c3e409ef6ceac0fa208d891 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -781,41 +781,65 @@ void LCodeGen::DoUnknownOSRValue(LUnknownOSRValue* instr) {
 
 
 void LCodeGen::DoModI(LModI* instr) {
-  LOperand* right = instr->InputAt(1);
-  ASSERT(ToRegister(instr->result()).is(edx));
-  ASSERT(ToRegister(instr->InputAt(0)).is(eax));
-  ASSERT(!ToRegister(instr->InputAt(1)).is(eax));
-  ASSERT(!ToRegister(instr->InputAt(1)).is(edx));
+  if (HMod::cast(instr->hydrogen())->HasPowerOf2Divisor()) {
+    Register dividend = ToRegister(instr->InputAt(0));
 
-  Register right_reg = ToRegister(right);
+    int32_t divisor =
+        HConstant::cast(
+            HMod::cast(instr->hydrogen())->right())->Integer32Value();
 
-  // Check for x % 0.
-  if (instr->hydrogen()->CheckFlag(HValue::kCanBeDivByZero)) {
-    __ test(right_reg, ToOperand(right));
-    DeoptimizeIf(zero, instr->environment());
-  }
+    if (divisor < 0) divisor = -divisor;
 
-  // Sign extend to edx.
-  __ cdq();
+    NearLabel positive_dividend, done;
+    __ test(dividend, Operand(dividend));
+    __ j(not_sign, &positive_dividend);
+    __ neg(dividend);
+    __ and_(dividend, divisor - 1);
+    __ neg(dividend);
+    if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+      __ j(not_zero, &done);
+      DeoptimizeIf(no_condition, instr->environment());
+    }
+    __ bind(&positive_dividend);
+    __ and_(dividend, divisor - 1);
+    __ bind(&done);
+  } else {
+    LOperand* right = instr->InputAt(1);
+    ASSERT(ToRegister(instr->InputAt(0)).is(eax));
+    ASSERT(ToRegister(instr->result()).is(edx));
 
-  // Check for (0 % -x) that will produce negative zero.
-  if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
-    NearLabel positive_left;
-    NearLabel done;
-    __ test(eax, Operand(eax));
-    __ j(not_sign, &positive_left);
-    __ idiv(right_reg);
+    Register right_reg = ToRegister(right);
+    ASSERT(!right_reg.is(eax));
+    ASSERT(!right_reg.is(edx));
 
-    // Test the remainder for 0, because then the result would be -0.
-    __ test(edx, Operand(edx));
-    __ j(not_zero, &done);
+    // Check for x % 0.
+    if (instr->hydrogen()->CheckFlag(HValue::kCanBeDivByZero)) {
+      __ test(right_reg, ToOperand(right));
+      DeoptimizeIf(zero, instr->environment());
+    }
 
-    DeoptimizeIf(no_condition, instr->environment());
-    __ bind(&positive_left);
-    __ idiv(right_reg);
-    __ bind(&done);
-  } else {
-    __ idiv(right_reg);
+    // Sign extend to edx.
+    __ cdq();
+
+    // Check for (0 % -x) that will produce negative zero.
+    if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+      NearLabel positive_left;
+      NearLabel done;
+      __ test(eax, Operand(eax));
+      __ j(not_sign, &positive_left);
+      __ idiv(right_reg);
+
+      // Test the remainder for 0, because then the result would be -0.
+      __ test(edx, Operand(edx));
+      __ j(not_zero, &done);
+
+      DeoptimizeIf(no_condition, instr->environment());
+      __ bind(&positive_left);
+      __ idiv(right_reg);
+      __ bind(&done);
+    } else {
+      __ idiv(right_reg);
+    }
   }
 }