Consistenly handle power-of-2 divisors in division-like operations

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 14c7b08fa7c1a928c3e07491178039c4078c02aa..c5e6b0486734e3537fdd41f4a9d0eac2c9cabb6c 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1238,21 +1238,40 @@ LInstruction* LChunkBuilder::DoBitwise(HBitwise* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoDivByPowerOf2I(HDiv* instr) {
+  ASSERT(instr->representation().IsSmiOrInteger32());
+  ASSERT(instr->left()->representation().Equals(instr->representation()));
+  ASSERT(instr->right()->representation().Equals(instr->representation()));
+  LOperand* dividend = UseRegister(instr->left());
+  int32_t divisor = instr->right()->GetInteger32Constant();
+  LInstruction* result =
+      DefineAsRegister(new(zone()) LDivByPowerOf2I(dividend, divisor));
+  bool can_deopt =
+      (instr->CheckFlag(HValue::kBailoutOnMinusZero) &&
+       instr->left()->RangeCanInclude(0) && divisor < 0) ||
+      (instr->CheckFlag(HValue::kCanOverflow) &&
+       instr->left()->RangeCanInclude(kMinInt) && divisor == -1) ||
+      (!instr->CheckFlag(HInstruction::kAllUsesTruncatingToInt32) &&
+       divisor != 1 && divisor != -1);
+  return can_deopt ? AssignEnvironment(result) : result;
+}
+
+
+LInstruction* LChunkBuilder::DoDivI(HBinaryOperation* instr) {
+  ASSERT(instr->representation().IsSmiOrInteger32());
+  ASSERT(instr->left()->representation().Equals(instr->representation()));
+  ASSERT(instr->right()->representation().Equals(instr->representation()));
+  LOperand* dividend = UseRegister(instr->left());
+  LOperand* divisor = UseRegister(instr->right());
+  LOperand* temp = CpuFeatures::IsSupported(SUDIV) ? NULL : FixedTemp(d4);
+  LDivI* div = new(zone()) LDivI(dividend, divisor, temp);
+  return AssignEnvironment(DefineAsRegister(div));
+}
+
+
 LInstruction* LChunkBuilder::DoDiv(HDiv* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
-    ASSERT(instr->left()->representation().Equals(instr->representation()));
-    ASSERT(instr->right()->representation().Equals(instr->representation()));
-    if (instr->RightIsPowerOf2()) {
-      ASSERT(!instr->CheckFlag(HValue::kCanBeDivByZero));
-      LOperand* value = UseRegister(instr->left());
-      LDivI* div = new(zone()) LDivI(value, UseConstant(instr->right()), NULL);
-      return AssignEnvironment(DefineAsRegister(div));
-    }
-    LOperand* dividend = UseRegister(instr->left());
-    LOperand* divisor = UseRegister(instr->right());
-    LOperand* temp = CpuFeatures::IsSupported(SUDIV) ? NULL : FixedTemp(d4);
-    LDivI* div = new(zone()) LDivI(dividend, divisor, temp);
-    return AssignEnvironment(DefineAsRegister(div));
+    return instr->RightIsPowerOf2() ? DoDivByPowerOf2I(instr) : DoDivI(instr);
   } else if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::DIV, instr);
   } else {
@@ -1263,10 +1282,8 @@ LInstruction* LChunkBuilder::DoDiv(HDiv* instr) {
 
 bool LChunkBuilder::HasMagicNumberForDivisor(int32_t divisor) {
   uint32_t divisor_abs = abs(divisor);
-  // Dividing by 0, 1, and powers of 2 is easy.
-  // Note that IsPowerOf2(0) returns true;
-  ASSERT(IsPowerOf2(0) == true);
-  if (IsPowerOf2(divisor_abs)) return true;
+  // Dividing by 0 or powers of 2 is easy.
+  if (divisor == 0 || IsPowerOf2(divisor_abs)) return true;
 
   // We have magic numbers for a few specific divisors.
   // Details and proofs can be found in:
@@ -1282,77 +1299,103 @@ bool LChunkBuilder::HasMagicNumberForDivisor(int32_t divisor) {
     CompilerIntrinsics::CountTrailingZeros(divisor_abs);
   DivMagicNumbers magic_numbers =
     DivMagicNumberFor(divisor_abs >> power_of_2_factor);
-  if (magic_numbers.M != InvalidDivMagicNumber.M) return true;
-
-  return false;
+  return magic_numbers.M != InvalidDivMagicNumber.M;
 }
 
 
-LInstruction* LChunkBuilder::DoMathFloorOfDiv(HMathFloorOfDiv* instr) {
-  // LMathFloorOfDiv  can only handle  a subset  of divisors, so fall
-  // back to a flooring division in all other cases.
-  HValue* right = instr->right();
-  if (!right->IsInteger32Constant() ||
-      (!CpuFeatures::IsSupported(SUDIV) &&
-       !HasMagicNumberForDivisor(HConstant::cast(right)->Integer32Value()))) {
-    LOperand* dividend = UseRegister(instr->left());
-    LOperand* divisor = UseRegister(right);
-    LOperand* temp = CpuFeatures::IsSupported(SUDIV) ? NULL : FixedTemp(d4);
-    LDivI* div = new(zone()) LDivI(dividend, divisor, temp);
-    return AssignEnvironment(DefineAsRegister(div));
-  }
+LInstruction* LChunkBuilder::DoFlooringDivByPowerOf2I(HMathFloorOfDiv* instr) {
+  LOperand* dividend = UseRegisterAtStart(instr->left());
+  int32_t divisor = instr->right()->GetInteger32Constant();
+  LInstruction* result =
+      DefineSameAsFirst(
+          new(zone()) LFlooringDivByPowerOf2I(dividend, divisor));
+  bool can_deopt =
+      (instr->CheckFlag(HValue::kBailoutOnMinusZero) && divisor < 0) ||
+      (instr->left()->RangeCanInclude(kMinInt) && divisor == -1);
+  return can_deopt ? AssignEnvironment(result) : result;
+}
+
 
+LInstruction* LChunkBuilder::DoFlooringDivByConstI(HMathFloorOfDiv* instr) {
   LOperand* dividend = UseRegister(instr->left());
   LOperand* divisor = CpuFeatures::IsSupported(SUDIV)
-      ? UseRegister(right)
-      : UseOrConstant(right);
+      ? UseRegister(instr->right())
+      : UseOrConstant(instr->right());
   LOperand* remainder = TempRegister();
-  return AssignEnvironment(DefineAsRegister(
-          new(zone()) LMathFloorOfDiv(dividend, divisor, remainder)));
+  LInstruction* result =
+      DefineAsRegister(
+          new(zone()) LFlooringDivByConstI(dividend, divisor, remainder));
+  return AssignEnvironment(result);
+}
+
+
+LInstruction* LChunkBuilder::DoMathFloorOfDiv(HMathFloorOfDiv* instr) {
+  if (instr->RightIsPowerOf2()) {
+    return DoFlooringDivByPowerOf2I(instr);
+  } else if (instr->right()->IsConstant()) {
+    // LMathFloorOfDiv can currently only handle a subset of divisors, so fall
+    // back to a flooring division in all other cases.
+    return (CpuFeatures::IsSupported(SUDIV) ||
+            HasMagicNumberForDivisor(instr->right()->GetInteger32Constant()))
+        ? DoFlooringDivByConstI(instr)
+        : DoDivI(instr);
+  } else {
+    return DoDivI(instr);
+  }
+}
+
+
+LInstruction* LChunkBuilder::DoModByPowerOf2I(HMod* instr) {
+  ASSERT(instr->representation().IsSmiOrInteger32());
+  ASSERT(instr->left()->representation().Equals(instr->representation()));
+  ASSERT(instr->right()->representation().Equals(instr->representation()));
+  LOperand* dividend = UseRegisterAtStart(instr->left());
+  int32_t divisor = instr->right()->GetInteger32Constant();
+  LInstruction* result =
+      DefineSameAsFirst(new(zone()) LModByPowerOf2I(dividend, divisor));
+  bool can_deopt =
+      instr->CheckFlag(HValue::kBailoutOnMinusZero) &&
+      instr->left()->CanBeNegative();
+  return can_deopt ? AssignEnvironment(result) : result;
+}
+
+
+LInstruction* LChunkBuilder::DoModI(HMod* instr) {
+  ASSERT(instr->representation().IsSmiOrInteger32());
+  ASSERT(instr->left()->representation().Equals(instr->representation()));
+  ASSERT(instr->right()->representation().Equals(instr->representation()));
+  if (CpuFeatures::IsSupported(SUDIV)) {
+    LOperand* dividend = UseRegister(instr->left());
+    LOperand* divisor = UseRegister(instr->right());
+    LInstruction* result =
+        DefineAsRegister(new(zone()) LModI(dividend, divisor, NULL, NULL));
+    bool can_deopt = (instr->right()->CanBeZero() ||
+                      (instr->left()->RangeCanInclude(kMinInt) &&
+                       instr->right()->RangeCanInclude(-1) &&
+                       instr->CheckFlag(HValue::kBailoutOnMinusZero)) ||
+                      (instr->left()->CanBeNegative() &&
+                       instr->CanBeZero() &&
+                       instr->CheckFlag(HValue::kBailoutOnMinusZero)));
+    return can_deopt ? AssignEnvironment(result) : result;
+  } else {
+    LOperand* dividend = UseRegister(instr->left());
+    LOperand* divisor = UseRegister(instr->right());
+    LOperand* temp = FixedTemp(d10);
+    LOperand* temp2 = FixedTemp(d11);
+    LInstruction* result =
+        DefineAsRegister(new(zone()) LModI(dividend, divisor, temp, temp2));
+    bool can_deopt = (instr->right()->CanBeZero() ||
+                      (instr->left()->CanBeNegative() &&
+                       instr->CanBeZero() &&
+                       instr->CheckFlag(HValue::kBailoutOnMinusZero)));
+    return can_deopt ? AssignEnvironment(result) : result;
+  }
 }
 
 
 LInstruction* LChunkBuilder::DoMod(HMod* instr) {
-  HValue* left = instr->left();
-  HValue* right = instr->right();
   if (instr->representation().IsSmiOrInteger32()) {
-    ASSERT(instr->left()->representation().Equals(instr->representation()));
-    ASSERT(instr->right()->representation().Equals(instr->representation()));
-    if (instr->RightIsPowerOf2()) {
-      ASSERT(!right->CanBeZero());
-      LModI* mod = new(zone()) LModI(UseRegisterAtStart(left),
-                                     UseConstant(right));
-      LInstruction* result = DefineAsRegister(mod);
-      return (left->CanBeNegative() &&
-              instr->CheckFlag(HValue::kBailoutOnMinusZero))
-          ? AssignEnvironment(result)
-          : result;
-    } else if (CpuFeatures::IsSupported(SUDIV)) {
-      LModI* mod = new(zone()) LModI(UseRegister(left),
-                                     UseRegister(right));
-      LInstruction* result = DefineAsRegister(mod);
-      return (right->CanBeZero() ||
-              (left->RangeCanInclude(kMinInt) &&
-               right->RangeCanInclude(-1) &&
-               instr->CheckFlag(HValue::kBailoutOnMinusZero)) ||
-              (left->CanBeNegative() &&
-               instr->CanBeZero() &&
-               instr->CheckFlag(HValue::kBailoutOnMinusZero)))
-          ? AssignEnvironment(result)
-          : result;
-    } else {
-      LModI* mod = new(zone()) LModI(UseRegister(left),
-                                     UseRegister(right),
-                                     FixedTemp(d10),
-                                     FixedTemp(d11));
-      LInstruction* result = DefineAsRegister(mod);
-      return (right->CanBeZero() ||
-              (left->CanBeNegative() &&
-               instr->CanBeZero() &&
-               instr->CheckFlag(HValue::kBailoutOnMinusZero)))
-          ? AssignEnvironment(result)
-          : result;
-    }
+    return instr->RightIsPowerOf2() ? DoModByPowerOf2I(instr) : DoModI(instr);
   } else if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::MOD, instr);
   } else {