Handle non-power-of-2 divisors in division-like operations

src/arm/lithium-arm.cc

 // Copyright 2012 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 1239 matching lines @@
       (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::DoDivByConstI(HDiv* instr) {
+  ASSERT(instr->representation().IsInteger32());
+  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()) LDivByConstI(dividend, divisor));
+  bool can_deopt =
+      divisor == 0 ||
+      (instr->CheckFlag(HValue::kBailoutOnMinusZero) &&
+       instr->left()->RangeCanInclude(0) && divisor < 0) ||
+      !instr->CheckFlag(HInstruction::kAllUsesTruncatingToInt32);
+  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()) {
-    return instr->RightIsPowerOf2() ? DoDivByPowerOf2I(instr) : DoDivI(instr);
+    if (instr->RightIsPowerOf2()) {
+      return DoDivByPowerOf2I(instr);
+    } else if (instr->right()->IsConstant()) {
+      return DoDivByConstI(instr);
+    } else {
+      return DoDivI(instr);
+    }
   } else if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::DIV, instr);
   } else {
     return DoArithmeticT(Token::DIV, instr);
   }
 }
 
 
-bool LChunkBuilder::HasMagicNumberForDivisor(int32_t divisor) {
-  uint32_t divisor_abs = abs(divisor);
-  // 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:
-  // - Hacker's Delight, Henry S. Warren, Jr.
-  // - The PowerPC Compiler Writer’s Guide
-  // and probably many others.
-  //
-  // We handle
-  //   <divisor with magic numbers> * <power of 2>
-  // but not
-  //   <divisor with magic numbers> * <other divisor with magic numbers>
-  int32_t power_of_2_factor =
-    CompilerIntrinsics::CountTrailingZeros(divisor_abs);
-  DivMagicNumbers magic_numbers =
-    DivMagicNumberFor(divisor_abs >> power_of_2_factor);
-  return magic_numbers.M != InvalidDivMagicNumber.M;
-}
-
-
 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) {
+  ASSERT(instr->representation().IsInteger32());
+  ASSERT(instr->left()->representation().Equals(instr->representation()));
+  ASSERT(instr->right()->representation().Equals(instr->representation()));
   LOperand* dividend = UseRegister(instr->left());
-  LOperand* divisor = CpuFeatures::IsSupported(SUDIV)
-      ? UseRegister(instr->right())
-      : UseOrConstant(instr->right());
-  LOperand* remainder = TempRegister();
+  int32_t divisor = instr->right()->GetInteger32Constant();
   LInstruction* result =
-      DefineAsRegister(
-          new(zone()) LFlooringDivByConstI(dividend, divisor, remainder));
-  return AssignEnvironment(result);
+      DefineAsRegister(new(zone()) LFlooringDivByConstI(dividend, divisor));
+  bool can_deopt =
+      divisor == 0 ||
+      (instr->CheckFlag(HValue::kBailoutOnMinusZero) &&
+       instr->left()->RangeCanInclude(0) && divisor < 0);
+  return can_deopt ? AssignEnvironment(result) : 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);
+    return DoFlooringDivByConstI(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::DoModByConstI(HMod* 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()) LModByConstI(dividend, divisor));
+  bool can_deopt =
+      divisor == 0 ||
+      (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() ||
@@ skipping 15 matching lines @@
                       (instr->left()->CanBeNegative() &&
                        instr->CanBeZero() &&
                        instr->CheckFlag(HValue::kBailoutOnMinusZero)));
     return can_deopt ? AssignEnvironment(result) : result;
   }
 }
 
 
 LInstruction* LChunkBuilder::DoMod(HMod* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
-    return instr->RightIsPowerOf2() ? DoModByPowerOf2I(instr) : DoModI(instr);
+    if (instr->RightIsPowerOf2()) {
+      return DoModByPowerOf2I(instr);
+    } else if (instr->right()->IsConstant()) {
+      return DoModByConstI(instr);
+    } else {
+      return DoModI(instr);
+    }
   } else if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::MOD, instr);
   } else {
     return DoArithmeticT(Token::MOD, instr);
   }
 }
 
 
 LInstruction* LChunkBuilder::DoMul(HMul* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
@@ skipping 1111 matching lines @@
 }
 
 
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseRegister(instr->index());
   return DefineAsRegister(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 } }  // namespace v8::internal