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

src/ia32/lithium-codegen-ia32.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 1383 matching lines @@
     }
     __ jmp(&done, Label::kNear);
   }
 
   __ bind(&dividend_is_not_negative);
   __ and_(dividend, mask);
   __ bind(&done);
 }
 
 
+void LCodeGen::DoModByConstI(LModByConstI* instr) {
+  Register dividend = ToRegister(instr->dividend());
+  int32_t divisor = instr->divisor();
+  ASSERT(ToRegister(instr->result()).is(eax));
+
+  if (divisor == 0) {
+    DeoptimizeIf(no_condition, instr->environment());
+    return;
+  }
+
+  __ FlooringDiv(dividend, Abs(divisor));
+  __ imul(edx, edx, Abs(divisor));
+  __ mov(eax, dividend);
+  __ sub(eax, edx);
+
+  // Check for negative zero.
+  HMod* hmod = instr->hydrogen();
+  if (hmod->CheckFlag(HValue::kBailoutOnMinusZero) &&
+      hmod->left()->CanBeNegative()) {
+    Label remainder_not_zero;
+    __ j(not_zero, &remainder_not_zero, Label::kNear);
+    __ cmp(dividend, Immediate(0));
+    DeoptimizeIf(less, instr->environment());
+    __ bind(&remainder_not_zero);
+  }
+}
+
+
 void LCodeGen::DoModI(LModI* instr) {
   HMod* hmod = instr->hydrogen();
   HValue* left = hmod->left();
   HValue* right = hmod->right();
 
   Register left_reg = ToRegister(instr->left());
   ASSERT(left_reg.is(eax));
   Register right_reg = ToRegister(instr->right());
   ASSERT(!right_reg.is(eax));
   ASSERT(!right_reg.is(edx));
@@ skipping 79 matching lines @@
     // The arithmetic shift is always OK, the 'if' is an optimization only.
     if (shift > 1) __ sar(result, 31);
     __ shr(result, 32 - shift);
     __ add(result, dividend);
     __ sar(result, shift);
   }
   if (divisor < 0) __ neg(result);
 }
 
 
+void LCodeGen::DoDivByConstI(LDivByConstI* instr) {
+  Register dividend = ToRegister(instr->dividend());
+  int32_t divisor = instr->divisor();
+  ASSERT(ToRegister(instr->result()).is(edx));
+
+  if (divisor == 0) {
+    DeoptimizeIf(no_condition, instr->environment());
+    return;
+  }
+
+  // Check for (0 / -x) that will produce negative zero.
+  HDiv* hdiv = instr->hydrogen();
+  if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero) &&
+      hdiv->left()->RangeCanInclude(0) && divisor < 0) {
+    __ test(dividend, dividend);
+    DeoptimizeIf(zero, instr->environment());
+  }
+
+  __ FlooringDiv(dividend, Abs(divisor));
+  if (divisor < 0) __ neg(edx);
+
+  if (!hdiv->CheckFlag(HInstruction::kAllUsesTruncatingToInt32)) {
+    __ mov(eax, edx);
+    __ imul(eax, eax, divisor);
+    __ sub(eax, dividend);
+    DeoptimizeIf(not_equal, instr->environment());
+  }
+}
+
+
 void LCodeGen::DoDivI(LDivI* instr) {
   Register dividend = ToRegister(instr->left());
   Register divisor = ToRegister(instr->right());
   Register remainder = ToRegister(instr->temp());
   Register result = ToRegister(instr->result());
   ASSERT(dividend.is(eax));
   ASSERT(remainder.is(edx));
   ASSERT(result.is(eax));
   ASSERT(!divisor.is(eax));
   ASSERT(!divisor.is(edx));
@@ skipping 79 matching lines @@
   }
   __ bind(&not_kmin_int);
   __ sar(dividend, shift);
   __ bind(&done);
 }
 
 
 void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
   Register dividend = ToRegister(instr->dividend());
   int32_t divisor = instr->divisor();
-  Register scratch = ToRegister(instr->temp());
-  ASSERT(ToRegister(instr->dividend()).is(eax));
   ASSERT(ToRegister(instr->result()).is(edx));
 
   if (divisor == 0) {
     DeoptimizeIf(no_condition, instr->environment());
     return;
   }
 
-  // Find b which: 2^b < divisor_abs < 2^(b+1).
-  uint32_t divisor_abs = abs(divisor);
-  unsigned b = 31 - CompilerIntrinsics::CountLeadingZeros(divisor_abs);
-  unsigned shift = 32 + b;  // Precision +1bit (effectively).
-  double multiplier_f =
-      static_cast<double>(static_cast<uint64_t>(1) << shift) / divisor_abs;
-  int64_t multiplier;
-  if (multiplier_f - std::floor(multiplier_f) < 0.5) {
-    multiplier = static_cast<int64_t>(std::floor(multiplier_f));
-  } else {
-    multiplier = static_cast<int64_t>(std::floor(multiplier_f)) + 1;
-  }
-  // The multiplier is a uint32.
-  ASSERT(multiplier > 0 &&
-         multiplier < (static_cast<int64_t>(1) << 32));
-  __ mov(scratch, dividend);
-  if (divisor < 0 &&
-      instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+  // Check for (0 / -x) that will produce negative zero.
+  HMathFloorOfDiv* hdiv = instr->hydrogen();
+  if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero) &&
+      hdiv->left()->RangeCanInclude(0) && divisor < 0) {
     __ test(dividend, dividend);
     DeoptimizeIf(zero, instr->environment());
   }
-  __ mov(edx, static_cast<int32_t>(multiplier));
-  __ imul(edx);
-  if (static_cast<int32_t>(multiplier) < 0) {
-    __ add(edx, scratch);
-  }
-  Register reg_lo = eax;
-  Register reg_byte_scratch = scratch;
-  if (!reg_byte_scratch.is_byte_register()) {
-    __ xchg(reg_lo, reg_byte_scratch);
-    reg_lo = scratch;
-    reg_byte_scratch = eax;
-  }
-  if (divisor < 0) {
-    __ xor_(reg_byte_scratch, reg_byte_scratch);
-    __ cmp(reg_lo, 0x40000000);
-    __ setcc(above, reg_byte_scratch);
-    __ neg(edx);
-    __ sub(edx, reg_byte_scratch);
-  } else {
-    __ xor_(reg_byte_scratch, reg_byte_scratch);
-    __ cmp(reg_lo, 0xC0000000);
-    __ setcc(above_equal, reg_byte_scratch);
-    __ add(edx, reg_byte_scratch);
-  }
-  __ sar(edx, shift - 32);
+
+  __ FlooringDiv(dividend, divisor);
 }
 
 
 void LCodeGen::DoMulI(LMulI* instr) {
   Register left = ToRegister(instr->left());
   LOperand* right = instr->right();
 
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     __ mov(ToRegister(instr->temp()), left);
   }
@@ skipping 4622 matching lines @@
                               FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32