Revert "Handle non-power-of-2 divisors in division-like operations", "A64 tweaks for division-like …

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index f530a183297f5f3af9d5cc9ae5cb7b1debc2366b..5e84347e1283ce46d634d8fdaddb79867c46fe8e 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1016,34 +1016,6 @@ void LCodeGen::DoModByPowerOf2I(LModByPowerOf2I* instr) {
 }
 
 
-void LCodeGen::DoModByConstI(LModByConstI* instr) {
-  Register dividend = ToRegister(instr->dividend());
-  int32_t divisor = instr->divisor();
-  ASSERT(ToRegister(instr->result()).is(rax));
-
-  if (divisor == 0) {
-    DeoptimizeIf(no_condition, instr->environment());
-    return;
-  }
-
-  __ FlooringDiv(dividend, Abs(divisor));
-  __ imull(rdx, rdx, Immediate(Abs(divisor)));
-  __ movl(rax, dividend);
-  __ subl(rax, rdx);
-
-  // 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);
-    __ cmpl(dividend, Immediate(0));
-    DeoptimizeIf(less, instr->environment());
-    __ bind(&remainder_not_zero);
-  }
-}
-
-
 void LCodeGen::DoModI(LModI* instr) {
   if (instr->hydrogen()->RightIsPowerOf2()) {
     return DoModByPowerOf2I(reinterpret_cast<LModByPowerOf2I*>(instr));
@@ -1147,22 +1119,42 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
 void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
   Register dividend = ToRegister(instr->dividend());
   int32_t divisor = instr->divisor();
-  ASSERT(ToRegister(instr->result()).is(rdx));
+  Register temp = ToRegister(instr->temp());
+  Register result = ToRegister(instr->result());
 
   if (divisor == 0) {
     DeoptimizeIf(no_condition, instr->environment());
     return;
   }
 
-  // Check for (0 / -x) that will produce negative zero.
-  HMathFloorOfDiv* hdiv = instr->hydrogen();
-  if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero) &&
-      hdiv->left()->RangeCanInclude(0) && divisor < 0) {
-    __ testl(dividend, dividend);
+  // 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));
+  // The multiply is int64, so sign-extend to r64.
+  __ movsxlq(temp, dividend);
+  if (divisor < 0 &&
+      instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+    __ neg(temp);
     DeoptimizeIf(zero, instr->environment());
   }
+  __ Set(result, multiplier);
+  // Result just fit in r64, because it's int32 * uint32.
+  __ imul(result, temp);
 
-  __ FlooringDiv(dividend, divisor);
+  __ addq(result, Immediate(1 << 30));
+  __ sar(result, Immediate(shift));
 }
 
 
@@ -1206,36 +1198,6 @@ void LCodeGen::DoDivByPowerOf2I(LDivByPowerOf2I* instr) {
 }
 
 
-void LCodeGen::DoDivByConstI(LDivByConstI* instr) {
-  Register dividend = ToRegister(instr->dividend());
-  int32_t divisor = instr->divisor();
-  ASSERT(ToRegister(instr->result()).is(rdx));
-
-  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) {
-    __ testl(dividend, dividend);
-    DeoptimizeIf(zero, instr->environment());
-  }
-
-  __ FlooringDiv(dividend, Abs(divisor));
-  if (divisor < 0) __ neg(rdx);
-
-  if (!hdiv->CheckFlag(HInstruction::kAllUsesTruncatingToInt32)) {
-    __ movl(rax, rdx);
-    __ imull(rax, rax, Immediate(divisor));
-    __ subl(rax, dividend);
-    DeoptimizeIf(not_equal, instr->environment());
-  }
-}
-
-
 void LCodeGen::DoDivI(LDivI* instr) {
   Register dividend = ToRegister(instr->left());
   Register divisor = ToRegister(instr->right());