MIPS: Consistently use a separate Lithium instruction for flooring division.

Port r20395 (5b802048)

Original commit message:
Previously we tried to share some code on by a slightly confusing re-use
of LDivI for a (general) flooring division. Now we cleanly separate
concerns, just like for the rest of the division-like operations. Note
that ARM64 already did it this way.

If we really want to save some code, we can introduce some macro
assembler instructions and/or helper functions in the code generator in
a future CL, but we should really try to avoid being "clever" to save
just a few lines of trivial code. Effort != complexity. :-)

Renamed some related Lithium operands on the way for more consistency.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/220403009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20417 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -1242,26 +1242,27 @@ void LCodeGen::DoDivByConstI(LDivByConstI* instr) {
 }
 
 
+// TODO(svenpanne) Refactor this to avoid code duplication with DoFlooringDivI.
 void LCodeGen::DoDivI(LDivI* instr) {
   HBinaryOperation* hdiv = instr->hydrogen();
-  const Register left = ToRegister(instr->left());
-  const Register right = ToRegister(instr->right());
+  Register dividend = ToRegister(instr->dividend());
+  Register divisor = ToRegister(instr->divisor());
   const Register result = ToRegister(instr->result());
 
   // On MIPS div is asynchronous - it will run in the background while we
   // check for special cases.
-  __ div(left, right);
+  __ div(dividend, divisor);
 
   // Check for x / 0.
   if (hdiv->CheckFlag(HValue::kCanBeDivByZero)) {
-    DeoptimizeIf(eq, instr->environment(), right, Operand(zero_reg));
+    DeoptimizeIf(eq, instr->environment(), divisor, Operand(zero_reg));
   }
 
   // Check for (0 / -x) that will produce negative zero.
   if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero)) {
     Label left_not_zero;
-    __ Branch(&left_not_zero, ne, left, Operand(zero_reg));
-    DeoptimizeIf(lt, instr->environment(), right, Operand(zero_reg));
+    __ Branch(&left_not_zero, ne, dividend, Operand(zero_reg));
+    DeoptimizeIf(lt, instr->environment(), divisor, Operand(zero_reg));
     __ bind(&left_not_zero);
   }
 
@@ -1269,23 +1270,12 @@ void LCodeGen::DoDivI(LDivI* instr) {
   if (hdiv->CheckFlag(HValue::kCanOverflow) &&
       !hdiv->CheckFlag(HValue::kAllUsesTruncatingToInt32)) {
     Label left_not_min_int;
-    __ Branch(&left_not_min_int, ne, left, Operand(kMinInt));
-    DeoptimizeIf(eq, instr->environment(), right, Operand(-1));
+    __ Branch(&left_not_min_int, ne, dividend, Operand(kMinInt));
+    DeoptimizeIf(eq, instr->environment(), divisor, Operand(-1));
     __ bind(&left_not_min_int);
   }
 
-  if (hdiv->IsMathFloorOfDiv()) {
-    // We performed a truncating division. Correct the result if necessary.
-    Label done;
-    Register remainder = scratch0();
-    __ mfhi(remainder);
-    __ mflo(result);
-    __ Branch(&done, eq, remainder, Operand(zero_reg), USE_DELAY_SLOT);
-    __ Xor(remainder, remainder, Operand(right));
-    __ Branch(&done, ge, remainder, Operand(zero_reg));
-    __ Subu(result, result, Operand(1));
-    __ bind(&done);
-  } else if (!hdiv->CheckFlag(HValue::kAllUsesTruncatingToInt32)) {
+  if (!hdiv->CheckFlag(HValue::kAllUsesTruncatingToInt32)) {
     __ mfhi(result);
     DeoptimizeIf(ne, instr->environment(), result, Operand(zero_reg));
     __ mflo(result);
@@ -1398,6 +1388,52 @@ void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
 }
 
 
+// TODO(svenpanne) Refactor this to avoid code duplication with DoDivI.
+void LCodeGen::DoFlooringDivI(LFlooringDivI* instr) {
+  HBinaryOperation* hdiv = instr->hydrogen();
+  Register dividend = ToRegister(instr->dividend());
+  Register divisor = ToRegister(instr->divisor());
+  const Register result = ToRegister(instr->result());
+
+  // On MIPS div is asynchronous - it will run in the background while we
+  // check for special cases.
+  __ div(dividend, divisor);
+
+  // Check for x / 0.
+  if (hdiv->CheckFlag(HValue::kCanBeDivByZero)) {
+    DeoptimizeIf(eq, instr->environment(), divisor, Operand(zero_reg));
+  }
+
+  // Check for (0 / -x) that will produce negative zero.
+  if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero)) {
+    Label left_not_zero;
+    __ Branch(&left_not_zero, ne, dividend, Operand(zero_reg));
+    DeoptimizeIf(lt, instr->environment(), divisor, Operand(zero_reg));
+    __ bind(&left_not_zero);
+  }
+
+  // Check for (kMinInt / -1).
+  if (hdiv->CheckFlag(HValue::kCanOverflow) &&
+      !hdiv->CheckFlag(HValue::kAllUsesTruncatingToInt32)) {
+    Label left_not_min_int;
+    __ Branch(&left_not_min_int, ne, dividend, Operand(kMinInt));
+    DeoptimizeIf(eq, instr->environment(), divisor, Operand(-1));
+    __ bind(&left_not_min_int);
+  }
+
+  // We performed a truncating division. Correct the result if necessary.
+  Label done;
+  Register remainder = scratch0();
+  __ mfhi(remainder);
+  __ mflo(result);
+  __ Branch(&done, eq, remainder, Operand(zero_reg), USE_DELAY_SLOT);
+  __ Xor(remainder, remainder, Operand(divisor));
+  __ Branch(&done, ge, remainder, Operand(zero_reg));
+  __ Subu(result, result, Operand(1));
+  __ bind(&done);
+}
+
+
 void LCodeGen::DoMulI(LMulI* instr) {
   Register scratch = scratch0();
   Register result = ToRegister(instr->result());

src/mips/lithium-mips.cc

@@ -1295,7 +1295,7 @@ LInstruction* LChunkBuilder::DoDivByConstI(HDiv* instr) {
 }
 
 
-LInstruction* LChunkBuilder::DoDivI(HBinaryOperation* instr) {
+LInstruction* LChunkBuilder::DoDivI(HDiv* instr) {
   ASSERT(instr->representation().IsSmiOrInteger32());
   ASSERT(instr->left()->representation().Equals(instr->representation()));
   ASSERT(instr->right()->representation().Equals(instr->representation()));
@@ -1365,13 +1365,24 @@ LInstruction* LChunkBuilder::DoFlooringDivByConstI(HMathFloorOfDiv* instr) {
 }
 
 
+LInstruction* LChunkBuilder::DoFlooringDivI(HMathFloorOfDiv* 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());
+  LFlooringDivI* div = new(zone()) LFlooringDivI(dividend, divisor);
+  return AssignEnvironment(DefineAsRegister(div));
+}
+
+
 LInstruction* LChunkBuilder::DoMathFloorOfDiv(HMathFloorOfDiv* instr) {
   if (instr->RightIsPowerOf2()) {
     return DoFlooringDivByPowerOf2I(instr);
   } else if (instr->right()->IsConstant()) {
     return DoFlooringDivByConstI(instr);
   } else {
-    return DoDivI(instr);
+    return DoFlooringDivI(instr);
   }
 }
 

src/mips/lithium-mips.h

@@ -97,6 +97,7 @@ class LCodeGen;
   V(DummyUse)                                   \
   V(FlooringDivByConstI)                        \
   V(FlooringDivByPowerOf2I)                     \
+  V(FlooringDivI)                               \
   V(ForInCacheArray)                            \
   V(ForInPrepareMap)                            \
   V(FunctionLiteral)                            \
@@ -709,13 +710,13 @@ class LDivByConstI V8_FINAL : public LTemplateInstruction<1, 1, 0> {
 
 class LDivI V8_FINAL : public LTemplateInstruction<1, 2, 0> {
  public:
-  LDivI(LOperand* left, LOperand* right) {
-    inputs_[0] = left;
-    inputs_[1] = right;
+  LDivI(LOperand* dividend, LOperand* divisor) {
+    inputs_[0] = dividend;
+    inputs_[1] = divisor;
   }
 
-  LOperand* left() { return inputs_[0]; }
-  LOperand* right() { return inputs_[1]; }
+  LOperand* dividend() { return inputs_[0]; }
+  LOperand* divisor() { return inputs_[1]; }
 
   DECLARE_CONCRETE_INSTRUCTION(DivI, "div-i")
   DECLARE_HYDROGEN_ACCESSOR(BinaryOperation)
@@ -761,6 +762,21 @@ class LFlooringDivByConstI V8_FINAL : public LTemplateInstruction<1, 1, 2> {
 };
 
 
+class LFlooringDivI V8_FINAL : public LTemplateInstruction<1, 2, 0> {
+ public:
+  LFlooringDivI(LOperand* dividend, LOperand* divisor) {
+    inputs_[0] = dividend;
+    inputs_[1] = divisor;
+  }
+
+  LOperand* dividend() { return inputs_[0]; }
+  LOperand* divisor() { return inputs_[1]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(FlooringDivI, "flooring-div-i")
+  DECLARE_HYDROGEN_ACCESSOR(MathFloorOfDiv)
+};
+
+
 class LMulI V8_FINAL : public LTemplateInstruction<1, 2, 0> {
  public:
   LMulI(LOperand* left, LOperand* right) {
@@ -2679,12 +2695,13 @@ class LChunkBuilder V8_FINAL : public LChunkBuilderBase {
   LInstruction* DoMathClz32(HUnaryMathOperation* instr);
   LInstruction* DoDivByPowerOf2I(HDiv* instr);
   LInstruction* DoDivByConstI(HDiv* instr);
-  LInstruction* DoDivI(HBinaryOperation* instr);
+  LInstruction* DoDivI(HDiv* instr);
   LInstruction* DoModByPowerOf2I(HMod* instr);
   LInstruction* DoModByConstI(HMod* instr);
   LInstruction* DoModI(HMod* instr);
   LInstruction* DoFlooringDivByPowerOf2I(HMathFloorOfDiv* instr);
   LInstruction* DoFlooringDivByConstI(HMathFloorOfDiv* instr);
+  LInstruction* DoFlooringDivI(HMathFloorOfDiv* instr);
 
  private:
   enum Status {