MIPS: Improve integer multiplication.

Port r16576 (8ce78a4)

TEST=test/mjsunit/lithium/MulI.js
BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/25050002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16997 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -1403,11 +1403,11 @@ void LCodeGen::DoMulI(LMulI* instr) {
   Register left = ToRegister(instr->left());
   LOperand* right_op = instr->right();
 
-  bool can_overflow = instr->hydrogen()->CheckFlag(HValue::kCanOverflow);
   bool bailout_on_minus_zero =
     instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero);
+  bool overflow = instr->hydrogen()->CheckFlag(HValue::kCanOverflow);
 
-  if (right_op->IsConstantOperand() && !can_overflow) {
+  if (right_op->IsConstantOperand()) {
     int32_t constant = ToInteger32(LConstantOperand::cast(right_op));
 
     if (bailout_on_minus_zero && (constant < 0)) {
@@ -1418,7 +1418,12 @@ void LCodeGen::DoMulI(LMulI* instr) {
 
     switch (constant) {
       case -1:
+        if (overflow) {
+          __ SubuAndCheckForOverflow(result, zero_reg, left, scratch);
+          DeoptimizeIf(lt, instr->environment(), scratch, Operand(zero_reg));
+        } else {
           __ Subu(result, zero_reg, left);
+        }
         break;
       case 0:
         if (bailout_on_minus_zero) {
@@ -1439,27 +1444,23 @@ void LCodeGen::DoMulI(LMulI* instr) {
         int32_t mask = constant >> 31;
         uint32_t constant_abs = (constant + mask) ^ mask;
 
-        if (IsPowerOf2(constant_abs) ||
-            IsPowerOf2(constant_abs - 1) ||
-            IsPowerOf2(constant_abs + 1)) {
         if (IsPowerOf2(constant_abs)) {
           int32_t shift = WhichPowerOf2(constant_abs);
           __ sll(result, left, shift);
+          // Correct the sign of the result if the constant is negative.
+          if (constant < 0)  __ Subu(result, zero_reg, result);
         } else if (IsPowerOf2(constant_abs - 1)) {
           int32_t shift = WhichPowerOf2(constant_abs - 1);
           __ sll(scratch, left, shift);
           __ Addu(result, scratch, left);
+          // Correct the sign of the result if the constant is negative.
+          if (constant < 0)  __ Subu(result, zero_reg, result);
         } else if (IsPowerOf2(constant_abs + 1)) {
           int32_t shift = WhichPowerOf2(constant_abs + 1);
           __ sll(scratch, left, shift);
           __ Subu(result, scratch, left);
-          }
-
-          // Correct the sign of the result is the constant is negative.
-          if (constant < 0)  {
-            __ Subu(result, zero_reg, result);
-          }
-
+          // Correct the sign of the result if the constant is negative.
+          if (constant < 0)  __ Subu(result, zero_reg, result);
         } else {
           // Generate standard code.
           __ li(at, constant);
@@ -1468,12 +1469,10 @@ void LCodeGen::DoMulI(LMulI* instr) {
     }
 
   } else {
-    Register right = EmitLoadRegister(right_op, scratch);
-    if (bailout_on_minus_zero) {
-      __ Or(ToRegister(instr->temp()), left, right);
-    }
+    ASSERT(right_op->IsRegister());
+    Register right = ToRegister(right_op);
 
-    if (can_overflow) {
+    if (overflow) {
       // hi:lo = left * right.
       if (instr->hydrogen()->representation().IsSmi()) {
         __ SmiUntag(result, left);
@@ -1497,12 +1496,13 @@ void LCodeGen::DoMulI(LMulI* instr) {
     }
 
     if (bailout_on_minus_zero) {
-      // Bail out if the result is supposed to be negative zero.
       Label done;
-      __ Branch(&done, ne, result, Operand(zero_reg));
-      DeoptimizeIf(lt,
+      __ Xor(at, left, right);
+      __ Branch(&done, ge, at, Operand(zero_reg));
+      // Bail out if the result is minus zero.
+      DeoptimizeIf(eq,
                    instr->environment(),
-                   ToRegister(instr->temp()),
+                   result,
                    Operand(zero_reg));
       __ bind(&done);
     }

src/mips/lithium-mips.cc

@@ -1469,20 +1469,39 @@ LInstruction* LChunkBuilder::DoMul(HMul* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
     ASSERT(instr->left()->representation().Equals(instr->representation()));
     ASSERT(instr->right()->representation().Equals(instr->representation()));
-    LOperand* left;
-    LOperand* right = UseOrConstant(instr->BetterRightOperand());
-    LOperand* temp = NULL;
-    if (instr->CheckFlag(HValue::kBailoutOnMinusZero) &&
-        (instr->CheckFlag(HValue::kCanOverflow) ||
-        !right->IsConstantOperand())) {
-      left = UseRegister(instr->BetterLeftOperand());
-      temp = TempRegister();
+    HValue* left = instr->BetterLeftOperand();
+    HValue* right = instr->BetterRightOperand();
+    LOperand* left_op;
+    LOperand* right_op;
+    bool can_overflow = instr->CheckFlag(HValue::kCanOverflow);
+    bool bailout_on_minus_zero = instr->CheckFlag(HValue::kBailoutOnMinusZero);
+
+    if (right->IsConstant()) {
+      HConstant* constant = HConstant::cast(right);
+      int32_t constant_value = constant->Integer32Value();
+      // Constants -1, 0 and 1 can be optimized if the result can overflow.
+      // For other constants, it can be optimized only without overflow.
+      if (!can_overflow || ((constant_value >= -1) && (constant_value <= 1))) {
+        left_op = UseRegisterAtStart(left);
+        right_op = UseConstant(right);
       } else {
-      left = UseRegisterAtStart(instr->BetterLeftOperand());
+        if (bailout_on_minus_zero) {
+          left_op = UseRegister(left);
+        } else {
+          left_op = UseRegisterAtStart(left);
+        }
+        right_op = UseRegister(right);
+      }
+    } else {
+      if (bailout_on_minus_zero) {
+        left_op = UseRegister(left);
+      } else {
+        left_op = UseRegisterAtStart(left);
+      }
+      right_op = UseRegister(right);
     }
-    LMulI* mul = new(zone()) LMulI(left, right, temp);
-    if (instr->CheckFlag(HValue::kCanOverflow) ||
-        instr->CheckFlag(HValue::kBailoutOnMinusZero)) {
+    LMulI* mul = new(zone()) LMulI(left_op, right_op);
+    if (can_overflow || bailout_on_minus_zero) {
       AssignEnvironment(mul);
     }
     return DefineAsRegister(mul);

src/mips/lithium-mips.h

@@ -688,17 +688,15 @@ class LMathFloorOfDiv V8_FINAL : public LTemplateInstruction<1, 2, 1> {
 };
 
 
-class LMulI V8_FINAL : public LTemplateInstruction<1, 2, 1> {
+class LMulI V8_FINAL : public LTemplateInstruction<1, 2, 0> {
  public:
-  LMulI(LOperand* left, LOperand* right, LOperand* temp) {
+  LMulI(LOperand* left, LOperand* right) {
     inputs_[0] = left;
     inputs_[1] = right;
-    temps_[0] = temp;
   }
 
   LOperand* left() { return inputs_[0]; }
   LOperand* right() { return inputs_[1]; }
-  LOperand* temp() { return temps_[0]; }
 
   DECLARE_CONCRETE_INSTRUCTION(MulI, "mul-i")
   DECLARE_HYDROGEN_ACCESSOR(Mul)