MIPS: Improve integer multiplication.

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index c8691847aca0035bf9d18caaf9b9949d8c5d4c86..97dcd163cf2c7a6b2ffaf0e37e3feacf31db8c29 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/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:
-        __ Subu(result, zero_reg, left);
+        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);
-          } else if (IsPowerOf2(constant_abs - 1)) {
-            int32_t shift = WhichPowerOf2(constant_abs - 1);
-            __ sll(scratch, left, shift);
-            __ Addu(result, scratch, left);
-          } 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);
-          }
-
+        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 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);
     }