MIPS: Improve integer multiplication.

src/mips/lithium-mips.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 1451 matching lines @@
   } else {
     return DoArithmeticT(Token::MOD, instr);
   }
 }
 
 
 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 {
+        if (bailout_on_minus_zero) {
+          left_op = UseRegister(left);
+        } else {
+          left_op = UseRegisterAtStart(left);
+        }
+        right_op = UseRegister(right);
+      }
     } else {
-      left = UseRegisterAtStart(instr->BetterLeftOperand());
+      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);
 
   } else if (instr->representation().IsDouble()) {
     if (kArchVariant == kMips32r2) {
       if (instr->UseCount() == 1 && instr->uses().value()->IsAdd()) {
         HAdd* add = HAdd::cast(instr->uses().value());
         if (instr == add->left()) {
           // This mul is the lhs of an add. The add and mul will be folded
@@ skipping 1008 matching lines @@
 
 
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseRegister(instr->index());
   return DefineAsRegister(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 
 } }  // namespace v8::internal