Add support for unary plus in hydrogen compiler.

src/ia32/lithium-codegen-ia32.cc

 // Copyright 2011 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 857 matching lines @@
 
 void LCodeGen::DoMulI(LMulI* instr) {
   Register left = ToRegister(instr->InputAt(0));
   LOperand* right = instr->InputAt(1);
 
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     __ mov(ToRegister(instr->TempAt(0)), left);
   }
 
   if (right->IsConstantOperand()) {
-    __ imul(left, left, ToInteger32(LConstantOperand::cast(right)));
+    // Try strength reductions on the multiplication.
+    // All replacement instructions are at most as long as the imul
+    // and have better latency.
+    int constant = ToInteger32(LConstantOperand::cast(right));
+    if (constant == -1) {
+      __ neg(left);
+    } else if (constant == 0) {
+      __ xor_(left, Operand(left));
+    } else if (constant == 2) {
+      __ add(left, Operand(left));
+    } else if (!instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
+      // If we know that the multiplication can't overflow, it's safe to
+      // use instructions that don't set the overflow flag for the
+      // multiplication.
+      switch (constant) {
+        case 1:
+          // Do nothing.
+          break;
+        case 3:
+          __ lea(left, Operand(left, left, times_2, 0));
+          break;
+        case 4:
+          __ shl(left, 2);
+          break;
+        case 5:
+          __ lea(left, Operand(left, left, times_4, 0));
+          break;
+        case 8:
+          __ shl(left, 3);
+          break;
+        case 9:
+          __ lea(left, Operand(left, left, times_8, 0));
+          break;
+       case 16:
+         __ shl(left, 4);
+         break;
+        default:
+          __ imul(left, left, constant);
+          break;
+      }
+    } else {
+      __ imul(left, left, constant);
+    }
   } else {
     __ imul(left, ToOperand(right));
   }
 
   if (instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
     DeoptimizeIf(overflow, instr->environment());
   }
 
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     // Bail out if the result is supposed to be negative zero.
@@ skipping 2981 matching lines @@
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32