Add support for unary plus in hydrogen compiler.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 28f4679a41cf5e7c37fc7545a0283bdceac37271..fceadd6fc761e775e25b0e989ac7581765fdf06a 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -875,7 +875,49 @@ void LCodeGen::DoMulI(LMulI* instr) {
   }
 
   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));
   }