Replace log2 with MostSignificantBit

src/hydrogen-instructions.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 2310 matching lines @@
       int64_t left_upper = left()->range()->upper();
       int64_t left_lower = left()->range()->lower();
       int64_t right_upper = right()->range()->upper();
       int64_t right_lower = right()->range()->lower();
 
       if (left_upper < 0) left_upper = ~left_upper;
       if (left_lower < 0) left_lower = ~left_lower;
       if (right_upper < 0) right_upper = ~right_upper;
       if (right_lower < 0) right_lower = ~right_lower;
 
-      // Find the highest used bit.
-      int high = static_cast<int>(log2(left_upper));
-      high = Max(high, static_cast<int>(log2(left_lower)));
-      high = Max(high, static_cast<int>(log2(right_upper)));
-      high = Max(high, static_cast<int>(log2(right_lower)));
+      int high = MostSignificantBit(
+          left_upper | left_lower | right_upper | right_lower);
 
       int64_t limit = 1;
-      limit <<= high + 1;
+      limit <<= high;
       int32_t min = (left()->range()->CanBeNegative() ||
                      right()->range()->CanBeNegative())
                     ? static_cast<int32_t>(-limit) : 0;
       return new(zone) Range(min, static_cast<int32_t>(limit - 1));
     }
     return HValue::InferRange(zone);
   }
   const int32_t kDefaultMask = static_cast<int32_t>(0xffffffff);
   int32_t left_mask = (left()->range() != NULL)
       ? left()->range()->Mask()
@@ skipping 1443 matching lines @@
     case kBackingStore:
       if (!name_.is_null()) stream->Add(*String::cast(*name_)->ToCString());
       stream->Add("[backing-store]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal