[PATCH] Improve PR12245 compile-time by 50%

[Mark Mitchell]

Richard Guenther wrote:

> !   return (TREE_INT_CST_HIGH (t) ^ TREE_INT_CST_LOW (t)
> ! 	  ^ htab_hash_pointer (TREE_TYPE (t)));
>   }
>   
>   /* Return nonzero if the value represented by *X (an INTEGER_CST tree node)
> --- 712,719 ----
>   {
>     tree t = (tree) x;
>   
> !   return (TREE_INT_CST_HIGH (t) + TREE_INT_CST_LOW (t)
> ! 	  + (long)TREE_TYPE (t));

Shouldn't that cast be to HOST_WIDE_INT?  (It can't make for a better
hash function to throw away bits from the inputs....)

And, using + seems a bit unscientific, even if it happens to work well
in this case.

How about the hash_combine function from Boost:

http://www.boost.org/doc/html/hash_combine.html

?

-- 
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304