[patch] use __builtin_ctzl in ggc-page

[Steven Bosscher]

Hi,

The page allocator looks for free objects by keeping bitmaps of
taken slots in a bag.  We look for a 0 bit with a loop right now,
but we could use a builtin instead, like Nathan did recently for
the revamped bitmap.c.

Bootstrapped on x86_64-suse-linux-gnu, OK?

Gr.
Steven

	* ggc-page.c (ggc_alloc_stat): Use __builtin_ctzl instead of a
	loop to look for a free slot in a page entry.

Index: ggc-page.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/ggc-page.c,v
retrieving revision 1.96
diff -c -3 -p -r1.96 ggc-page.c
*** ggc-page.c	22 Oct 2004 17:05:05 -0000	1.96
--- ggc-page.c	14 Jan 2005 18:11:43 -0000
*************** ggc_alloc_stat (size_t size MEM_STAT_DEC
*** 1139,1146 ****
--- 1139,1152 ----
  	  word = bit = 0;
  	  while (~entry->in_use_p[word] == 0)
  	    ++word;
+ 
+ #if GCC_VERSION >= 3004
+ 	  bit = __builtin_ctzl (~entry->in_use_p[word]);
+ #else
  	  while ((entry->in_use_p[word] >> bit) & 1)
  	    ++bit;
+ #endif
+ 
  	  hint = word * HOST_BITS_PER_LONG + bit;
  	}