Do not apply loop alignment to final block

[Eric Botcazou]

The alignment code in final.c uses some heuristics to decide what alignment a 
block must be given.  For the loop alignment, it's:

       /* In case block is frequent and reached mostly by non-fallthru edge,
         align it.  It is most likely a first block of loop.  */

An immediate counter-example is a final block (block falling through to the 
exit) reached mostly by early returns.  There are 8 examples at -O2 in the 
gcc.c-torture/compile testsuite on x86-64.

Tested on x86_64-suse-linux, applied on the mainline.


2014-04-16  Eric Botcazou  <ebotca...@adacore.com>

        * final.c (compute_alignments): Do not apply loop alignment to a block
        falling through to the exit.


-- 
Eric Botcazou
Index: final.c
===================================================================
--- final.c	(revision 209443)
+++ final.c	(working copy)
@@ -775,6 +775,8 @@ compute_alignments (void)
       /* In case block is frequent and reached mostly by non-fallthru edge,
 	 align it.  It is most likely a first block of loop.  */
       if (has_fallthru
+	  && !(single_succ_p (bb)
+	       && single_succ (bb) == EXIT_BLOCK_PTR_FOR_FN (cfun))
 	  && optimize_bb_for_speed_p (bb)
 	  && branch_frequency + fallthru_frequency > freq_threshold
 	  && (branch_frequency