[PATCH] sh, loop iv optim

[Christian BRUEL]

ahhhhh. yes this is true, loop-doloop.c should do the job. Thank you for 
the info, and your comments.

Kaz, it loos like we are missing a doloop_end pattern definition in the 
sh description. I'm giving it a try.

Best Regards,

Christian

Zdenek Dvorak wrote:
> Hello,
> 
> 
>>This patch provides an option, -f[no-]invert-ivs, that allows a loop 
>>exit to be tested against zero. This is very useful for architectures 
>>having a decrement and test instruction.
> 
> 
> we already have this optimization, see loop-doloop.c.  You should find
> out why it does not work for you on sh.  Nevertheless, some more comments:
> 
> 
>>Also, this optimisation exhibited a bug with the initialization of the 
>>number of iterations in loop-iv.c:iv_number_of_iterations that was 
>>handling the difference between pointers as a unsigned entity.
> 
> 
> That is correct, any differences computed in iv_number_of_iterations are
> unsigned.
> 
> 
>>as such 
>>the logical right shift was losing the sign bit. This case happened with 
>>a loop like
>>while (end > start) with an initial value of start > end.
> 
> 
> You need to check that noloop_assumptions is false before using
> the result of iv_number_of_iterations.  I.e.,
> 
> 
>>In this case 
>>the loop's number of iterations should be negative. To fix it I force 
>>the desc->signed_p to one when making a difference between two pointers 
>>and use a div instead of udiv. The code is less optimized but should be 
>>safe.
> 
> 
> this change is wrong.
> 
> 
>>	* loop-iv.c (iv_number_of_iterations): Make diffs between pointers 
>>	signed.
>>	(exit_on_zero_cond): New function.
>>	(need_guarded_loop): New function.
>>	(may_invert_loop): New function.
>>	(invert_loops): New function.
> 
> 
> New passes should be put to separate files.
> 
> 
>>+  for (i = 0; i < loop->num_nodes; i++)
>>+    {
>>+      basic_block bb;
>>+
>>+      bb = bbs[i];
>>+
>>+      /* Find the first conditional jump in the loop that depends on an iv.  */
> 
> 
> You would probably want to check here whether there is a loop exit edge
> from this bb, here.
> 
> 
>>+      cond = get_condition (BB_END (bb), &at, false, false);
>>+      if (cond)
>>+	{
>>+	  /* we want only the iv used as condition */
>>+	  for (i = 0; i < 2; i++)
>>+	    {
>>+	      rtx op = XEXP (cond, i);
>>+	      
>>+	      if (!CONSTANT_P (op) && iv_analyze_biv (op, &iv) 
>>+		  && iv.step != const0_rtx && !iv.first_special)
>>+		{
>>+		  edge_iterator ei;
>>+		  edge e;
>>+
>>+		  FOR_EACH_EDGE (e, ei, bb->succs)
>>+		    {
>>+		      basic_block bbe = e->dest;
>>+		      
>>+		      /* if this is an exit jump, take it when new iv
>>+			 reaches 0.  */
>>+		      if (LABEL_P (BB_HEAD (bbe))
>>+			  && BB_HEAD (bbe) == JUMP_LABEL (BB_END (bb)))
>>+			{
>>+			  *edgep = e;
>>+			  return cond;
>>+			}
> 
> 
> This is weird, I am not quite sure what are you trying to achieve.  If
> you are trying to find the edge taken when the condition is true, you
> should look for the edge without EDGE_FALLTHRU flag.
> 
> 
>>+/* Check if the number of iterations that will be decremented could be negative
>>+   and thus the first decrement and test would miss the first exit.  */
>>+
>>+static bool
>>+need_guarded_loop (struct loop *loop, rtx cond)
>>+{
>>+  struct niter_desc *desc;
>>+  enum rtx_code code = GET_CODE (cond);
>>+
>>+  desc = get_simple_loop_desc (loop);
>>+
>>+  if (CONSTANT_P (desc->niter_expr) || code == EQ || code == NE)
>>+    return false;
>>+
>>+  return true;
>>+}
> 
> 
> You want to check desc->noloop_assumptions here, instead.
> 
> Zdenek
>