Re: fix up hot/cold partitioning on ports that don't have long conditional branches

[Mike Stump <mikestump@comcast.net>]

[-- Attachment #1: Type: text/plain, Size: 858 bytes --]

On Apr 22, 2011, at 3:28 AM, Eric Botcazou wrote:
>> This patch fixes up hot/cold partitioning on ports that don't have long
>> conditional branches.  I'll note that the entire file has lots of other
>> jump optimizations that are suspect.
> 
> Do you have a testcase for one of the ports in the tree?

Nope.  Found via an out of tree port with tree-prof.exp=pr34999.c.

> Note that parameters of function must be documented in the head comment.

Fixed.

> The patch contains long lines.

Didn't know we had switched over to caring that much.  Want me to fix all of gcc/*.[ch]?

> The ChangeLog entry doesn't look correct (relax_delay_slots mentioned 
> twice, no mention of the new parameter of follow_jumps, etc).

Fixed.

> How was the patch tested?

make check-gcc.

> Please generate patches with diff -p.

Done.


Ok?


[-- Attachment #2: reorg-cold-jumps.diffs.txt --]
[-- Type: text/plain, Size: 3807 bytes --]

2011-04-21  Mike Stump  <mikestump@comcast.net>

	* reorg.c (relax_delay_slots): Don't delete a jump that
	crosses a section boundary.  Pass insn to follow_jumps.
	(follow_jumps): Add jump parameter.  Don't replace a short
	conditional jump with a long conditional jump when the port
	doesn't have long conditional jumps.
	(fill_slots_from_thread): Pass insn to follow_jumps.

Index: reorg.c
===================================================================
--- reorg.c	(revision 1301)
+++ reorg.c	(working copy)
@@ -2501,15 +2501,18 @@ fill_simple_delay_slots (int non_jumps_p
 #endif
 }
 \f
-/* Follow any unconditional jump at LABEL;
-   return the ultimate label reached by any such chain of jumps.
-   Return null if the chain ultimately leads to a return instruction.
-   If LABEL is not followed by a jump, return LABEL.
-   If the chain loops or we can't find end, return LABEL,
-   since that tells caller to avoid changing the insn.  */
+/* Follow any unconditional jump at LABEL; return the ultimate label
+   reached by any such chain of jumps.  Return null if the chain
+   ultimately leads to a return instruction.  If LABEL is not followed
+   by a jump, return LABEL.  If the chain loops or we can't find end,
+   return LABEL, since that tells caller to avoid changing the insn.
+   If the chain of jumps ever crosses a section boundary, and the port
+   doesn't have long condition branches and the JUMP that we are
+   performing this analysis for was a conditional branch, return the
+   first such label before any such crossing.  */
 
 static rtx
-follow_jumps (rtx label)
+follow_jumps (rtx label, rtx jump)
 {
   rtx insn;
   rtx next;
@@ -2529,6 +2532,16 @@ follow_jumps (rtx label)
     {
       rtx tem;
 
+      /* If a label crosses a section boundary and we're thinking
+	 about changing a conditional jump to be a conditional jump
+	 across that boundary, don't do it if the port doesn't have
+	 long conditional branches.  We can however jump to the label
+	 just before we cross such a boundary.  */
+      if (!HAS_LONG_COND_BRANCH
+	  && find_reg_note (insn, REG_CROSSING_JUMP, NULL_RTX)
+	  && any_condjump_p (jump))
+	return value;
+
       /* If we have found a cycle, make the insn jump to itself.  */
       if (JUMP_LABEL (insn) == label)
 	return label;
@@ -2991,7 +3004,7 @@ fill_slots_from_thread (rtx insn, rtx co
 	  && redirect_with_delay_list_safe_p (insn,
 					      JUMP_LABEL (new_thread),
 					      delay_list))
-	new_thread = follow_jumps (JUMP_LABEL (new_thread));
+	new_thread = follow_jumps (JUMP_LABEL (new_thread), new_thread);
 
       if (new_thread == 0)
 	label = find_end_label ();
@@ -3342,12 +3355,14 @@ relax_delay_slots (rtx first)
 	  && (condjump_p (insn) || condjump_in_parallel_p (insn))
 	  && (target_label = JUMP_LABEL (insn)) != 0)
 	{
-	  target_label = skip_consecutive_labels (follow_jumps (target_label));
+	  target_label = skip_consecutive_labels (follow_jumps (target_label,
+								insn));
 	  if (target_label == 0)
 	    target_label = find_end_label ();
 
 	  if (target_label && next_active_insn (target_label) == next
-	      && ! condjump_in_parallel_p (insn))
+	      && ! condjump_in_parallel_p (insn)
+	      && find_reg_note (insn, REG_CROSSING_JUMP, NULL_RTX) == NULL_RTX)
 	    {
 	      delete_jump (insn);
 	      continue;
@@ -3492,7 +3507,8 @@ relax_delay_slots (rtx first)
 	{
 	  /* If this jump goes to another unconditional jump, thread it, but
 	     don't convert a jump into a RETURN here.  */
-	  trial = skip_consecutive_labels (follow_jumps (target_label));
+	  trial = skip_consecutive_labels (follow_jumps (target_label,
+							 delay_insn));
 	  if (trial == 0)
 	    trial = find_end_label ();