Re: [PATCH] tree-optimization/101280 - revise interchange fix for PR101173

[Richard Biener <rguenther@suse.de>]

On Fri, 2 Jul 2021, Richard Biener wrote:

> On Thu, 1 Jul 2021, Michael Matz wrote:
> 
> > Hello,
> > 
> > On Thu, 1 Jul 2021, Richard Biener wrote:
> > 
> > > diff --git a/gcc/gimple-loop-interchange.cc b/gcc/gimple-loop-interchange.cc
> > > index 43045c5455e..43ef112a2d0 100644
> > > --- a/gcc/gimple-loop-interchange.cc
> > > +++ b/gcc/gimple-loop-interchange.cc
> > > @@ -1043,8 +1043,11 @@ tree_loop_interchange::valid_data_dependences (unsigned i_idx, unsigned o_idx,
> > >  	    continue;
> > >  
> > >  	  /* Be conservative, skip case if either direction at i_idx/o_idx
> > > -	     levels is not '=' (for the inner loop) or '<'.  */
> > > -	  if (dist_vect[i_idx] < 0 || dist_vect[o_idx] <= 0)
> > > +	     levels is not '=' or '<'.  */
> > > +	  if (dist_vect[i_idx] < 0
> > > +	      || (DDR_REVERSED_P (ddr) && dist_vect[i_idx] > 0)
> > > +	      || dist_vect[o_idx] < 0
> > > +	      || (DDR_REVERSED_P (ddr) && dist_vect[o_idx] > 0))
> > 
> > Hmm, if DDR_REVERSED_P matters here, then it should matter for all arms.  
> > IOW: < 0 should be tested only when !DDR_REVERSED_P, not always:
> > 
> >        if ((!DDR_REVERSED_P (ddr) && dist_vect[i_idx] < 0)
> >            || (DDR_REVERSED_P (ddr) && dist_vect[i_idx] > 0)
> >            || (!DDR_REVERSED_P (ddr) && dist_vect[o_idx] < 0)
> >            || (DDR_REVERSED_P (ddr) && dist_vect[o_idx] > 0))
> > 
> > (what you have effectively written is a condition that allows only 0 when 
> > DDR_REVERSED_P)
> 
> True - been fixing bugs too fast I guess.  Maybe the 3rd time's the charm 
> then ;)

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

Richard.

From 094af28137de5c55a21123c3b4e06e7d7a08bb5a Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Fri, 2 Jul 2021 08:51:43 +0200
Subject: [PATCH] tree-optimization/101280 - re-revise interchange fix for
 PR101173
To: gcc-patches@gcc.gnu.org

The following fixes up the revision of the original fix for PR101173
to properly guard all dependence checks with DDR_REVERSED_P or its
inverse.

2021-07-01  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101280
	PR tree-optimization/101173
	* gimple-loop-interchange.cc
	(tree_loop_interchange::valid_data_dependences): Properly
	guard all dependence checks with DDR_REVERSED_P or its
	inverse.
---
 gcc/gimple-loop-interchange.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/gimple-loop-interchange.cc b/gcc/gimple-loop-interchange.cc
index 43ef112a2d0..7a88faa2c07 100644
--- a/gcc/gimple-loop-interchange.cc
+++ b/gcc/gimple-loop-interchange.cc
@@ -1044,9 +1044,9 @@ tree_loop_interchange::valid_data_dependences (unsigned i_idx, unsigned o_idx,
 
 	  /* Be conservative, skip case if either direction at i_idx/o_idx
 	     levels is not '=' or '<'.  */
-	  if (dist_vect[i_idx] < 0
+	  if ((!DDR_REVERSED_P (ddr) && dist_vect[i_idx] < 0)
 	      || (DDR_REVERSED_P (ddr) && dist_vect[i_idx] > 0)
-	      || dist_vect[o_idx] < 0
+	      || (!DDR_REVERSED_P (ddr) && dist_vect[o_idx] < 0)
 	      || (DDR_REVERSED_P (ddr) && dist_vect[o_idx] > 0))
 	    return false;
 	}
-- 
2.26.2