[PATCH] Fix noreturn predictor to also work with no regular exits

[PATCH] Fix noreturn predictor to also work with no regular exits

[Richard Guenther]

This is a complementary fix for the leslie3d problem.  For functions
without a regular exit (for example one that exits with exit (0))
we do not apply noreturn predictors.   The following patch notices
that edges to noreturn calls are still unlikely if they have
exactly one predecessor and is not fallthru.  In the leslie3d
case this avoids predicting the edges to STOP but still correctly
predicts the edges to the exceptional noreturn functions.

Bootstrap and regtest running on x86_64-unknown-linux-gnu, ok for trunk?

Thanks,
Richard.

2011-06-09  Richard Guenther  <rguenther@suse.de>

	* predict.c (tree_bb_level_predictions): For functions with
	no regular exit still predict the edge to a block with a noreturn
	function as not taken if it is not a fallthru edge.

Index: gcc/predict.c
===================================================================
--- gcc/predict.c	(revision 174746)
+++ gcc/predict.c	(working copy)
@@ -1613,10 +1613,18 @@ tree_bb_level_predictions (void)
 
 	  if (is_gimple_call (stmt))
 	    {
-	      if ((gimple_call_flags (stmt) & ECF_NORETURN)
-	          && has_return_edges)
-		predict_paths_leading_to (bb, PRED_NORETURN,
-					  NOT_TAKEN);
+	      if ((gimple_call_flags (stmt) & ECF_NORETURN))
+		{
+	          if (has_return_edges)
+		    predict_paths_leading_to (bb, PRED_NORETURN,
+					      NOT_TAKEN);
+		  else if (single_pred_p (bb))
+		    {
+		      edge e = single_pred_edge (bb);
+		      if (!(e->flags & EDGE_FALLTHRU))
+			predict_edge_def (e, PRED_NORETURN, NOT_TAKEN);
+		    }
+		}
 	      decl = gimple_call_fndecl (stmt);
 	      if (decl
 		  && lookup_attribute ("cold",

Re: [PATCH] Fix noreturn predictor to also work with no regular exits

[Richard Guenther]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 2043 bytes --]

On Thu, 9 Jun 2011, Richard Guenther wrote:

> 
> This is a complementary fix for the leslie3d problem.  For functions
> without a regular exit (for example one that exits with exit (0))
> we do not apply noreturn predictors.   The following patch notices
> that edges to noreturn calls are still unlikely if they have
> exactly one predecessor and is not fallthru.  In the leslie3d
> case this avoids predicting the edges to STOP but still correctly
> predicts the edges to the exceptional noreturn functions.
> 
> Bootstrap and regtest running on x86_64-unknown-linux-gnu, ok for trunk?

It regresses

FAIL: gcc.target/i386/umod-3.c scan-assembler-times divb 1

Richard.

> Thanks,
> Richard.
> 
> 2011-06-09  Richard Guenther  <rguenther@suse.de>
> 
> 	* predict.c (tree_bb_level_predictions): For functions with
> 	no regular exit still predict the edge to a block with a noreturn
> 	function as not taken if it is not a fallthru edge.
> 
> Index: gcc/predict.c
> ===================================================================
> --- gcc/predict.c	(revision 174746)
> +++ gcc/predict.c	(working copy)
> @@ -1613,10 +1613,18 @@ tree_bb_level_predictions (void)
>  
>  	  if (is_gimple_call (stmt))
>  	    {
> -	      if ((gimple_call_flags (stmt) & ECF_NORETURN)
> -	          && has_return_edges)
> -		predict_paths_leading_to (bb, PRED_NORETURN,
> -					  NOT_TAKEN);
> +	      if ((gimple_call_flags (stmt) & ECF_NORETURN))
> +		{
> +	          if (has_return_edges)
> +		    predict_paths_leading_to (bb, PRED_NORETURN,
> +					      NOT_TAKEN);
> +		  else if (single_pred_p (bb))
> +		    {
> +		      edge e = single_pred_edge (bb);
> +		      if (!(e->flags & EDGE_FALLTHRU))
> +			predict_edge_def (e, PRED_NORETURN, NOT_TAKEN);
> +		    }
> +		}
>  	      decl = gimple_call_fndecl (stmt);
>  	      if (decl
>  		  && lookup_attribute ("cold",
> 
> 

-- 
Richard Guenther <rguenther@suse.de>
Novell / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer