From: Richard Biener <rguenther@suse.de>
Date: Tue, 28 Jan 2025 14:01:25 +0000 (+0100)
Subject: tree-optimization/112859 - add comment
X-Git-Tag: releases/gcc-12.5.0~39
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e8b18dc45950f80d74e62ac7b4e3fa51d430d9cc;p=thirdparty%2Fgcc.git

tree-optimization/112859 - add comment

This adds a comment before the workaround, indicating flaky
dependence analysis.

	PR tree-optimization/112859
	* tree-loop-distribution.cc
	(loop_distribution::pg_add_dependence_edges): Add comment.

(cherry picked from commit 3ccbc8c9d182c380e396631b2b5a683de4fddba9)
---

diff --git a/gcc/tree-loop-distribution.cc b/gcc/tree-loop-distribution.cc
index 7b4fad238d5..8629b7fa75a 100644
--- a/gcc/tree-loop-distribution.cc
+++ b/gcc/tree-loop-distribution.cc
@@ -2137,7 +2137,9 @@ loop_distribution::pg_add_dependence_edges (struct graph *rdg, int dir,
 		      this_dir = -this_dir;
 		    }
 		  /* When then dependence distance of the innermost common
-		     loop of the DRs is zero we have a conflict.  */
+		     loop of the DRs is zero we have a conflict.  This is
+		     due to wonky dependence analysis which sometimes
+		     ends up using a zero distance in place of unknown.  */
 		  auto l1 = gimple_bb (DR_STMT (dr1))->loop_father;
 		  auto l2 = gimple_bb (DR_STMT (dr2))->loop_father;
 		  int idx = index_in_loop_nest (find_common_loop (l1, l2)->num,