From: Richard Biener <rguenther@suse.de>
Date: Tue, 19 Aug 2025 10:31:53 +0000 (+0200)
Subject: tree-optimization/121592 - failed reduction SLP discovery
X-Git-Tag: basepoints/gcc-17~5522
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=05284f73cff1685e2513b415e8da644193acf8cd;p=thirdparty%2Fgcc.git

tree-optimization/121592 - failed reduction SLP discovery

The testcase in the PR shows that when we have a reduction chain
with a wrapped conversion we fail to properly fall back to a
regular reduction, resulting in wrong-code.  The following fixes
this by failing discovery.  The testcase has other issues, so
I'm not including it here.

	PR tree-optimization/121592
	* tree-vect-slp.cc (vect_analyze_slp): When SLP reduction chain
	discovery fails, fail overall when the tail of the chain
	isn't also the entry for the non-SLP reduction.
---

diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 05363f89cf4..d5adb8baf87 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -5005,6 +5005,11 @@ vect_analyze_slp (vec_info *vinfo, unsigned max_tree_size,
 		vinfo = next;
 	      }
 	    STMT_VINFO_DEF_TYPE (first_element) = vect_internal_def;
+	    /* ???  When there's a conversion around the reduction
+	       chain 'last' isn't the entry of the reduction.  */
+	    if (STMT_VINFO_DEF_TYPE (last) != vect_reduction_def)
+	      return opt_result::failure_at (vect_location,
+					     "SLP build failed.\n");
 	    /* It can be still vectorized as part of an SLP reduction.  */
 	    loop_vinfo->reductions.safe_push (last);
 	  }