[gcc r12-1115] tree-optimization/100778 - avoid cross-BB vectorization of trapping op

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:f7a07f5a5d8065e7f11133dd1f4ad3510ab2195b

commit r12-1115-gf7a07f5a5d8065e7f11133dd1f4ad3510ab2195b
Author: Richard Biener <rguenther@suse.de>
Date:   Fri May 28 14:26:06 2021 +0200

    tree-optimization/100778 - avoid cross-BB vectorization of trapping op
    
    This avoids vectorizing a possibly trapping operation when lanes
    are handled in different BBs.  I spotted this when working on the
    originally reported issue in PR100778.
    
    2021-05-28  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/100778
            * tree-vect-slp.c (vect_build_slp_tree_1): Prevent possibly
            trapping ops in different BBs.
    
            * gcc.dg/vect/bb-slp-pr100778-1.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/bb-slp-pr100778-1.c | 18 ++++++++++++++++++
 gcc/tree-vect-slp.c                           |  4 ++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr100778-1.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr100778-1.c
new file mode 100644
index 00000000000..9f8b7eecef1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr100778-1.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_double } */
+
+double foo (int x, double *p)
+{
+  double res = p[0] + p[1];
+  double tem = p[0] / x;
+  if (x)
+    {
+      p[0] = tem;
+      p[1] /= x;
+    }
+  return res + tem;
+}
+
+/* We may not SLP vectorize the FP division because it can trap and it
+   is distributed between two basic-blocks.  */
+/* { dg-final { scan-tree-dump "Build SLP failed: different BB for PHI or possibly trapping operation in _\[0-9\]+ = _\[0-9\]+ / _\[0-9\]+;" "slp2" } } */
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 0ec92b0f0ca..ca1539e63f2 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -1214,14 +1214,14 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char *swap,
 		}
 	    }
 
-	  if (phi_p
+	  if ((phi_p || gimple_could_trap_p (stmt_info->stmt))
 	      && (gimple_bb (first_stmt_info->stmt)
 		  != gimple_bb (stmt_info->stmt)))
 	    {
 	      if (dump_enabled_p ())
 		dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
 				 "Build SLP failed: different BB for PHI "
-				 "in %G", stmt);
+				 "or possibly trapping operation in %G", stmt);
 	      /* Mismatch.  */
 	      continue;
 	    }