[gcc r17-3282] tree-optimization/126852 - verify SLP schedule also for PHIs

https://gcc.gnu.org/g:6a000bf53e6f42cff3774822227f47e39d2b76d5

commit r17-3282-g6a000bf53e6f42cff3774822227f47e39d2b76d5
Author: Richard Biener <[email protected]>
Date:   Fri Aug 14 10:57:17 2026 +0200

    tree-optimization/126852 - verify SLP schedule also for PHIs
    
    We have to verify the PHI argument nodes insertion place dominates
    the PHI argument edge sources.
    
            PR tree-optimization/126852
            * tree-vect-slp.cc (vect_schedule_slp_node): Verify schedule
            for PHIs.
    
            * gcc.dg/vect/bb-slp-pr126852.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/bb-slp-pr126852.c | 25 +++++++++++++++++++++++++
 gcc/tree-vect-slp.cc                        | 10 ++++++++++
 2 files changed, 35 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr126852.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr126852.c
new file mode 100644
index 000000000000..5391a08d3144
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr126852.c
@@ -0,0 +1,25 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O3 -fno-tree-pre" } */
+/* { dg-additional-options "-mavx2" { target avx2 } } */
+
+int a;
+long b, c;
+__attribute__((noinline)) int d() {
+  a = 0;
+  return 0;
+}
+void e(char f, char g, long h, long i) {
+  char j;
+k:
+  do {
+    j = 2 * f;
+    if (!g)
+      return;
+    d();
+    if (g << g)
+      goto k;
+    unsigned long m = b;
+    long n = m >> 8;
+    c = n + 2088470516281635866 * i + h * h + 7017580219 * i;
+  } while (j < f + 2);
+}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index d1bf3499eb7e..bda7ae679e55 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -12117,6 +12117,16 @@ vect_schedule_slp_node (vec_info *vinfo,
     {
       /* For PHI node vectorization we do not use the insertion iterator.  */
       last_stmt = SLP_TREE_SCALAR_STMTS (node)[0]->stmt;
+      if (place_only)
+	FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
+	  {
+	    if (child->si
+		&& !dominated_by_p (CDI_DOMINATORS,
+				    gimple_phi_arg_edge
+				      (as_a <gphi *> (last_stmt), i)->src,
+				    gimple_bb (child->si)))
+	      return false;
+	  }
       si = gsi_none ();
     }
   else