[gcc r11-3527] tree-optimization/97241 - fix ICE in reduction vectorization

[Richard Biener]

https://gcc.gnu.org/g:39a27bb01aa223ce89946f0a4de6b60c4c0b03d2

commit r11-3527-g39a27bb01aa223ce89946f0a4de6b60c4c0b03d2
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Sep 29 15:02:47 2020 +0200

    tree-optimization/97241 - fix ICE in reduction vectorization
    
    The following moves an ad-hoc attempt at discovering the SLP node
    for a stmt to the place where we can find it in lock-step when
    we find the stmt itself.
    
    2020-09-29  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/97241
            * tree-vect-loop.c (vectorizable_reduction): Move finding
            the SLP node for the reduction stmt to a better place.
    
            * gcc.dg/vect/pr97241.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr97241.c | 19 +++++++++++++++++++
 gcc/tree-vect-loop.c                | 17 +++++------------
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/pr97241.c b/gcc/testsuite/gcc.dg/vect/pr97241.c
new file mode 100644
index 00000000000..d4be8f60940
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr97241.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 --param max-loop-header-insns=2" } */
+
+short int *ev;
+int l4;
+
+short int
+a7 (void)
+{
+  short int uo = ev[0], ie = uo;
+
+  for (int kp = 0; kp < l4; kp += 4)
+    {
+      uo += ev[kp + 1];
+      ie += ev[kp];
+    }
+
+  return uo + ie;
+}
diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index f1d6bdde412..ce5d95d7277 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -6357,12 +6357,14 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
   gphi *reduc_def_phi = as_a <gphi *> (phi_info->stmt);
 
   /* Verify following REDUC_IDX from the latch def leads us back to the PHI
-     and compute the reduction chain length.  */
+     and compute the reduction chain length.  Discover the real
+     reduction operation stmt on the way (stmt_info and slp_for_stmt_info).  */
   tree reduc_def = PHI_ARG_DEF_FROM_EDGE (reduc_def_phi,
 					  loop_latch_edge (loop));
   unsigned reduc_chain_length = 0;
   bool only_slp_reduc_chain = true;
   stmt_info = NULL;
+  slp_tree slp_for_stmt_info = slp_node ? slp_node_instance->root : NULL;
   while (reduc_def != PHI_RESULT (reduc_def_phi))
     {
       stmt_vec_info def = loop_vinfo->lookup_def (reduc_def);
@@ -6405,6 +6407,8 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
 	stmt_info = vdef;
       reduc_def = gimple_op (vdef->stmt, 1 + STMT_VINFO_REDUC_IDX (vdef));
       reduc_chain_length++;
+      if (!stmt_info && slp_node)
+	slp_for_stmt_info = SLP_TREE_CHILDREN (slp_for_stmt_info)[0];
     }
   /* PHIs should not participate in patterns.  */
   gcc_assert (!STMT_VINFO_RELATED_STMT (phi_info));
@@ -6491,17 +6495,6 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
      The last use is the reduction variable.  In case of nested cycle this
      assumption is not true: we use reduc_index to record the index of the
      reduction variable.  */
-  /* ???  To get at invariant/constant uses on the SLP node we have to
-     get to it here, slp_node is still the reduction PHI.  */
-  slp_tree slp_for_stmt_info = NULL;
-  if (slp_node)
-    {
-      slp_for_stmt_info = slp_node_instance->root;
-      /* And then there's reduction chain with a conversion ...  */
-      if (SLP_TREE_REPRESENTATIVE (slp_for_stmt_info) != stmt_info)
-	slp_for_stmt_info = SLP_TREE_CHILDREN (slp_for_stmt_info)[0];
-      gcc_assert (SLP_TREE_REPRESENTATIVE (slp_for_stmt_info) == stmt_info);
-    }
   slp_tree *slp_op = XALLOCAVEC (slp_tree, op_type);
   /* We need to skip an extra operand for COND_EXPRs with embedded
      comparison.  */