This fixes the case where the insertion iterator for the live stmt
is the end of a BB by adjusting the dominance query to the definition
of the def we're substituting.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

2020-10-15  Richard Biener  <rguent...@suse.de>

        * tree-vect-loop.c (vectorizable_live_operation): Adjust
        dominance query.

        * gcc.dg/vect/bb-slp-52.c: New testcase.
---
 gcc/testsuite/gcc.dg/vect/bb-slp-52.c | 15 +++++++++++++++
 gcc/tree-vect-loop.c                  |  7 +++++--
 2 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-52.c

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-52.c 
b/gcc/testsuite/gcc.dg/vect/bb-slp-52.c
new file mode 100644
index 00000000000..5194af8cc40
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-52.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+int a, e;
+void g(float);
+typedef struct {
+  float b, c;
+} d;
+d f;
+void h(double i, double j) {
+  if (a && e)
+    return;
+  f.b = j;
+  f.c = i;
+  g(i);
+}
diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index 0a315e22226..991fd457229 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -8395,8 +8395,11 @@ vectorizable_live_operation (vec_info *vinfo,
               were not code-generated yet so it is not too bad.
               ???  In fact we'd likely want to avoid this situation
               in the first place.  */
-           if (gimple_code (use_stmt) != GIMPLE_PHI
-               && !vect_stmt_dominates_stmt_p (gsi_stmt (*gsi), use_stmt))
+           if (TREE_CODE (new_tree) == SSA_NAME
+               && !SSA_NAME_IS_DEFAULT_DEF (new_tree)
+               && gimple_code (use_stmt) != GIMPLE_PHI
+               && !vect_stmt_dominates_stmt_p (SSA_NAME_DEF_STMT (new_tree),
+                                               use_stmt))
              {
                enum tree_code code = gimple_assign_rhs_code (use_stmt);
                gcc_assert (code == CONSTRUCTOR
-- 
2.26.2

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