[PATCH] tree-optimization/95576 - fix compare-debug issue with SLP vectorization

[Richard Biener]

The following avoids leading debug stmts in BB vectorizer regions.

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

2020-06-10  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/95576
        * tree-vect-slp.c (vect_slp_bb): Skip leading debug stmts.

        * g++.dg/vect/pr95576.cc: New testcase.
---
 gcc/testsuite/g++.dg/vect/pr95576.cc | 23 +++++++++++++++++++++++
 gcc/tree-vect-slp.c                  |  7 ++++++-
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/vect/pr95576.cc

diff --git a/gcc/testsuite/g++.dg/vect/pr95576.cc 
b/gcc/testsuite/g++.dg/vect/pr95576.cc
new file mode 100644
index 00000000000..64e0e2dae7f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/vect/pr95576.cc
@@ -0,0 +1,23 @@
+// { dg-do compile }
+// { dg-additional-options "-O3 -fno-tree-forwprop -fcompare-debug" }
+
+struct S {
+  virtual ~S();
+  struct S *s;
+  virtual void m();
+  int f;
+  void *d;
+};
+
+struct T : S {
+  void m();
+};
+
+S::~S() {
+  if (s) {
+    s->f = 0;
+    s->d = __null;
+  }
+}
+
+void T::m() {}
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 0217a524f05..de82c198309 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -3316,7 +3316,12 @@ vect_slp_bb (basic_block bb)
        {
          gimple *stmt = gsi_stmt (gsi);
          if (is_gimple_debug (stmt))
-           continue;
+           {
+             /* Skip leading debug stmts.  */
+             if (gsi_stmt (region_begin) == stmt)
+               gsi_next (&region_begin);
+             continue;
+           }
          insns++;
 
          if (gimple_location (stmt) != UNKNOWN_LOCATION)
-- 
2.26.2