[PATCH] SLP vectorize across PHI nodes

Christophe Lyon christophe.lyon@linaro.org
Wed Oct 28 10:27:37 GMT 2020


On Tue, 27 Oct 2020 at 13:18, Richard Biener <rguenther@suse.de> wrote:
>
> This makes SLP discovery detect backedges by seeding the bst_map with
> the node to be analyzed so it can be picked up from recursive calls.
> This removes the need to discover backedges in a separate walk.
>
> This enables SLP build to handle PHI nodes in full, continuing
> the SLP build to non-backedges.  For loop vectorization this
> enables outer loop vectorization of nested SLP cycles and for
> BB vectorization this enables vectorization of PHIs at CFG merges.
>
> It also turns code generation into a SCC discovery walk to handle
> irreducible regions and nodes only reachable via backedges where
> we now also fill in vectorized backedge defs.
>
> This requires sanitizing the SLP tree for SLP reduction chains even
> more, manually filling the backedge SLP def.
>
> This also exposes the fact that CFG copying (and edge splitting
> until I fixed that) ends up with different edge order in the
> copy which doesn't play well with the desired 1:1 mapping of
> SLP PHI node children and edges for epilogue vectorization.
> I've tried to fixup CFG copying here but this really looks
> like a dead (or expensive) end there so I've done fixup in
> slpeel_tree_duplicate_loop_to_edge_cfg instead for the cases
> we can run into.
>
> There's still NULLs in the SLP_TREE_CHILDREN vectors and I'm
> not sure it's possible to eliminate them all this stage1 so the
> patch has quite some checks for this case all over the place.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.  SPEC CPU 2017
> and SPEC CPU 2006 successfully built and tested.
>
> Will push soon.
>
> Richard.
>
> 2020-10-27  Richard Biener  <rguenther@suse.de>
>
>         * gimple.h (gimple_expr_type): For PHIs return the type
>         of the result.
>         * tree-vect-loop-manip.c (slpeel_tree_duplicate_loop_to_edge_cfg):
>         Make sure edge order into copied loop headers line up with the
>         originals.
>         * tree-vect-loop.c (vect_transform_cycle_phi): Handle nested
>         loops with SLP.
>         (vectorizable_phi): New function.
>         (vectorizable_live_operation): For BB vectorization compute insert
>         location here.
>         * tree-vect-slp.c (vect_free_slp_tree): Deal with NULL
>         SLP_TREE_CHILDREN entries.
>         (vect_create_new_slp_node): Add overloads with pre-existing node
>         argument.
>         (vect_print_slp_graph): Likewise.
>         (vect_mark_slp_stmts): Likewise.
>         (vect_mark_slp_stmts_relevant): Likewise.
>         (vect_gather_slp_loads): Likewise.
>         (vect_optimize_slp): Likewise.
>         (vect_slp_analyze_node_operations): Likewise.
>         (vect_bb_slp_scalar_cost): Likewise.
>         (vect_remove_slp_scalar_calls): Likewise.
>         (vect_get_and_check_slp_defs): Handle PHIs.
>         (vect_build_slp_tree_1): Handle PHIs.
>         (vect_build_slp_tree_2): Continue SLP build, following PHI
>         arguments.  Fix memory leak.
>         (vect_build_slp_tree): Put stub node into the hash-map so
>         we can discover cycles directly.
>         (vect_build_slp_instance): Set the backedge SLP def for
>         reduction chains.
>         (vect_analyze_slp_backedges): Remove.
>         (vect_analyze_slp): Do not call it.
>         (vect_slp_convert_to_external): Release SLP_TREE_LOAD_PERMUTATION.
>         (vect_slp_analyze_node_operations): Handle stray failed
>         backedge defs by failing.
>         (vect_slp_build_vertices): Adjust leaf condition.
>         (vect_bb_slp_mark_live_stmts): Handle PHIs, use visited
>         hash-set to handle cycles.
>         (vect_slp_analyze_operations): Adjust.
>         (vect_bb_partition_graph_r): Likewise.
>         (vect_slp_function): Adjust split condition to allow CFG
>         merges.
>         (vect_schedule_slp_instance): Rename to ...
>         (vect_schedule_slp_node): ... this.  Move DFS walk to ...
>         (vect_schedule_scc): ... this new function.
>         (vect_schedule_slp): Call it.  Remove ad-hoc vectorized
>         backedge fill code.
>         * tree-vect-stmts.c (vect_analyze_stmt): Call
>         vectorizable_phi.
>         (vect_transform_stmt): Likewise.
>         (vect_is_simple_use): Handle vect_backedge_def.
>         * tree-vectorizer.c (vec_info::new_stmt_vec_info): Only
>         set loop header PHIs to vect_unknown_def_type for loop
>         vectorization.
>         * tree-vectorizer.h (enum vect_def_type): Add vect_backedge_def.
>         (enum stmt_vec_info_type): Add phi_info_type.
>         (vectorizable_phi): Declare.
>
>         * gcc.dg/vect/bb-slp-54.c: New test.
>         * gcc.dg/vect/bb-slp-55.c: Likewise.
>         * gcc.dg/vect/bb-slp-56.c: Likewise.
>         * gcc.dg/vect/bb-slp-57.c: Likewise.
>         * gcc.dg/vect/bb-slp-58.c: Likewise.
>         * gcc.dg/vect/bb-slp-59.c: Likewise.
>         * gcc.dg/vect/bb-slp-60.c: Likewise.
>         * gcc.dg/vect/bb-slp-61.c: Likewise.
>         * gcc.dg/vect/bb-slp-62.c: Likewise.
>         * gcc.dg/vect/bb-slp-63.c: Likewise.
>         * gcc.dg/vect/bb-slp-64.c: Likewise.
>         * gcc.dg/vect/bb-slp-65.c: Likewise.
>         * gcc.dg/vect/bb-slp-66.c: Likewise.
>         * gcc.dg/vect/vect-outer-slp-1.c: Likewise.
>         * gfortran.dg/vect/O3-bb-slp-1.f: Likewise.
>         * gfortran.dg/vect/O3-bb-slp-2.f: Likewise.
>         * g++.dg/vect/simd-11.cc: Likewise.


I've filed https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97616
because bb-slp-58.c and bb-slp-59.c fail on arm.

> ---
>  gcc/gimple.h                                 |   2 +
>  gcc/testsuite/g++.dg/vect/simd-11.cc         |  61 ++
>  gcc/testsuite/gcc.dg/vect/bb-slp-54.c        |  23 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-55.c        |  18 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-56.c        |  17 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-57.c        |  38 ++
>  gcc/testsuite/gcc.dg/vect/bb-slp-58.c        |  23 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-59.c        |  25 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-60.c        |  18 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-61.c        |  26 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-62.c        |  21 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-63.c        |  21 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-64.c        |  11 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-65.c        |  15 +
>  gcc/testsuite/gcc.dg/vect/bb-slp-66.c        |  32 +
>  gcc/testsuite/gcc.dg/vect/vect-outer-slp-1.c |  31 +
>  gcc/testsuite/gfortran.dg/vect/O3-bb-slp-1.f |  28 +
>  gcc/testsuite/gfortran.dg/vect/O3-bb-slp-2.f |  40 ++
>  gcc/tree-vect-loop-manip.c                   |  27 +
>  gcc/tree-vect-loop.c                         | 112 +++-
>  gcc/tree-vect-slp.c                          | 664 ++++++++++++-------
>  gcc/tree-vect-stmts.c                        |   8 +-
>  gcc/tree-vectorizer.c                        |   3 +-
>  gcc/tree-vectorizer.h                        |   2 +
>  24 files changed, 1031 insertions(+), 235 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/vect/simd-11.cc
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-54.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-55.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-56.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-57.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-58.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-59.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-60.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-61.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-62.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-63.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-64.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-65.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-66.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-outer-slp-1.c
>  create mode 100644 gcc/testsuite/gfortran.dg/vect/O3-bb-slp-1.f
>  create mode 100644 gcc/testsuite/gfortran.dg/vect/O3-bb-slp-2.f
>
> diff --git a/gcc/gimple.h b/gcc/gimple.h
> index 3c9b9965f5a..87c90be9a6a 100644
> --- a/gcc/gimple.h
> +++ b/gcc/gimple.h
> @@ -6598,6 +6598,8 @@ gimple_expr_type (const gimple *stmt)
>      }
>    else if (code == GIMPLE_COND)
>      return boolean_type_node;
> +  else if (code == GIMPLE_PHI)
> +    return TREE_TYPE (gimple_phi_result (stmt));
>    else
>      return void_type_node;
>  }
> diff --git a/gcc/testsuite/g++.dg/vect/simd-11.cc b/gcc/testsuite/g++.dg/vect/simd-11.cc
> new file mode 100644
> index 00000000000..912d1840055
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/vect/simd-11.cc
> @@ -0,0 +1,61 @@
> +// { dg-do compile }
> +// { dg-require-effective-target c++11 }
> +// { dg-additional-options "-Ofast" }
> +
> +template <typename> class h {
> +public:
> +  ~h();
> +};
> +template <typename> struct l;
> +template <typename c> struct l<h<c> > {
> +  using d = c;
> +  template <typename e> using f = h<e>;
> +};
> +template <typename g> struct o {
> +  typedef l<g> j;
> +  typedef typename j::d k;
> +  template <typename c> struct p { typedef typename j::f<c> m; };
> +};
> +template <typename c, typename g> struct F {
> +  typedef typename o<g>::p<c>::m q;
> +  struct : q {
> +  } r;
> +};
> +template <typename c, typename g = h<c> > class s : F<c, g> {
> +public:
> +  s(long);
> +  typename o<typename F<c, g>::q>::k operator[](long);
> +};
> +template <int> class t {
> +public:
> +  int dimension;
> +  t(const t &);
> +  void operator+=(t);
> +  double values[];
> +};
> +template <int dim> t<dim>::t(const t &p1) {
> +  for (int i = 0; i < dim; ++i)
> +    values[i] = p1.values[i];
> +}
> +template <int dim> class u : public t<dim> {
> +public:
> +  double m_fn1(const u &) const;
> +};
> +template <int dim> double u<dim>::m_fn1(const u &) const {
> +  double a;
> +  for (int i = 0; i < dim; ++i) {
> +    double b = this->values[i];
> +    a += b;
> +  }
> +  return a;
> +}
> +int m_fn2(const u<2> &p1, const u<2> &w) {
> +  int n;
> +  s<u<2> > c(n);
> +  s<double> d(n);
> +  double e = p1.m_fn1(w);
> +  for (;;) {
> +    c[0] += p1;
> +    d = e;
> +  }
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-54.c b/gcc/testsuite/gcc.dg/vect/bb-slp-54.c
> new file mode 100644
> index 00000000000..d05ce33310d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-54.c
> @@ -0,0 +1,23 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target vect_double } */
> +
> +double a[2], b[2], c[2];
> +
> +void foo(int flag)
> +{
> +  double tem1, tem2;
> +  if (flag)
> +    {
> +      tem1 = a[0];
> +      tem2 = a[1];
> +    }
> +  else
> +    {
> +      tem1 = b[0];
> +      tem2 = b[1];
> +    }
> +  c[0] = tem1;
> +  c[1] = tem2;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "transform load" 2 "slp2" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-55.c b/gcc/testsuite/gcc.dg/vect/bb-slp-55.c
> new file mode 100644
> index 00000000000..57a042b0ba5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-55.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +
> +typedef struct {
> +  int a;
> +  int b;
> +  int c;
> +  int d;
> +} e;
> +e *f;
> +int g;
> +void h() {
> +  e *i;
> +  if (g) {
> +    i->c = f[g].b;
> +    i->d = f[g].a;
> +  } else
> +    i->c = i->d = 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-56.c b/gcc/testsuite/gcc.dg/vect/bb-slp-56.c
> new file mode 100644
> index 00000000000..90d17512492
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-56.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +
> +typedef struct {
> +  double a, b;
> +} c;
> +int d, e;
> +int i(void);
> +void h(c, c);
> +void f() {
> +  c a, g;
> +  do {
> +    a.a = e ?: g.a;
> +    a.b = g.b + d;
> +    h(g, a);
> +    g = a;
> +  } while (i());
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-57.c b/gcc/testsuite/gcc.dg/vect/bb-slp-57.c
> new file mode 100644
> index 00000000000..6f13507fd67
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-57.c
> @@ -0,0 +1,38 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-ffast-math" } */
> +/* { dg-require-effective-target vect_float } */
> +
> +float *a;
> +typedef struct {
> +  int c;
> +  float bbmax[3];
> +} d;
> +d e;
> +int f[3];
> +int g, h, i, j;
> +float k, k;
> +void l()
> +{
> +  for (unsigned z = 0; z < 2048; ++z) {
> +    {
> +      j = e.bbmax[1] > k ? e.bbmax[1] : k;
> +    }
> +    e.bbmax[1] = j;
> +    { i = e.bbmax[2] > k ? e.bbmax[2] : k; }
> +    e.bbmax[2] = i;
> +    f[2] = a[2];
> +    {
> +      float b;
> +      h = e.bbmax[1] > b ? e.bbmax[1] : b;
> +    }
> +    e.bbmax[1] = h;
> +    {
> +      float b;
> +      g = e.bbmax[2] > b ? e.bbmax[2] : b;
> +    }
> +    e.bbmax[2] = g;
> +  }
> +}
> +
> +/* { dg-final { scan-tree-dump-times "transform load" 1 "slp1" { target { { x86_64-*-* i?86-*-* } && lp64 } } } } */
> +/* { dg-final { scan-tree-dump "optimized: basic block" "slp1" { target { { x86_64-*-* i?86-*-* } && lp64 } } } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-58.c b/gcc/testsuite/gcc.dg/vect/bb-slp-58.c
> new file mode 100644
> index 00000000000..11bf5c333ab
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-58.c
> @@ -0,0 +1,23 @@
> +/* { dg-do compile } */
> +
> +double x[1024];
> +void bar (void);
> +
> +void foo (void)
> +{
> +  double tem1 = x[0];
> +  double tem2 = x[1];
> +  for (int i = 0; i < 511; ++i)
> +    {
> +      x[2*i] = tem1;
> +      x[2*i+1] = tem2;
> +      bar ();
> +      tem1 = x[2*(i+1)];
> +      tem2 = x[2*(i+1)+1];
> +    }
> +}
> +
> +/* We should be able to vectorize the cycle in one SLP attempt including
> +   both load groups.  */
> +/* { dg-final { scan-tree-dump-times "transform load" 2 "slp1" } } */
> +/* { dg-final { scan-tree-dump-times "optimized: basic block" 1 "slp1" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-59.c b/gcc/testsuite/gcc.dg/vect/bb-slp-59.c
> new file mode 100644
> index 00000000000..2e35725ff2a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-59.c
> @@ -0,0 +1,25 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-fdump-tree-loopdone" } */
> +
> +double x[1024];
> +void bar (void);
> +
> +void foo (void)
> +{
> +  double tem1 = x[0];
> +  double tem2 = x[1];
> +  for (int i = 0; i < 511; ++i)
> +    {
> +      x[2*i] = tem2;
> +      x[2*i+1] = tem1;
> +      bar ();
> +      tem1 = x[2*(i+1)];
> +      tem2 = x[2*(i+1)+1];
> +    }
> +}
> +
> +/* We should be able to vectorize the cycle in one SLP attempt including
> +   both load groups and do only one permutation.  */
> +/* { dg-final { scan-tree-dump-times "transform load" 2 "slp1" } } */
> +/* { dg-final { scan-tree-dump-times "VEC_PERM_EXPR" 1 "loopdone" } } */
> +/* { dg-final { scan-tree-dump-times "optimized: basic block" 1 "slp1" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-60.c b/gcc/testsuite/gcc.dg/vect/bb-slp-60.c
> new file mode 100644
> index 00000000000..52643bfd75a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-60.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +
> +enum { a = 1, b };
> +float *c, *e;
> +float d, h;
> +int f, g;
> +void i()
> +{
> +  float j = h;
> +  for (; g;)
> +    for (; f; f++)
> +      {
> +       c[a] = j * d;
> +       c[b] = h * d;
> +       j = 0;
> +       h = e[2];
> +      }
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-61.c b/gcc/testsuite/gcc.dg/vect/bb-slp-61.c
> new file mode 100644
> index 00000000000..3323a2bb2d9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-61.c
> @@ -0,0 +1,26 @@
> +/* { dg-do compile } */
> +
> +struct a {
> +  enum { b, c } d;
> +  unsigned e;
> +  unsigned f;
> +};
> +void j(struct a *a, int i, int h)
> +{
> +  unsigned f = a->f;
> +  switch (a->d)
> +    while (1)
> +      {
> +        if (i)
> +          {
> +    case b:
> +            if (h)
> +              goto k;
> +          }
> +        else
> +          f = 0;
> +    case c:;
> +      }
> +k:
> +  a->e = a->f = f;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-62.c b/gcc/testsuite/gcc.dg/vect/bb-slp-62.c
> new file mode 100644
> index 00000000000..84ee04c1013
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-62.c
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +
> +typedef struct {
> +  char a;
> +  int b[];
> +} c;
> +int d, f;
> +c e;
> +void g() {
> +  int h, i, j;
> +  for (; i;)
> +    switch (i)
> +    case 4: {
> +      h = (__UINTPTR_TYPE__)g >= 3;
> +      for (; h; h -= 1)
> +        if (d)
> +          j = f;
> +    }
> +      for (; i < 3; i++)
> +        e.b[i] = j;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-63.c b/gcc/testsuite/gcc.dg/vect/bb-slp-63.c
> new file mode 100644
> index 00000000000..6519c9752fe
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-63.c
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +
> +struct {
> +  unsigned a;
> +  unsigned c;
> +} d;
> +int e, g;
> +void h(unsigned b) {
> +  unsigned a, c;
> +  while (e) {
> +    if (b) {
> +      ++e;
> +      continue;
> +    }
> +    c = g;
> +    if (g)
> +      a |= 10;
> +  }
> +  d.a = a;
> +  d.c = c;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-64.c b/gcc/testsuite/gcc.dg/vect/bb-slp-64.c
> new file mode 100644
> index 00000000000..dcb6a1455c3
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-64.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +
> +enum { a, b };
> +double *c, *e;
> +int d, f;
> +void g() {
> +  for (;;) {
> +    c[a] = c[b] = d * e[b];
> +    f = d -= f;
> +  }
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-65.c b/gcc/testsuite/gcc.dg/vect/bb-slp-65.c
> new file mode 100644
> index 00000000000..ec1707be9f5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-65.c
> @@ -0,0 +1,15 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-O3" } */
> +/* { dg-additional-options "-mavx2" { target x86_64-*-* i?86-*-* } } */
> +
> +int *a;
> +int b, c, d, e;
> +void f() {
> +  int g;
> +  for (;;)
> +    for (; b;)
> +      if (d)
> +        for (; c;)
> +          if (g)
> +            e += a[1] = a[2] = e;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-66.c b/gcc/testsuite/gcc.dg/vect/bb-slp-66.c
> new file mode 100644
> index 00000000000..b59a2cc7240
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-66.c
> @@ -0,0 +1,32 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-O3" } */
> +
> +typedef struct {
> +  double a, b;
> +} c;
> +typedef struct {
> +  c d;
> +  long coordinates;
> +} e;
> +int f;
> +c g;
> +e h;
> +void k(int);
> +int n();
> +void j() { int i; k(i); }
> +void k(int l) {
> +  double a;
> +  int b;
> +  c m[4];
> +  long i;
> +  for (; l;)
> +    do {
> +      g.a = b ?: a;
> +      m[3] = g;
> +      if (f)
> +        m[0] = m[1] = m[3];
> +      i = 0;
> +      for (; i < 4; i++)
> +        (&h + i)->d = m[i];
> +    } while (n());
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-outer-slp-1.c b/gcc/testsuite/gcc.dg/vect/vect-outer-slp-1.c
> new file mode 100644
> index 00000000000..62b18bd5764
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-outer-slp-1.c
> @@ -0,0 +1,31 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target vect_int } */
> +
> +int a[1024];
> +
> +void foo (void)
> +{
> +  for (int i = 0; i < 1020; i += 4)
> +    {
> +      int suma = a[i];
> +      int sumb = a[i+1];
> +      int sumc = a[i+2];
> +      int sumd = a[i+3];
> +      for (unsigned j = 0; j < 77; ++j)
> +        {
> +          suma = (suma ^ i) + 1;
> +          sumb = (sumb ^ i) + 2;
> +          sumc = (sumc ^ i) + 3;
> +          sumd = (sumd ^ i) + 4;
> +        }
> +      a[i] = suma;
> +      a[i+1] = sumb;
> +      a[i+2] = sumc;
> +      a[i+3] = sumd;
> +    }
> +}
> +
> +/* We should vectorize this outer loop with SLP.  */
> +/* { dg-final { scan-tree-dump "OUTER LOOP VECTORIZED" "vect" } } */
> +/* { dg-final { scan-tree-dump "vectorizing stmts using SLP" "vect" } } */
> +/* { dg-final { scan-tree-dump-not "VEC_PERM_EXPR" "vect" } } */
> diff --git a/gcc/testsuite/gfortran.dg/vect/O3-bb-slp-1.f b/gcc/testsuite/gfortran.dg/vect/O3-bb-slp-1.f
> new file mode 100644
> index 00000000000..74b3b17b5a9
> --- /dev/null
> +++ b/gcc/testsuite/gfortran.dg/vect/O3-bb-slp-1.f
> @@ -0,0 +1,28 @@
> +! { dg-do compile }
> +       subroutine tranx3 (jbeg,jend,kbeg,kend,dlo,den,mflx,zro)
> +      parameter(in =           128+5
> +     &        , jn =           128+5
> +     &        , kn =           128+5)
> +      parameter(ijkn =   128+5)
> +      real*8    zro, dqm, dqp, dx3bi  (kn)
> +      real*8    mflux (ijkn,4), dtwid (ijkn,4),  dd    (ijkn,4)
> +       real*8  mflx (in,jn,kn)
> +       real*8  dlo  (in,jn,kn), den  (in,jn,kn)
> +       do 2100 j=jbeg-1,jend
> +               dtwid (k,1) = ( 0.5 + q1 ) * ( dlo(i  ,j,k-1)
> +     3                     - ( dx3a(k  ) + xi ) * dd   (k  ,1) )
> +               mflux (k,1) = dtwid (k,1) * ( v3(i  ,j,k) - vg3(k) ) * dt
> +             if (j.ge.jbeg) then
> +               den(i  ,j,k) = ( dlo(i  ,j,k) * dvl3a(k)
> +     1                      - etwid (k+1,1) + etwid (k,1) ) * dvl3a i(k)
> +               if (kend .eq. ke) mflx(i  ,j,ke+1) = mflux (ke+1,1)
> +             endif
> +             do 2030 k=max(kbeg-2,ks-1),kend+1
> +               dqm      = (dlo(i  ,j,k  ) - dlo(i  ,j,k-1)) * dx3bi(k  )
> +               dqp      = (dlo(i  ,j,k+1) - dlo(i  ,j,k  )) * dx3bi(k+1)
> +               dd(k,1)  = max ( dqm * dqp, zro )
> +2030       continue
> +               dtwid (k,3) = ( 0.5 + q1 ) * ( dlo(i+2,j,k-1)
> +     3                     - ( dx3a(k  ) + xi ) * deod (k  ,3) )
> +2100   continue
> +       end
> diff --git a/gcc/testsuite/gfortran.dg/vect/O3-bb-slp-2.f b/gcc/testsuite/gfortran.dg/vect/O3-bb-slp-2.f
> new file mode 100644
> index 00000000000..34c44def093
> --- /dev/null
> +++ b/gcc/testsuite/gfortran.dg/vect/O3-bb-slp-2.f
> @@ -0,0 +1,40 @@
> +! { dg-do compile }
> +! { dg-additional-options "-mavx2" { target x86_64-*-* i?86-*-* } }
> +       subroutine tranx3 (ibeg,jbeg,jend,kbeg,kend
> +     &                   ,dlo,den
> +     &                   ,edn)
> +      parameter(in =           128+5
> +     &        , jn =           128+5
> +     &        , kn =           128+5)
> +      parameter(ijkn =   128+5)
> +      real*8   e (in,jn,kn), dqm, dvl3a  (kn), dvl3ai (kn)
> +     &           , dtwid (ijkn,4),  dd    (ijkn,4)
> +     &           , etwid (ijkn,4),  deod  (ijkn,4)
> +       real*8  dlo  (in,jn,kn), den  (in,jn,kn)
> +     &      , edn  (in,jn,kn)
> +       do 2100 j=jbeg-1,jend
> +           i = ibeg - 1
> +               do 1080 k=kbeg,kend
> +               den(i  ,j,k) = ( dlo(i  ,j,k) * dvl3a(k)
> +     1                      - etwid (k+1,1) + etwid (k,1) ) * dvl3a i(k)
> +1080           continue
> +             do 2030 k=max(kbeg-2,ks-1),kend+1
> +               dqm      = (dlo(i+2,j,k  ) - dlo(i+2,j,k-1)) * dx3bi(k  )
> +               dd(k,4)  = max ( dqm * dqp, zro )
> +2030       continue
> +               dtwid (k,3) = ( 0.5 + q1 ) * ( dlo(i+2,j,k-1)
> +     1                     + ( dx3a(k-1) - xi ) * dd   (k-1,3) )
> +     2                     + ( 0.5 - q1 ) * ( dlo(i+2,j,k  )
> +     3                     - ( dx3a(k  ) + xi ) * deod (k  ,3) )
> +               do 2080 k=kbeg,kend
> +               den(i  ,j,k) = ( dlo(i  ,j,k) * dvl3a(k)
> +     1                      - dtwid (k+1,3) + dtwid (k,3) ) * dvl3a i(k)
> +               e  (i+2,j,k) = ( e  (i+2,j,k) * dvl3a(k)
> +     1                      - etwid (k+1,3) + etwid (k,3) ) * dvl3a i(k)
> +               edn(i+2,j,k) =         e(i+2,j,k) / den(i+2,j,k)
> +               e  (i+3,j,k) = ( e  (i+3,j,k) * dvl3a(k)
> +     1                      - etwid (k+1,4) + etwid (k,4) ) * dvl3a i(k)
> +               edn(i+3,j,k) =         e(i+3,j,k) / den(i+3,j,k)
> +2080           continue
> +2100   continue
> +       end
> diff --git a/gcc/tree-vect-loop-manip.c b/gcc/tree-vect-loop-manip.c
> index 5d00b6fb956..36179188f6d 100644
> --- a/gcc/tree-vect-loop-manip.c
> +++ b/gcc/tree-vect-loop-manip.c
> @@ -1084,6 +1084,33 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop,
>    exit = single_exit (loop);
>    basic_block new_preheader = new_bbs[0];
>
> +  /* Before installing PHI arguments make sure that the edges
> +     into them match that of the scalar loop we analyzed.  This
> +     makes sure the SLP tree matches up between the main vectorized
> +     loop and the epilogue vectorized copies.  */
> +  if (single_succ_edge (preheader)->dest_idx
> +      != single_succ_edge (new_bbs[0])->dest_idx)
> +    {
> +      basic_block swap_bb = new_bbs[1];
> +      gcc_assert (EDGE_COUNT (swap_bb->preds) == 2);
> +      std::swap (EDGE_PRED (swap_bb, 0), EDGE_PRED (swap_bb, 1));
> +      EDGE_PRED (swap_bb, 0)->dest_idx = 0;
> +      EDGE_PRED (swap_bb, 1)->dest_idx = 1;
> +    }
> +  if (duplicate_outer_loop)
> +    {
> +      class loop *new_inner_loop = get_loop_copy (scalar_loop->inner);
> +      if (loop_preheader_edge (scalar_loop)->dest_idx
> +         != loop_preheader_edge (new_inner_loop)->dest_idx)
> +       {
> +         basic_block swap_bb = new_inner_loop->header;
> +         gcc_assert (EDGE_COUNT (swap_bb->preds) == 2);
> +         std::swap (EDGE_PRED (swap_bb, 0), EDGE_PRED (swap_bb, 1));
> +         EDGE_PRED (swap_bb, 0)->dest_idx = 0;
> +         EDGE_PRED (swap_bb, 1)->dest_idx = 1;
> +       }
> +    }
> +
>    add_phi_args_after_copy (new_bbs, scalar_loop->num_nodes + 1, NULL);
>
>    /* Skip new preheader since it's deleted if copy loop is added at entry.  */
> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
> index e42f3277ed5..75b731407ba 100644
> --- a/gcc/tree-vect-loop.c
> +++ b/gcc/tree-vect-loop.c
> @@ -7377,15 +7377,24 @@ vect_transform_cycle_phi (loop_vec_info loop_vinfo,
>    if (slp_node)
>      {
>        vec_initial_defs.reserve (vec_num);
> -      gcc_assert (slp_node == slp_node_instance->reduc_phis);
> -      stmt_vec_info first = REDUC_GROUP_FIRST_ELEMENT (reduc_stmt_info);
> -      tree neutral_op
> -       = neutral_op_for_slp_reduction (slp_node, vectype_out,
> -                                       STMT_VINFO_REDUC_CODE (reduc_info),
> -                                       first != NULL);
> -      get_initial_defs_for_reduction (loop_vinfo, slp_node_instance->reduc_phis,
> -                                     &vec_initial_defs, vec_num,
> -                                     first != NULL, neutral_op);
> +      if (nested_cycle)
> +       {
> +         unsigned phi_idx = loop_preheader_edge (loop)->dest_idx;
> +         vect_get_slp_defs (SLP_TREE_CHILDREN (slp_node)[phi_idx],
> +                            &vec_initial_defs);
> +       }
> +      else
> +       {
> +         gcc_assert (slp_node == slp_node_instance->reduc_phis);
> +         stmt_vec_info first = REDUC_GROUP_FIRST_ELEMENT (reduc_stmt_info);
> +         tree neutral_op
> +             = neutral_op_for_slp_reduction (slp_node, vectype_out,
> +                                             STMT_VINFO_REDUC_CODE (reduc_info),
> +                                             first != NULL);
> +         get_initial_defs_for_reduction (loop_vinfo, slp_node_instance->reduc_phis,
> +                                         &vec_initial_defs, vec_num,
> +                                         first != NULL, neutral_op);
> +       }
>      }
>    else
>      {
> @@ -7520,6 +7529,79 @@ vectorizable_lc_phi (loop_vec_info loop_vinfo,
>    return true;
>  }
>
> +/* Vectorizes PHIs.  */
> +
> +bool
> +vectorizable_phi (vec_info *,
> +                 stmt_vec_info stmt_info, gimple **vec_stmt,
> +                 slp_tree slp_node)
> +{
> +  if (!is_a <gphi *> (stmt_info->stmt) || !slp_node)
> +    return false;
> +
> +  if (STMT_VINFO_DEF_TYPE (stmt_info) != vect_internal_def)
> +    return false;
> +
> +  tree vectype = SLP_TREE_VECTYPE (slp_node);
> +
> +  if (!vec_stmt) /* transformation not required.  */
> +    {
> +      slp_tree child;
> +      unsigned i;
> +      FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (slp_node), i, child)
> +       if (!child)
> +         {
> +           if (dump_enabled_p ())
> +             dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> +                              "PHI node with unvectorized backedge def\n");
> +           return false;
> +         }
> +       else if (!vect_maybe_update_slp_op_vectype (child, vectype))
> +         {
> +           if (dump_enabled_p ())
> +             dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> +                              "incompatible vector types for invariants\n");
> +           return false;
> +         }
> +      STMT_VINFO_TYPE (stmt_info) = phi_info_type;
> +      return true;
> +    }
> +
> +  tree scalar_dest = gimple_phi_result (stmt_info->stmt);
> +  basic_block bb = gimple_bb (stmt_info->stmt);
> +  tree vec_dest = vect_create_destination_var (scalar_dest, vectype);
> +  auto_vec<tree> vec_oprnds;
> +  auto_vec<gphi *> new_phis;
> +  for (unsigned i = 0; i < gimple_phi_num_args (stmt_info->stmt); ++i)
> +    {
> +      slp_tree child = SLP_TREE_CHILDREN (slp_node)[i];
> +
> +      /* Skip not yet vectorized defs.  */
> +      if (SLP_TREE_DEF_TYPE (child) == vect_internal_def
> +         && SLP_TREE_VEC_STMTS (child).is_empty ())
> +       continue;
> +
> +      vect_get_slp_defs (SLP_TREE_CHILDREN (slp_node)[i], &vec_oprnds);
> +      if (!new_phis.exists ())
> +       {
> +         new_phis.create (vec_oprnds.length ());
> +         for (unsigned j = 0; j < vec_oprnds.length (); j++)
> +           {
> +             /* Create the vectorized LC PHI node.  */
> +             new_phis.quick_push (create_phi_node (vec_dest, bb));
> +             SLP_TREE_VEC_STMTS (slp_node).quick_push (new_phis[j]);
> +           }
> +       }
> +      edge e = gimple_phi_arg_edge (as_a <gphi *> (stmt_info->stmt), i);
> +      for (unsigned j = 0; j < vec_oprnds.length (); j++)
> +       add_phi_arg (new_phis[j], vec_oprnds[j], e, UNKNOWN_LOCATION);
> +    }
> +  /* We should have at least one already vectorized child.  */
> +  gcc_assert (new_phis.exists ());
> +
> +  return true;
> +}
> +
>
>  /* Function vect_min_worthwhile_factor.
>
> @@ -8376,8 +8458,16 @@ vectorizable_live_operation (vec_info *vinfo,
>        gimple_seq stmts = NULL;
>        new_tree = force_gimple_operand (fold_convert (lhs_type, new_tree),
>                                        &stmts, true, NULL_TREE);
> -
> -      gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
> +      if (is_a <gphi *> (vec_stmt))
> +       {
> +         gimple_stmt_iterator si = gsi_after_labels (gimple_bb (vec_stmt));
> +         gsi_insert_seq_before (&si, stmts, GSI_SAME_STMT);
> +       }
> +      else
> +       {
> +         gimple_stmt_iterator si = gsi_for_stmt (vec_stmt);
> +         gsi_insert_seq_after (&si, stmts, GSI_SAME_STMT);
> +       }
>
>        /* Replace use of lhs with newly computed result.  If the use stmt is a
>          single arg PHI, just replace all uses of PHI result.  It's necessary
> diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
> index 85865dae1ab..f544b552a46 100644
> --- a/gcc/tree-vect-slp.c
> +++ b/gcc/tree-vect-slp.c
> @@ -115,7 +115,8 @@ vect_free_slp_tree (slp_tree node)
>      return;
>
>    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    vect_free_slp_tree (child);
> +    if (child)
> +      vect_free_slp_tree (child);
>
>    delete node;
>  }
> @@ -148,9 +149,9 @@ vect_free_slp_instance (slp_instance instance)
>  /* Create an SLP node for SCALAR_STMTS.  */
>
>  static slp_tree
> -vect_create_new_slp_node (vec<stmt_vec_info> scalar_stmts, unsigned nops)
> +vect_create_new_slp_node (slp_tree node,
> +                         vec<stmt_vec_info> scalar_stmts, unsigned nops)
>  {
> -  slp_tree node = new _slp_tree;
>    SLP_TREE_SCALAR_STMTS (node) = scalar_stmts;
>    SLP_TREE_CHILDREN (node).create (nops);
>    SLP_TREE_DEF_TYPE (node) = vect_internal_def;
> @@ -159,18 +160,33 @@ vect_create_new_slp_node (vec<stmt_vec_info> scalar_stmts, unsigned nops)
>    return node;
>  }
>
> +/* Create an SLP node for SCALAR_STMTS.  */
> +
> +static slp_tree
> +vect_create_new_slp_node (vec<stmt_vec_info> scalar_stmts, unsigned nops)
> +{
> +  return vect_create_new_slp_node (new _slp_tree, scalar_stmts, nops);
> +}
> +
>  /* Create an SLP node for OPS.  */
>
>  static slp_tree
> -vect_create_new_slp_node (vec<tree> ops)
> +vect_create_new_slp_node (slp_tree node, vec<tree> ops)
>  {
> -  slp_tree node = new _slp_tree;
>    SLP_TREE_SCALAR_OPS (node) = ops;
>    SLP_TREE_DEF_TYPE (node) = vect_external_def;
>    SLP_TREE_LANES (node) = ops.length ();
>    return node;
>  }
>
> +/* Create an SLP node for OPS.  */
> +
> +static slp_tree
> +vect_create_new_slp_node (vec<tree> ops)
> +{
> +  return vect_create_new_slp_node (new _slp_tree, ops);
> +}
> +
>
>  /* This structure is used in creation of an SLP tree.  Each instance
>     corresponds to the same operand in a group of scalar stmts in an SLP
> @@ -443,10 +459,13 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
>        else
>         commutative_op = commutative_tree_code (code) ? 0U : -1U;
>      }
> +  else if (gphi *stmt = dyn_cast <gphi *> (stmt_info->stmt))
> +    number_of_oprnds = gimple_phi_num_args (stmt);
>    else
>      return -1;
>
>    bool swapped = (swap != 0);
> +  bool backedge = false;
>    gcc_assert (!swapped || first_op_cond);
>    enum vect_def_type *dts = XALLOCAVEC (enum vect_def_type, number_of_oprnds);
>    for (i = 0; i < number_of_oprnds; i++)
> @@ -463,6 +482,13 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
>           else
>             oprnd = gimple_op (stmt_info->stmt, map[i]);
>         }
> +      else if (gphi *stmt = dyn_cast <gphi *> (stmt_info->stmt))
> +       {
> +         oprnd = gimple_phi_arg_def (stmt, i);
> +         backedge = dominated_by_p (CDI_DOMINATORS,
> +                                    gimple_phi_arg_edge (stmt, i)->src,
> +                                    gimple_bb (stmt_info->stmt));
> +       }
>        else
>         oprnd = gimple_op (stmt_info->stmt, first_op_idx + (swapped ? !i : i));
>        if (TREE_CODE (oprnd) == VIEW_CONVERT_EXPR)
> @@ -487,6 +513,26 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
>        oprnd_info->def_stmts.quick_push (def_stmt_info);
>        oprnd_info->ops.quick_push (oprnd);
>
> +      /* If there's a extern def on a backedge make sure we can
> +        code-generate at the region start.
> +        ???  This is another case that could be fixed by adjusting
> +        how we split the function but at the moment we'd have conflicting
> +        goals there.  */
> +      if (backedge
> +         && dts[i] == vect_external_def
> +         && is_a <bb_vec_info> (vinfo)
> +         && !SSA_NAME_IS_DEFAULT_DEF (oprnd)
> +         && !dominated_by_p (CDI_DOMINATORS,
> +                             as_a <bb_vec_info> (vinfo)->bbs[0],
> +                             gimple_bb (SSA_NAME_DEF_STMT (oprnd))))
> +       {
> +         if (dump_enabled_p ())
> +           dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> +                            "Build SLP failed: extern def %T only defined "
> +                            "on backedge\n", oprnd);
> +         return -1;
> +       }
> +
>        if (first)
>         {
>           tree type = TREE_TYPE (oprnd);
> @@ -521,6 +567,7 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
>             case vect_internal_def:
>             case vect_reduction_def:
>             case vect_induction_def:
> +           case vect_nested_cycle:
>               break;
>
>             default:
> @@ -815,6 +862,7 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char *swap,
>    machine_mode vec_mode;
>    stmt_vec_info first_load = NULL, prev_first_load = NULL;
>    bool first_stmt_load_p = false, load_p = false;
> +  bool first_stmt_phi_p = false, phi_p = false;
>
>    /* For every stmt in NODE find its def stmt/s.  */
>    stmt_vec_info stmt_info;
> @@ -904,6 +952,11 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char *swap,
>               return false;
>             }
>         }
> +      else if (gimple_code (stmt) == GIMPLE_PHI)
> +       {
> +         rhs_code = ERROR_MARK;
> +         phi_p = true;
> +       }
>        else
>         {
>           rhs_code = gimple_assign_rhs_code (stmt);
> @@ -916,6 +969,7 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char *swap,
>           *node_vectype = vectype;
>           first_stmt_code = rhs_code;
>           first_stmt_load_p = load_p;
> +         first_stmt_phi_p = phi_p;
>
>           /* Shift arguments should be equal in all the packed stmts for a
>              vector shift with scalar shift operand.  */
> @@ -1021,7 +1075,8 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char *swap,
>                         || first_stmt_code == INDIRECT_REF
>                         || first_stmt_code == COMPONENT_REF
>                         || first_stmt_code == MEM_REF)))
> -             || first_stmt_load_p != load_p)
> +             || first_stmt_load_p != load_p
> +             || first_stmt_phi_p != phi_p)
>             {
>               if (dump_enabled_p ())
>                 {
> @@ -1077,6 +1132,18 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char *swap,
>                 }
>             }
>
> +         if (phi_p
> +             && (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);
> +             /* Mismatch.  */
> +             continue;
> +           }
> +
>           if (!types_compatible_p (vectype, *node_vectype))
>             {
>               if (dump_enabled_p ())
> @@ -1138,7 +1205,8 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char *swap,
>             }
>
>           /* Not memory operation.  */
> -         if (TREE_CODE_CLASS (rhs_code) != tcc_binary
> +         if (!phi_p
> +             && TREE_CODE_CLASS (rhs_code) != tcc_binary
>               && TREE_CODE_CLASS (rhs_code) != tcc_unary
>               && TREE_CODE_CLASS (rhs_code) != tcc_expression
>               && TREE_CODE_CLASS (rhs_code) != tcc_comparison
> @@ -1251,7 +1319,7 @@ typedef hash_map <vec <gimple *>, slp_tree,
>    scalar_stmts_to_slp_tree_map_t;
>
>  static slp_tree
> -vect_build_slp_tree_2 (vec_info *vinfo,
> +vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
>                        vec<stmt_vec_info> stmts, unsigned int group_size,
>                        poly_uint64 *max_nunits,
>                        bool *matches, unsigned *npermutes, unsigned *tree_size,
> @@ -1276,19 +1344,37 @@ vect_build_slp_tree (vec_info *vinfo,
>         }
>        return *leader;
>      }
> +
> +  /* Seed the bst_map with a stub node to be filled by vect_build_slp_tree_2
> +     so we can pick up backedge destinations during discovery.  */
> +  slp_tree res = new _slp_tree;
> +  SLP_TREE_DEF_TYPE (res) = vect_internal_def;
> +  SLP_TREE_SCALAR_STMTS (res) = stmts;
> +  bst_map->put (stmts.copy (), res);
> +
>    poly_uint64 this_max_nunits = 1;
> -  slp_tree res = vect_build_slp_tree_2 (vinfo, stmts, group_size,
> +  slp_tree res_ = vect_build_slp_tree_2 (vinfo, res, stmts, group_size,
>                                         &this_max_nunits,
>                                         matches, npermutes, tree_size, bst_map);
> -  if (res)
> +  if (!res_)
> +    {
> +      bool existed_p = bst_map->put (stmts, NULL);
> +      gcc_assert (existed_p);
> +      /* Mark the node invalid so we can detect those when still in use
> +        as backedge destinations.  */
> +      SLP_TREE_SCALAR_STMTS (res) = vNULL;
> +      SLP_TREE_DEF_TYPE (res) = vect_uninitialized_def;
> +      vect_free_slp_tree (res);
> +    }
> +  else
>      {
> +      gcc_assert (res_ == res);
>        res->max_nunits = this_max_nunits;
>        vect_update_max_nunits (max_nunits, this_max_nunits);
>        /* Keep a reference for the bst_map use.  */
>        SLP_TREE_REF_COUNT (res)++;
>      }
> -  bst_map->put (stmts.copy (), res);
> -  return res;
> +  return res_;
>  }
>
>  /* Recursively build an SLP tree starting from NODE.
> @@ -1299,7 +1385,7 @@ vect_build_slp_tree (vec_info *vinfo,
>     was found.  */
>
>  static slp_tree
> -vect_build_slp_tree_2 (vec_info *vinfo,
> +vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
>                        vec<stmt_vec_info> stmts, unsigned int group_size,
>                        poly_uint64 *max_nunits,
>                        bool *matches, unsigned *npermutes, unsigned *tree_size,
> @@ -1307,7 +1393,6 @@ vect_build_slp_tree_2 (vec_info *vinfo,
>  {
>    unsigned nops, i, this_tree_size = 0;
>    poly_uint64 this_max_nunits = *max_nunits;
> -  slp_tree node;
>
>    matches[0] = false;
>
> @@ -1327,41 +1412,60 @@ vect_build_slp_tree_2 (vec_info *vinfo,
>
>    /* If the SLP node is a PHI (induction or reduction), terminate
>       the recursion.  */
> -  if (gphi *stmt = dyn_cast <gphi *> (stmt_info->stmt))
> -    {
> -      tree scalar_type = TREE_TYPE (PHI_RESULT (stmt));
> -      tree vectype = get_vectype_for_scalar_type (vinfo, scalar_type,
> -                                                 group_size);
> -      if (!vect_record_max_nunits (vinfo, stmt_info, group_size, vectype,
> -                                  max_nunits))
> -       return NULL;
> +  bool skip_args[2] = { false, false };
> +  if (loop_vec_info loop_vinfo = dyn_cast <loop_vec_info> (vinfo))
> +    if (gphi *stmt = dyn_cast <gphi *> (stmt_info->stmt))
> +      {
> +       tree scalar_type = TREE_TYPE (PHI_RESULT (stmt));
> +       tree vectype = get_vectype_for_scalar_type (vinfo, scalar_type,
> +                                                   group_size);
> +       if (!vect_record_max_nunits (vinfo, stmt_info, group_size, vectype,
> +                                    max_nunits))
> +         return NULL;
>
> -      vect_def_type def_type = STMT_VINFO_DEF_TYPE (stmt_info);
> -      /* Induction from different IVs is not supported.  */
> -      if (def_type == vect_induction_def)
> -       {
> -         stmt_vec_info other_info;
> -         FOR_EACH_VEC_ELT (stmts, i, other_info)
> -           if (stmt_info != other_info)
> -             return NULL;
> -       }
> -      else if (def_type == vect_reduction_def
> -              || def_type == vect_double_reduction_def
> -              || def_type == vect_nested_cycle)
> -       {
> -         /* Else def types have to match.  */
> -         stmt_vec_info other_info;
> -         FOR_EACH_VEC_ELT (stmts, i, other_info)
> -           if (STMT_VINFO_DEF_TYPE (other_info) != def_type)
> -             return NULL;
> -       }
> -      else
> -       return NULL;
> -      (*tree_size)++;
> -      node = vect_create_new_slp_node (stmts, nops);
> -      SLP_TREE_VECTYPE (node) = vectype;
> -      return node;
> -    }
> +       vect_def_type def_type = STMT_VINFO_DEF_TYPE (stmt_info);
> +       /* Induction from different IVs is not supported.  */
> +       if (def_type == vect_induction_def)
> +         {
> +           stmt_vec_info other_info;
> +           FOR_EACH_VEC_ELT (stmts, i, other_info)
> +             if (stmt_info != other_info)
> +               return NULL;
> +
> +           /* Induction PHIs are leafs.  */
> +           (*tree_size)++;
> +           node = vect_create_new_slp_node (node, stmts, nops);
> +           SLP_TREE_VECTYPE (node) = vectype;
> +           SLP_TREE_CHILDREN (node).quick_grow_cleared (nops);
> +           return node;
> +         }
> +       else if (def_type == vect_reduction_def
> +                || def_type == vect_double_reduction_def
> +                || def_type == vect_nested_cycle)
> +         {
> +           /* Else def types have to match.  */
> +           stmt_vec_info other_info;
> +           bool all_same = true;
> +           FOR_EACH_VEC_ELT (stmts, i, other_info)
> +             {
> +               if (STMT_VINFO_DEF_TYPE (other_info) != def_type)
> +                 return NULL;
> +               if (other_info != stmt_info)
> +                 all_same = false;
> +             }
> +           class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
> +           /* Reduction initial values are not explicitely represented.  */
> +           if (!nested_in_vect_loop_p (loop, stmt_info))
> +             skip_args[loop_preheader_edge (loop)->dest_idx] = true;
> +           /* Reduction chain backedge defs are filled manually.
> +              ???  Need a better way to identify a SLP reduction chain PHI.
> +              Or a better overall way to SLP match those.  */
> +           if (all_same && def_type == vect_reduction_def)
> +             skip_args[loop_latch_edge (loop)->dest_idx] = true;
> +         }
> +       else if (def_type != vect_internal_def)
> +         return NULL;
> +      }
>
>
>    bool two_operators = false;
> @@ -1386,7 +1490,7 @@ vect_build_slp_tree_2 (vec_info *vinfo,
>         {
>           *max_nunits = this_max_nunits;
>           (*tree_size)++;
> -         node = vect_create_new_slp_node (stmts, 0);
> +         node = vect_create_new_slp_node (node, stmts, 0);
>           SLP_TREE_VECTYPE (node) = vectype;
>           /* And compute the load permutation.  Whether it is actually
>              a permutation depends on the unrolling factor which is
> @@ -1440,7 +1544,7 @@ vect_build_slp_tree_2 (vec_info *vinfo,
>          representing an actual vector without any scalar ops.
>          ???  We could hide it completely with making the permute node
>          external?  */
> -      node = vect_create_new_slp_node (stmts, 1);
> +      node = vect_create_new_slp_node (node, stmts, 1);
>        SLP_TREE_CODE (node) = VEC_PERM_EXPR;
>        SLP_TREE_LANE_PERMUTATION (node) = lperm;
>        SLP_TREE_VECTYPE (node) = vectype;
> @@ -1486,6 +1590,14 @@ vect_build_slp_tree_2 (vec_info *vinfo,
>           continue;
>         }
>
> +      /* We're skipping certain operands from processing, for example
> +        outer loop reduction initial defs.  */
> +      if (i <= 1 && skip_args[i])
> +       {
> +         children.safe_push (NULL);
> +         continue;
> +       }
> +
>        if (is_a <bb_vec_info> (vinfo)
>           && oprnd_info->first_dt == vect_internal_def)
>         {
> @@ -1508,9 +1620,8 @@ vect_build_slp_tree_2 (vec_info *vinfo,
>             }
>         }
>
> -      if (oprnd_info->first_dt != vect_internal_def
> -         && oprnd_info->first_dt != vect_reduction_def
> -         && oprnd_info->first_dt != vect_induction_def)
> +      if (oprnd_info->first_dt == vect_external_def
> +         || oprnd_info->first_dt == vect_constant_def)
>         {
>           slp_tree invnode = vect_create_new_slp_node (oprnd_info->ops);
>           SLP_TREE_DEF_TYPE (invnode) = oprnd_info->first_dt;
> @@ -1639,14 +1750,14 @@ fail:
>               child = vect_create_new_slp_node (oprnd_info->ops);
>               children.safe_push (child);
>               oprnd_info->ops = vNULL;
> -             oprnd_info->def_stmts = vNULL;
>               continue;
>             }
>         }
>
>        gcc_assert (child == NULL);
>        FOR_EACH_VEC_ELT (children, j, child)
> -       vect_free_slp_tree (child);
> +       if (child)
> +         vect_free_slp_tree (child);
>        vect_free_oprnd_info (oprnds_info);
>        return NULL;
>      }
> @@ -1670,7 +1781,9 @@ fail:
>        unsigned n_vector_builds = 0;
>        FOR_EACH_VEC_ELT (children, j, child)
>         {
> -         if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
> +         if (!child)
> +           ;
> +         else if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
>             all_uniform_p = false;
>           else if (!vect_slp_tree_uniform_p (child))
>             {
> @@ -1684,7 +1797,8 @@ fail:
>           /* Roll back.  */
>           matches[0] = false;
>           FOR_EACH_VEC_ELT (children, j, child)
> -           vect_free_slp_tree (child);
> +           if (child)
> +             vect_free_slp_tree (child);
>
>           if (dump_enabled_p ())
>             dump_printf_loc (MSG_NOTE, vect_location,
> @@ -1718,7 +1832,7 @@ fail:
>
>        /* Here we record the original defs since this
>          node represents the final lane configuration.  */
> -      node = vect_create_new_slp_node (stmts, 2);
> +      node = vect_create_new_slp_node (node, stmts, 2);
>        SLP_TREE_VECTYPE (node) = vectype;
>        SLP_TREE_CODE (node) = VEC_PERM_EXPR;
>        SLP_TREE_CHILDREN (node).quick_push (one);
> @@ -1749,7 +1863,7 @@ fail:
>        return node;
>      }
>
> -  node = vect_create_new_slp_node (stmts, nops);
> +  node = vect_create_new_slp_node (node, stmts, nops);
>    SLP_TREE_VECTYPE (node) = vectype;
>    SLP_TREE_CHILDREN (node).splice (children);
>    return node;
> @@ -1835,7 +1949,8 @@ vect_print_slp_graph (dump_flags_t dump_kind, dump_location_t loc,
>    vect_print_slp_tree (dump_kind, loc, node);
>
>    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    vect_print_slp_graph (dump_kind, loc, child, visited);
> +    if (child)
> +      vect_print_slp_graph (dump_kind, loc, child, visited);
>  }
>
>  static void
> @@ -1865,7 +1980,8 @@ vect_mark_slp_stmts (slp_tree node, hash_set<slp_tree> &visited)
>      STMT_SLP_TYPE (stmt_info) = pure_slp;
>
>    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    vect_mark_slp_stmts (child, visited);
> +    if (child)
> +      vect_mark_slp_stmts (child, visited);
>  }
>
>  static void
> @@ -1898,7 +2014,8 @@ vect_mark_slp_stmts_relevant (slp_tree node, hash_set<slp_tree> &visited)
>      }
>
>    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    vect_mark_slp_stmts_relevant (child, visited);
> +    if (child)
> +      vect_mark_slp_stmts_relevant (child, visited);
>  }
>
>  static void
> @@ -1915,7 +2032,7 @@ static void
>  vect_gather_slp_loads (vec<slp_tree> &loads, slp_tree node,
>                        hash_set<slp_tree> &visited)
>  {
> -  if (visited.add (node))
> +  if (!node || visited.add (node))
>      return;
>
>    if (SLP_TREE_CHILDREN (node).length () == 0)
> @@ -2176,34 +2293,62 @@ vect_build_slp_instance (vec_info *vinfo,
>                 }
>             }
>
> -         /* If this is a reduction chain with a conversion in front
> -            amend the SLP tree with a node for that.  */
> -         if (kind == slp_inst_kind_reduc_chain
> -             && STMT_VINFO_DEF_TYPE (scalar_stmts[0]) != vect_reduction_def)
> +         /* Fixup SLP reduction chains.  */
> +         if (kind == slp_inst_kind_reduc_chain)
>             {
> -             /* Get at the conversion stmt - we know it's the single use
> -                of the last stmt of the reduction chain.  */
> -             gimple *tem = vect_orig_stmt (scalar_stmts[group_size - 1])->stmt;
> +             /* If this is a reduction chain with a conversion in front
> +                amend the SLP tree with a node for that.  */
> +             gimple *scalar_def
> +               = vect_orig_stmt (scalar_stmts[group_size - 1])->stmt;
> +             if (STMT_VINFO_DEF_TYPE (scalar_stmts[0]) != vect_reduction_def)
> +               {
> +                 /* Get at the conversion stmt - we know it's the single use
> +                    of the last stmt of the reduction chain.  */
> +                 use_operand_p use_p;
> +                 bool r = single_imm_use (gimple_assign_lhs (scalar_def),
> +                                          &use_p, &scalar_def);
> +                 gcc_assert (r);
> +                 stmt_vec_info next_info = vinfo->lookup_stmt (scalar_def);
> +                 next_info = vect_stmt_to_vectorize (next_info);
> +                 scalar_stmts = vNULL;
> +                 scalar_stmts.create (group_size);
> +                 for (unsigned i = 0; i < group_size; ++i)
> +                   scalar_stmts.quick_push (next_info);
> +                 slp_tree conv = vect_create_new_slp_node (scalar_stmts, 1);
> +                 SLP_TREE_VECTYPE (conv) = STMT_VINFO_VECTYPE (next_info);
> +                 SLP_TREE_CHILDREN (conv).quick_push (node);
> +                 SLP_INSTANCE_TREE (new_instance) = conv;
> +                 /* We also have to fake this conversion stmt as SLP reduction
> +                    group so we don't have to mess with too much code
> +                    elsewhere.  */
> +                 REDUC_GROUP_FIRST_ELEMENT (next_info) = next_info;
> +                 REDUC_GROUP_NEXT_ELEMENT (next_info) = NULL;
> +               }
> +             /* Fill the backedge child of the PHI SLP node.  The
> +                general matching code cannot find it because the
> +                scalar code does not reflect how we vectorize the
> +                reduction.  */
>               use_operand_p use_p;
> -             gimple *use_stmt;
> -             bool r = single_imm_use (gimple_assign_lhs (tem),
> -                                      &use_p, &use_stmt);
> -             gcc_assert (r);
> -             stmt_vec_info next_info = vinfo->lookup_stmt (use_stmt);
> -             next_info = vect_stmt_to_vectorize (next_info);
> -             scalar_stmts = vNULL;
> -             scalar_stmts.create (group_size);
> -             for (unsigned i = 0; i < group_size; ++i)
> -               scalar_stmts.quick_push (next_info);
> -             slp_tree conv = vect_create_new_slp_node (scalar_stmts, 1);
> -             SLP_TREE_VECTYPE (conv) = STMT_VINFO_VECTYPE (next_info);
> -             SLP_TREE_CHILDREN (conv).quick_push (node);
> -             SLP_INSTANCE_TREE (new_instance) = conv;
> -             /* We also have to fake this conversion stmt as SLP reduction
> -                group so we don't have to mess with too much code
> -                elsewhere.  */
> -             REDUC_GROUP_FIRST_ELEMENT (next_info) = next_info;
> -             REDUC_GROUP_NEXT_ELEMENT (next_info) = NULL;
> +             imm_use_iterator imm_iter;
> +             class loop *loop = LOOP_VINFO_LOOP (as_a <loop_vec_info> (vinfo));
> +             FOR_EACH_IMM_USE_FAST (use_p, imm_iter,
> +                                    gimple_get_lhs (scalar_def))
> +               /* There are exactly two non-debug uses, the reduction
> +                  PHI and the loop-closed PHI node.  */
> +               if (!is_gimple_debug (USE_STMT (use_p))
> +                   && gimple_bb (USE_STMT (use_p)) == loop->header)
> +                 {
> +                   auto_vec<stmt_vec_info, 64> phis (group_size);
> +                   stmt_vec_info phi_info
> +                     = vinfo->lookup_stmt (USE_STMT (use_p));
> +                   for (unsigned i = 0; i < group_size; ++i)
> +                     phis.quick_push (phi_info);
> +                   slp_tree *phi_node = bst_map->get (phis);
> +                   unsigned dest_idx = loop_latch_edge (loop)->dest_idx;
> +                   SLP_TREE_CHILDREN (*phi_node)[dest_idx]
> +                     = SLP_INSTANCE_TREE (new_instance);
> +                   SLP_INSTANCE_TREE (new_instance)->refcnt++;
> +                 }
>             }
>
>           vinfo->slp_instances.safe_push (new_instance);
> @@ -2437,60 +2582,6 @@ vect_analyze_slp_instance (vec_info *vinfo,
>    return res;
>  }
>
> -/* Fill in backedge SLP children in the SLP graph.  */
> -
> -static void
> -vect_analyze_slp_backedges (vec_info *vinfo, slp_tree node,
> -                           scalar_stmts_to_slp_tree_map_t *bst_map,
> -                           hash_set<slp_tree> &visited)
> -{
> -  if (SLP_TREE_DEF_TYPE (node) != vect_internal_def
> -      || visited.add (node))
> -    return;
> -
> -  slp_tree child;
> -  unsigned i;
> -  FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    if (child)
> -      vect_analyze_slp_backedges (vinfo, child, bst_map, visited);
> -
> -  /* Inductions are not vectorized by vectorizing their defining cycle
> -     but by materializing the values from SCEV data.  */
> -  if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (node))
> -      == vect_induction_def)
> -    return;
> -
> -  if (gphi *phi = dyn_cast <gphi *> (SLP_TREE_REPRESENTATIVE (node)->stmt))
> -    for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
> -      {
> -       auto_vec<stmt_vec_info, 64> stmts;
> -       unsigned j;
> -       stmt_vec_info phi_info;
> -       FOR_EACH_VEC_ELT (SLP_TREE_SCALAR_STMTS (node), j, phi_info)
> -         {
> -           tree def = gimple_phi_arg_def (as_a <gphi *>(phi_info->stmt), i);
> -           stmt_vec_info def_info = vinfo->lookup_def (def);
> -           if (!def_info)
> -             break;
> -           stmts.safe_push (vect_stmt_to_vectorize (def_info));
> -         }
> -       if (j != SLP_TREE_LANES (node))
> -         continue;
> -       slp_tree *edge_def = bst_map->get (stmts);
> -       if (edge_def)
> -         {
> -           /* ???  We're currently not recording non-backedge children
> -              of PHIs like external reduction initial values.  Avoid
> -              NULL entries in SLP_TREE_CHILDREN for those and thus
> -              for now simply only record backedge defs at a
> -              SLP_TREE_CHILDREN index possibly not matching that of
> -              the corresponding PHI argument index.  */
> -           SLP_TREE_CHILDREN (node).quick_push (*edge_def);
> -           (*edge_def)->refcnt++;
> -         }
> -      }
> -}
> -
>  /* Check if there are stmts in the loop can be vectorized using SLP.  Build SLP
>     trees of packed scalar stmts if SLP is possible.  */
>
> @@ -2541,13 +2632,6 @@ vect_analyze_slp (vec_info *vinfo, unsigned max_tree_size)
>                                    max_tree_size);
>      }
>
> -  /* Fill in backedges.  */
> -  slp_instance instance;
> -  hash_set<slp_tree> visited;
> -  FOR_EACH_VEC_ELT (vinfo->slp_instances, i, instance)
> -    vect_analyze_slp_backedges (vinfo, SLP_INSTANCE_TREE (instance),
> -                               bst_map, visited);
> -
>    /* The map keeps a reference on SLP nodes built, release that.  */
>    for (scalar_stmts_to_slp_tree_map_t::iterator it = bst_map->begin ();
>         it != bst_map->end (); ++it)
> @@ -2572,11 +2656,16 @@ vect_slp_build_vertices (hash_set<slp_tree> &visited, slp_tree node,
>
>    node->vertex = vertices.length ();
>    vertices.safe_push (node);
> -  if (SLP_TREE_CHILDREN (node).is_empty ())
> +
> +  bool leaf = true;
> +  FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> +    if (child)
> +      {
> +       leaf = false;
> +       vect_slp_build_vertices (visited, child, vertices, leafs);
> +      }
> +  if (leaf)
>      leafs.safe_push (node->vertex);
> -  else
> -    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -      vect_slp_build_vertices (visited, child, vertices, leafs);
>  }
>
>  /* Fill the vertices and leafs vector with all nodes in the SLP graph.  */
> @@ -2654,7 +2743,8 @@ vect_optimize_slp (vec_info *vinfo)
>        unsigned j;
>        slp_tree child;
>        FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), j, child)
> -       add_edge (slpg, i, child->vertex);
> +       if (child)
> +         add_edge (slpg, i, child->vertex);
>      }
>
>    /* Compute (reverse) postorder on the inverted graph.  */
> @@ -2853,7 +2943,7 @@ vect_optimize_slp (vec_info *vinfo)
>        slp_tree child;
>        FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), j, child)
>         {
> -         if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
> +         if (!child || SLP_TREE_DEF_TYPE (child) == vect_internal_def)
>             continue;
>
>           /* If the vector is uniform there's nothing to do.  */
> @@ -3291,6 +3381,7 @@ vect_slp_convert_to_external (vec_info *vinfo, slp_tree node,
>    unsigned int group_size = SLP_TREE_LANES (node);
>    SLP_TREE_DEF_TYPE (node) = vect_external_def;
>    SLP_TREE_SCALAR_OPS (node).safe_grow (group_size, true);
> +  SLP_TREE_LOAD_PERMUTATION (node).release ();
>    FOR_EACH_VEC_ELT (SLP_TREE_SCALAR_STMTS (node), i, stmt_info)
>      {
>        tree lhs = gimple_get_lhs (vect_orig_stmt (stmt_info)->stmt);
> @@ -3373,9 +3464,20 @@ vect_slp_analyze_node_operations (vec_info *vinfo, slp_tree node,
>    slp_tree child;
>
>    /* Assume we can code-generate all invariants.  */
> -  if (SLP_TREE_DEF_TYPE (node) != vect_internal_def)
> +  if (!node
> +      || SLP_TREE_DEF_TYPE (node) == vect_constant_def
> +      || SLP_TREE_DEF_TYPE (node) == vect_external_def)
>      return true;
>
> +  if (SLP_TREE_DEF_TYPE (node) == vect_uninitialized_def)
> +    {
> +      if (dump_enabled_p ())
> +       dump_printf_loc (MSG_NOTE, vect_location,
> +                        "Failed cyclic SLP reference in %p", node);
> +      return false;
> +    }
> +  gcc_assert (SLP_TREE_DEF_TYPE (node) == vect_internal_def);
> +
>    /* If we already analyzed the exact same set of scalar stmts we're done.
>       We share the generated vector stmts for those.  */
>    if (visited.contains (node)
> @@ -3404,8 +3506,9 @@ vect_slp_analyze_node_operations (vec_info *vinfo, slp_tree node,
>       other referrers.  */
>    if (res)
>      FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), j, child)
> -      if ((SLP_TREE_DEF_TYPE (child) == vect_constant_def
> -          || SLP_TREE_DEF_TYPE (child) == vect_external_def)
> +      if (child
> +         && (SLP_TREE_DEF_TYPE (child) == vect_constant_def
> +             || SLP_TREE_DEF_TYPE (child) == vect_external_def)
>           /* Perform usual caching, note code-generation still
>              code-gens these nodes multiple times but we expect
>              to CSE them later.  */
> @@ -3459,8 +3562,12 @@ static void
>  vect_bb_slp_mark_live_stmts (bb_vec_info bb_vinfo, slp_tree node,
>                              slp_instance instance,
>                              stmt_vector_for_cost *cost_vec,
> -                            hash_set<stmt_vec_info> &svisited)
> +                            hash_set<stmt_vec_info> &svisited,
> +                            hash_set<slp_tree> &visited)
>  {
> +  if (visited.add (node))
> +    return;
> +
>    unsigned i;
>    stmt_vec_info stmt_info;
>    stmt_vec_info last_stmt = vect_find_last_scalar_stmt_in_slp (node);
> @@ -3479,7 +3586,7 @@ vect_bb_slp_mark_live_stmts (bb_vec_info bb_vinfo, slp_tree node,
>        gimple *orig_stmt = orig_stmt_info->stmt;
>        ssa_op_iter op_iter;
>        def_operand_p def_p;
> -      FOR_EACH_SSA_DEF_OPERAND (def_p, orig_stmt, op_iter, SSA_OP_DEF)
> +      FOR_EACH_PHI_OR_STMT_DEF (def_p, orig_stmt, op_iter, SSA_OP_DEF)
>         {
>           imm_use_iterator use_iter;
>           gimple *use_stmt;
> @@ -3548,9 +3655,9 @@ vect_bb_slp_mark_live_stmts (bb_vec_info bb_vinfo, slp_tree node,
>
>    slp_tree child;
>    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
> +    if (child && SLP_TREE_DEF_TYPE (child) == vect_internal_def)
>        vect_bb_slp_mark_live_stmts (bb_vinfo, child, instance,
> -                                  cost_vec, svisited);
> +                                  cost_vec, svisited, visited);
>  }
>
>  /* Analyze statements in SLP instances of VINFO.  Return true if the
> @@ -3615,11 +3722,13 @@ vect_slp_analyze_operations (vec_info *vinfo)
>    if (bb_vec_info bb_vinfo = dyn_cast <bb_vec_info> (vinfo))
>      {
>        hash_set<stmt_vec_info> svisited;
> +      hash_set<slp_tree> visited;
>        for (i = 0; vinfo->slp_instances.iterate (i, &instance); ++i)
>         {
>           vect_location = instance->location ();
>           vect_bb_slp_mark_live_stmts (bb_vinfo, SLP_INSTANCE_TREE (instance),
> -                                      instance, &instance->cost_vec, svisited);
> +                                      instance, &instance->cost_vec, svisited,
> +                                      visited);
>         }
>      }
>
> @@ -3683,7 +3792,7 @@ vect_bb_partition_graph_r (bb_vec_info bb_vinfo,
>
>    slp_tree child;
>    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
> +    if (child && SLP_TREE_DEF_TYPE (child) == vect_internal_def)
>        vect_bb_partition_graph_r (bb_vinfo, instance, child, stmt_to_instance,
>                                  instance_leader, visited);
>  }
> @@ -3759,7 +3868,7 @@ vect_bb_slp_scalar_cost (vec_info *vinfo,
>          the scalar cost.  */
>        if (!STMT_VINFO_LIVE_P (stmt_info))
>         {
> -         FOR_EACH_SSA_DEF_OPERAND (def_p, orig_stmt, op_iter, SSA_OP_DEF)
> +         FOR_EACH_PHI_OR_STMT_DEF (def_p, orig_stmt, op_iter, SSA_OP_DEF)
>             {
>               imm_use_iterator use_iter;
>               gimple *use_stmt;
> @@ -3803,7 +3912,7 @@ vect_bb_slp_scalar_cost (vec_info *vinfo,
>    auto_vec<bool, 20> subtree_life;
>    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
>      {
> -      if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
> +      if (child && SLP_TREE_DEF_TYPE (child) == vect_internal_def)
>         {
>           /* Do not directly pass LIFE to the recursive call, copy it to
>              confine changes in the callee to the current child/subtree.  */
> @@ -4272,19 +4381,18 @@ vect_slp_function (function *fun)
>    for (unsigned i = 0; i < n; i++)
>      {
>        basic_block bb = BASIC_BLOCK_FOR_FN (fun, rpo[i]);
> -
> -      /* Split when a basic block has multiple predecessors or when the
> -        edge into it exits a loop (because of implementation issues with
> -        respect to placement of CTORs for externals).  */
>        bool split = false;
> -      edge e;
> -      if (!single_pred_p (bb)
> -         || ((e = single_pred_edge (bb)),
> -             loop_exit_edge_p (e->src->loop_father, e)))
> -       split = true;
> +
>        /* Split when a BB is not dominated by the first block.  */
> +      if (!bbs.is_empty ()
> +         && !dominated_by_p (CDI_DOMINATORS, bb, bbs[0]))
> +       split = true;
> +      /* Split when the loop determined by the first block
> +        is exited.  This is because we eventually insert
> +        invariants at region begin.  */
>        else if (!bbs.is_empty ()
> -              && !dominated_by_p (CDI_DOMINATORS, bb, bbs[0]))
> +              && bbs[0]->loop_father != bb->loop_father
> +              && !flow_loop_nested_p (bbs[0]->loop_father, bb->loop_father))
>         split = true;
>
>        if (split && !bbs.is_empty ())
> @@ -5087,24 +5195,22 @@ vectorizable_slp_permutation (vec_info *vinfo, gimple_stmt_iterator *gsi,
>    return true;
>  }
>
> -/* Vectorize SLP instance tree in postorder.  */
> +/* Vectorize SLP NODE.  */
>
>  static void
> -vect_schedule_slp_instance (vec_info *vinfo,
> -                           slp_tree node, slp_instance instance,
> -                           hash_set<slp_tree> &visited)
> +vect_schedule_slp_node (vec_info *vinfo,
> +                       slp_tree node, slp_instance instance)
>  {
>    gimple_stmt_iterator si;
>    int i;
>    slp_tree child;
>
> -  /* See if we have already vectorized the node in the graph of the
> -     SLP instance.  */
> -  if ((SLP_TREE_DEF_TYPE (node) == vect_internal_def
> -       && SLP_TREE_VEC_STMTS (node).exists ())
> -      || SLP_TREE_VEC_DEFS (node).exists ())
> +  /* For existing vectors there's nothing to do.  */
> +  if (SLP_TREE_VEC_DEFS (node).exists ())
>      return;
>
> +  gcc_assert (SLP_TREE_VEC_STMTS (node).is_empty ());
> +
>    /* Vectorize externals and constants.  */
>    if (SLP_TREE_DEF_TYPE (node) == vect_constant_def
>        || SLP_TREE_DEF_TYPE (node) == vect_external_def)
> @@ -5119,17 +5225,11 @@ vect_schedule_slp_instance (vec_info *vinfo,
>        return;
>      }
>
> -  /* ???  If we'd have a way to mark backedges that would be cheaper.  */
> -  if (visited.add (node))
> -    return;
> -
> -  FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> -    vect_schedule_slp_instance (vinfo, child, instance, visited);
> +  stmt_vec_info stmt_info = SLP_TREE_REPRESENTATIVE (node);
>
>    gcc_assert (SLP_TREE_NUMBER_OF_VEC_STMTS (node) != 0);
>    SLP_TREE_VEC_STMTS (node).create (SLP_TREE_NUMBER_OF_VEC_STMTS (node));
>
> -  stmt_vec_info stmt_info = SLP_TREE_REPRESENTATIVE (node);
>    if (dump_enabled_p ())
>      dump_printf_loc (MSG_NOTE, vect_location,
>                      "------>vectorizing SLP node starting from: %G",
> @@ -5148,13 +5248,12 @@ vect_schedule_slp_instance (vec_info *vinfo,
>         last_stmt_info = vect_find_last_scalar_stmt_in_slp (node);
>        si = gsi_for_stmt (last_stmt_info->stmt);
>      }
> -  else if ((STMT_VINFO_TYPE (SLP_TREE_REPRESENTATIVE (node))
> -           == cycle_phi_info_type)
> -          || (STMT_VINFO_TYPE (SLP_TREE_REPRESENTATIVE (node))
> -              == induc_vec_info_type))
> +  else if ((STMT_VINFO_TYPE (stmt_info) == cycle_phi_info_type
> +           || STMT_VINFO_TYPE (stmt_info) == induc_vec_info_type
> +           || STMT_VINFO_TYPE (stmt_info) == phi_info_type)
> +          && SLP_TREE_CODE (node) != VEC_PERM_EXPR)
>      {
> -      /* For reduction and induction PHIs we do not use the
> -        insertion iterator.  */
> +      /* For PHI node vectorization we do not use the insertion iterator.  */
>        si = gsi_none ();
>      }
>    else
> @@ -5277,7 +5376,7 @@ vect_remove_slp_scalar_calls (vec_info *vinfo,
>    tree lhs;
>    stmt_vec_info stmt_info;
>
> -  if (SLP_TREE_DEF_TYPE (node) != vect_internal_def)
> +  if (!node || SLP_TREE_DEF_TYPE (node) != vect_internal_def)
>      return;
>
>    if (visited.add (node))
> @@ -5359,6 +5458,142 @@ vectorize_slp_instance_root_stmt (slp_tree node, slp_instance instance)
>      gsi_replace (&rgsi, rstmt, true);
>  }
>
> +struct slp_scc_info
> +{
> +  bool on_stack;
> +  int dfs;
> +  int lowlink;
> +};
> +
> +/* Schedule the SLP INSTANCE doing a DFS walk and collecting SCCs.  */
> +
> +static void
> +vect_schedule_scc (vec_info *vinfo, slp_tree node, slp_instance instance,
> +                  hash_map<slp_tree, slp_scc_info> &scc_info,
> +                  int &maxdfs, vec<slp_tree> &stack)
> +{
> +  bool existed_p;
> +  slp_scc_info *info = &scc_info.get_or_insert (node, &existed_p);
> +  gcc_assert (!existed_p);
> +  info->dfs = maxdfs;
> +  info->lowlink = maxdfs;
> +  info->on_stack = true;
> +  maxdfs++;
> +  stack.safe_push (node);
> +  unsigned i;
> +  slp_tree child;
> +
> +  /* ???  We're keeping SLP_TREE_CHILDREN of externalized nodes.  */
> +  if (SLP_TREE_DEF_TYPE (node) == vect_internal_def)
> +    FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
> +      {
> +       if (!child)
> +         continue;
> +       slp_scc_info *child_info = scc_info.get (child);
> +       if (!child_info)
> +         {
> +           vect_schedule_scc (vinfo, child, instance, scc_info, maxdfs, stack);
> +           /* Recursion might have re-allocated the node.  */
> +           info = scc_info.get (node);
> +           child_info = scc_info.get (child);
> +           info->lowlink = MIN (info->lowlink, child_info->lowlink);
> +         }
> +       else if (child_info->on_stack)
> +         info->lowlink = MIN (info->lowlink, child_info->dfs);
> +      }
> +  if (info->lowlink != info->dfs)
> +    return;
> +
> +  /* Singleton.  */
> +  if (stack.last () == node)
> +    {
> +      stack.pop ();
> +      info->on_stack = false;
> +      vect_schedule_slp_node (vinfo, node, instance);
> +      return;
> +    }
> +  /* SCC.  */
> +  int last_idx = stack.length () - 1;
> +  while (stack[last_idx] != node)
> +    last_idx--;
> +  /* We can break the cycle at PHIs who have at least one child
> +     code generated.  Then we could re-start the DFS walk until
> +     all nodes in the SCC are covered (we might have new entries
> +     for only back-reachable nodes).  But it's simpler to just
> +     iterate and schedule those that are ready.  */
> +  auto_vec<slp_tree, 4> phis_to_fixup;
> +  unsigned todo = stack.length () - last_idx;
> +  do
> +    {
> +      for (int idx = stack.length () - 1; idx >= last_idx; --idx)
> +       {
> +         slp_tree entry = stack[idx];
> +         if (!entry)
> +           continue;
> +         bool phi = (SLP_TREE_CODE (entry) != VEC_PERM_EXPR
> +                     && is_a <gphi *> (SLP_TREE_REPRESENTATIVE (entry)->stmt));
> +         bool ready = !phi;
> +         FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (entry), i, child)
> +           if (!child)
> +             {
> +               gcc_assert (phi);
> +               ready = true;
> +               break;
> +             }
> +           else if (scc_info.get (child)->on_stack)
> +             {
> +               if (!phi)
> +                 {
> +                   ready = false;
> +                   break;
> +                 }
> +             }
> +           else
> +             {
> +               if (phi)
> +                 {
> +                   ready = true;
> +                   break;
> +                 }
> +             }
> +         if (ready)
> +           {
> +             vect_schedule_slp_node (vinfo, entry, instance);
> +             scc_info.get (entry)->on_stack = false;
> +             stack[idx] = NULL;
> +             todo--;
> +             if (phi)
> +               phis_to_fixup.safe_push (entry);
> +           }
> +       }
> +    }
> +  while (todo != 0);
> +
> +  /* Now fixup the backedge def of the vectorized PHIs in this SCC.  */
> +  slp_tree phi_node;
> +  FOR_EACH_VEC_ELT (phis_to_fixup, i, phi_node)
> +    {
> +      gphi *phi = as_a <gphi *> (SLP_TREE_REPRESENTATIVE (phi_node)->stmt);
> +      edge_iterator ei;
> +      edge e;
> +      FOR_EACH_EDGE (e, ei, gimple_bb (phi)->preds)
> +       {
> +         unsigned dest_idx = e->dest_idx;
> +         child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
> +         if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
> +           continue;
> +         /* Simply fill all args.  */
> +         for (unsigned i = 0; i < SLP_TREE_VEC_STMTS (phi_node).length (); ++i)
> +           add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
> +                        vect_get_slp_vect_def (child, i),
> +                        e, gimple_phi_arg_location (phi, dest_idx));
> +       }
> +    }
> +
> +  /* Pop the SCC.  */
> +  stack.truncate (last_idx);
> +}
> +
>  /* Generate vector code for SLP_INSTANCES in the loop/basic block.  */
>
>  void
> @@ -5367,7 +5602,8 @@ vect_schedule_slp (vec_info *vinfo, vec<slp_instance> slp_instances)
>    slp_instance instance;
>    unsigned int i;
>
> -  hash_set<slp_tree> visited;
> +  hash_map<slp_tree, slp_scc_info> scc_info;
> +  int maxdfs = 0;
>    FOR_EACH_VEC_ELT (slp_instances, i, instance)
>      {
>        slp_tree node = SLP_INSTANCE_TREE (instance);
> @@ -5381,8 +5617,11 @@ vect_schedule_slp (vec_info *vinfo, vec<slp_instance> slp_instances)
>           vect_print_slp_graph (MSG_NOTE, vect_location,
>                                 SLP_INSTANCE_TREE (instance));
>         }
> -      /* Schedule the tree of INSTANCE.  */
> -      vect_schedule_slp_instance (vinfo, node, instance, visited);
> +      /* Schedule the tree of INSTANCE, scheduling SCCs in a way to
> +        have a PHI be the node breaking the cycle.  */
> +      auto_vec<slp_tree> stack;
> +      if (!scc_info.get (node))
> +       vect_schedule_scc (vinfo, node, instance, scc_info, maxdfs, stack);
>
>        if (SLP_INSTANCE_ROOT_STMT (instance))
>         vectorize_slp_instance_root_stmt (node, instance);
> @@ -5398,25 +5637,6 @@ vect_schedule_slp (vec_info *vinfo, vec<slp_instance> slp_instances)
>        stmt_vec_info store_info;
>        unsigned int j;
>
> -      /* For reductions set the latch values of the vectorized PHIs.  */
> -      if (instance->reduc_phis
> -         && STMT_VINFO_REDUC_TYPE (SLP_TREE_REPRESENTATIVE
> -                       (instance->reduc_phis)) != FOLD_LEFT_REDUCTION
> -         && STMT_VINFO_REDUC_TYPE (SLP_TREE_REPRESENTATIVE
> -                       (instance->reduc_phis)) != EXTRACT_LAST_REDUCTION)
> -       {
> -         slp_tree slp_node = root;
> -         slp_tree phi_node = instance->reduc_phis;
> -         gphi *phi = as_a <gphi *> (SLP_TREE_SCALAR_STMTS (phi_node)[0]->stmt);
> -         edge e = loop_latch_edge (gimple_bb (phi)->loop_father);
> -         gcc_assert (SLP_TREE_VEC_STMTS (phi_node).length ()
> -                     == SLP_TREE_VEC_STMTS (slp_node).length ());
> -         for (unsigned j = 0; j < SLP_TREE_VEC_STMTS (phi_node).length (); ++j)
> -           add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[j]),
> -                        vect_get_slp_vect_def (slp_node, j),
> -                        e, gimple_phi_arg_location (phi, e->dest_idx));
> -       }
> -
>        /* Remove scalar call stmts.  Do not do this for basic-block
>          vectorization as not all uses may be vectorized.
>          ???  Why should this be necessary?  DCE should be able to
> diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
> index 3575f25241f..7f0763f15c4 100644
> --- a/gcc/tree-vect-stmts.c
> +++ b/gcc/tree-vect-stmts.c
> @@ -10745,7 +10745,8 @@ vect_analyze_stmt (vec_info *vinfo,
>               || vectorizable_condition (vinfo, stmt_info,
>                                          NULL, NULL, node, cost_vec)
>               || vectorizable_comparison (vinfo, stmt_info, NULL, NULL, node,
> -                                         cost_vec));
> +                                         cost_vec)
> +             || vectorizable_phi (vinfo, stmt_info, NULL, node));
>      }
>
>    if (!ok)
> @@ -10885,6 +10886,11 @@ vect_transform_stmt (vec_info *vinfo,
>        gcc_assert (done);
>        break;
>
> +    case phi_info_type:
> +      done = vectorizable_phi (vinfo, stmt_info, &vec_stmt, slp_node);
> +      gcc_assert (done);
> +      break;
> +
>      default:
>        if (!STMT_VINFO_LIVE_P (stmt_info))
>         {
> diff --git a/gcc/tree-vectorizer.c b/gcc/tree-vectorizer.c
> index 0e08652ed10..b63dda31a08 100644
> --- a/gcc/tree-vectorizer.c
> +++ b/gcc/tree-vectorizer.c
> @@ -684,7 +684,8 @@ vec_info::new_stmt_vec_info (gimple *stmt)
>    STMT_VINFO_SLP_VECT_ONLY (res) = false;
>    STMT_VINFO_VEC_STMTS (res) = vNULL;
>
> -  if (gimple_code (stmt) == GIMPLE_PHI
> +  if (is_a <loop_vec_info> (this)
> +      && gimple_code (stmt) == GIMPLE_PHI
>        && is_loop_header_bb_p (gimple_bb (stmt)))
>      STMT_VINFO_DEF_TYPE (res) = vect_unknown_def_type;
>    else
> diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
> index 9c55383a3ee..13a02cd0d0c 100644
> --- a/gcc/tree-vectorizer.h
> +++ b/gcc/tree-vectorizer.h
> @@ -881,6 +881,7 @@ enum stmt_vec_info_type {
>    type_conversion_vec_info_type,
>    cycle_phi_info_type,
>    lc_phi_info_type,
> +  phi_info_type,
>    loop_exit_ctrl_vec_info_type
>  };
>
> @@ -1939,6 +1940,7 @@ extern bool vect_transform_cycle_phi (loop_vec_info, stmt_vec_info,
>                                       slp_tree, slp_instance);
>  extern bool vectorizable_lc_phi (loop_vec_info, stmt_vec_info,
>                                  gimple **, slp_tree);
> +extern bool vectorizable_phi (vec_info *, stmt_vec_info, gimple **, slp_tree);
>  extern bool vect_worthwhile_without_simd_p (vec_info *, tree_code);
>  extern int vect_get_known_peeling_cost (loop_vec_info, int, int *,
>                                         stmt_vector_for_cost *,
> --
> 2.26.2


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