[gcc r13-2738] vect: Fix SLP layout handling of masked loads [PR106794]

[Richard Sandiford <rsandifo@gcc.gnu.org>]

https://gcc.gnu.org/g:1005c89431cc78a68762643e1bc7249c3959927e

commit r13-2738-g1005c89431cc78a68762643e1bc7249c3959927e
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Sep 20 15:27:47 2022 +0100

    vect: Fix SLP layout handling of masked loads [PR106794]
    
    PR106794 shows that I'd forgotten about masked loads when
    doing the SLP layout changes.  These loads can't currently
    be permuted independently of their mask input, so during
    construction they never get a load permutation.
    
    (If we did support permuting masked loads in future, the mask
    would need to be in the right order for the load, rather than in
    the order implied by the result of the permutation.  Since masked
    loads can't be partly or fully scalarised in the way that normal
    permuted loads can be, there's probably no benefit to fusing the
    permutation and the load.  Permutation after the fact is probably
    good enough.)
    
    gcc/
            PR tree-optimization/106794
            PR tree-optimization/106914
            * tree-vect-slp.cc (vect_optimize_slp_pass::internal_node_cost):
            Only consider loads that already have a permutation.
            (vect_optimize_slp_pass::start_choosing_layouts): Assert that
            loads with permutations are leaf nodes.  Prevent any kind of grouped
            access from changing layout if it doesn't have a load permutation.
    
    gcc/testsuite/
            * gcc.dg/vect/pr106914.c: New test.
            * g++.dg/vect/pr106794.cc: Likewise.

Diff:
---
 gcc/testsuite/g++.dg/vect/pr106794.cc | 40 +++++++++++++++++++++++++++++++++++
 gcc/testsuite/gcc.dg/vect/pr106914.c  | 15 +++++++++++++
 gcc/tree-vect-slp.cc                  | 30 +++++++++++++++++++-------
 3 files changed, 77 insertions(+), 8 deletions(-)

diff --git a/gcc/testsuite/g++.dg/vect/pr106794.cc b/gcc/testsuite/g++.dg/vect/pr106794.cc
new file mode 100644
index 00000000000..f056563c4e1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/vect/pr106794.cc
@@ -0,0 +1,40 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-Ofast" } */
+/* { dg-additional-options "-march=bdver2" { target x86_64-*-* i?86-*-* } } */
+
+template <class T> struct Vector3 {
+  Vector3();
+  Vector3(T, T, T);
+  T length() const;
+  T x, y, z;
+};
+template <class T>
+Vector3<T>::Vector3(T _x, T _y, T _z) : x(_x), y(_y), z(_z) {}
+Vector3<float> cross(Vector3<float> a, Vector3<float> b) {
+  return Vector3<float>(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z,
+                        a.x * b.y - a.y * b.x);
+}
+template <class T> T Vector3<T>::length() const { return z; }
+int generateNormals_i;
+float generateNormals_p2_0, generateNormals_p0_0;
+struct SphereMesh {
+  void generateNormals();
+  float vertices;
+};
+void SphereMesh::generateNormals() {
+  Vector3<float> *faceNormals = new Vector3<float>;
+  for (int j; j; j++) {
+    float *p0 = &vertices + 3, *p1 = &vertices + j * 3, *p2 = &vertices + 3,
+          *p3 = &vertices + generateNormals_i + j * 3;
+    Vector3<float> v0(p1[0] - generateNormals_p0_0, p1[1] - 1, p1[2] - 2),
+        v1(0, 1, 2);
+    if (v0.length())
+      v1 = Vector3<float>(p3[0] - generateNormals_p2_0, p3[1] - p2[1],
+                          p3[2] - p2[2]);
+    else
+      v1 = Vector3<float>(generateNormals_p0_0 - p3[0], p0[1] - p3[1],
+                          p0[2] - p3[2]);
+    Vector3<float> faceNormal = cross(v0, v1);
+    faceNormals[j] = faceNormal;
+  }
+}
diff --git a/gcc/testsuite/gcc.dg/vect/pr106914.c b/gcc/testsuite/gcc.dg/vect/pr106914.c
new file mode 100644
index 00000000000..9d9b3e30081
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr106914.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fprofile-generate" } */
+/* { dg-additional-options "-mavx512vl" { target x86_64-*-* i?86-*-* } } */
+
+int *mask_slp_int64_t_8_2_x, *mask_slp_int64_t_8_2_y, *mask_slp_int64_t_8_2_z;
+
+void
+__attribute__mask_slp_int64_t_8_2() {
+  for (int i; i; i += 8) {
+    mask_slp_int64_t_8_2_x[i + 6] =
+        mask_slp_int64_t_8_2_y[i + 6] ? mask_slp_int64_t_8_2_z[i] : 1;
+    mask_slp_int64_t_8_2_x[i + 7] =
+        mask_slp_int64_t_8_2_y[i + 7] ? mask_slp_int64_t_8_2_z[i + 7] : 2;
+  }
+}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index ca3422c2a1e..229f2663ebc 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -4494,7 +4494,8 @@ vect_optimize_slp_pass::internal_node_cost (slp_tree node, int in_layout_i,
   stmt_vec_info rep = SLP_TREE_REPRESENTATIVE (node);
   if (rep
       && STMT_VINFO_DATA_REF (rep)
-      && DR_IS_READ (STMT_VINFO_DATA_REF (rep)))
+      && DR_IS_READ (STMT_VINFO_DATA_REF (rep))
+      && SLP_TREE_LOAD_PERMUTATION (node).exists ())
     {
       auto_load_permutation_t tmp_perm;
       tmp_perm.safe_splice (SLP_TREE_LOAD_PERMUTATION (node));
@@ -4569,8 +4570,12 @@ vect_optimize_slp_pass::start_choosing_layouts ()
       if (SLP_TREE_LOAD_PERMUTATION (node).exists ())
 	{
 	  /* If splitting out a SLP_TREE_LANE_PERMUTATION can make the node
-	     unpermuted, record a layout that reverses this permutation.  */
-	  gcc_assert (partition.layout == 0);
+	     unpermuted, record a layout that reverses this permutation.
+
+	     We would need more work to cope with loads that are internally
+	     permuted and also have inputs (such as masks for
+	     IFN_MASK_LOADs).  */
+	  gcc_assert (partition.layout == 0 && !m_slpg->vertices[node_i].succ);
 	  if (!STMT_VINFO_GROUPED_ACCESS (dr_stmt))
 	    continue;
 	  dr_stmt = DR_GROUP_FIRST_ELEMENT (dr_stmt);
@@ -4684,12 +4689,21 @@ vect_optimize_slp_pass::start_choosing_layouts ()
 	  vertex.weight = vect_slp_node_weight (node);
 
 	  /* We do not handle stores with a permutation, so all
-	     incoming permutations must have been materialized.  */
+	     incoming permutations must have been materialized.
+
+	     We also don't handle masked grouped loads, which lack a
+	     permutation vector.  In this case the memory locations
+	     form an implicit second input to the loads, on top of the
+	     explicit mask input, and the memory input's layout cannot
+	     be changed.
+
+	     On the other hand, we do support permuting gather loads and
+	     masked gather loads, where each scalar load is independent
+	     of the others.  This can be useful if the address/index input
+	     benefits from permutation.  */
 	  if (STMT_VINFO_DATA_REF (rep)
-	      && DR_IS_WRITE (STMT_VINFO_DATA_REF (rep)))
-	    /* ???  We're forcing materialization in place
-	       of the child here, we'd need special handling
-	       in materialization to leave layout -1 here.  */
+	      && STMT_VINFO_GROUPED_ACCESS (rep)
+	      && !SLP_TREE_LOAD_PERMUTATION (node).exists ())
 	    partition.layout = 0;
 
 	  /* We cannot change the layout of an operation that is