[PATCH 3/4] match.pd: Teach forwprop to handle VLA VEC_PERM_EXPRs with VLS CONSTRUCTORs as arguments

["Andre Vieira (lists)" <andre.simoesdiasvieira@arm.com>]

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Hi,

This patch is part of the WIP patch that follows in this series. It's 
goal is to teach forwprop to handle VLA VEC_PERM_EXPRs with VLS 
CONSTRUCTORs as arguments as preparation for the 'VLA constructor' hook 
approach.

Kind Regards,
Andre

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diff --git a/gcc/match.pd b/gcc/match.pd
index 9736393061aac61d4d53aaad6cf6b2c97a7d4679..3c3c0c6a88b35a6e42c506f6c4603680fe6e4318 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -7852,14 +7852,24 @@ and,
     if (!tree_to_vec_perm_builder (&builder, op2))
       return NULL_TREE;
 
+    /* FIXME: disable folding of a VEC_PERM_EXPR with a VLA mask and VLS
+       CONSTRUCTORS, since that would yield a VLA CONSTRUCTOR which we
+       currently do not support.  */
+    if (!TYPE_VECTOR_SUBPARTS (type).is_constant ()
+	&& (TYPE_VECTOR_SUBPARTS (TREE_TYPE (op0)).is_constant ()
+	    || TYPE_VECTOR_SUBPARTS (TREE_TYPE (op1)).is_constant ()))
+      return NULL_TREE;
+
     /* Create a vec_perm_indices for the integer vector.  */
     poly_uint64 nelts = TYPE_VECTOR_SUBPARTS (type);
     bool single_arg = (op0 == op1);
     vec_perm_indices sel (builder, single_arg ? 1 : 2, nelts);
   }
-  (if (sel.series_p (0, 1, 0, 1))
+  (if (sel.series_p (0, 1, 0, 1)
+       && useless_type_conversion_p (type, TREE_TYPE (op0)))
    { op0; }
-   (if (sel.series_p (0, 1, nelts, 1))
+   (if (sel.series_p (0, 1, nelts, 1)
+	&& useless_type_conversion_p (type, TREE_TYPE (op1)))
     { op1; }
     (with
      {
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index fdc4bc8909d2763876550e53277ff2b3dcca796a..cda91c21c476ea8611e12c593bfa64e1d71dd29e 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -2661,7 +2661,7 @@ simplify_permutation (gimple_stmt_iterator *gsi)
 
       /* Shuffle of a constructor.  */
       bool ret = false;
-      tree res_type = TREE_TYPE (arg0);
+      tree res_type = TREE_TYPE (gimple_get_lhs (stmt));
       tree opt = fold_ternary (VEC_PERM_EXPR, res_type, arg0, arg1, op2);
       if (!opt
 	  || (TREE_CODE (opt) != CONSTRUCTOR && TREE_CODE (opt) != VECTOR_CST))