tree-optimization/99776 - relax condition on vector ctor element extract

This relaxes the condition for the match.pd pattern doing vector ctor
element extracts to not require type identity but only size equality.
Since we vectorize pointer data as unsigned integer data such mismatches
have to be tolerated to optimize scalar code uses of vector results.

2021-03-26  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/99776
	* match.pd (bit_field_ref (ctor)): Relax element extract
	type compatibility checks.

	* gcc.dg/tree-ssa/ssa-fre-91.c: New testcase.

diff --git a/gcc/match.pd b/gcc/match.pd
index 66788ba..bb1d623 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -6168,9 +6168,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 (simplify
  (BIT_FIELD_REF CONSTRUCTOR@0 @1 @2)
  (if (VECTOR_TYPE_P (TREE_TYPE (@0))
-      && (types_match (type, TREE_TYPE (TREE_TYPE (@0)))
+      && tree_fits_uhwi_p (TYPE_SIZE (type))
+      && ((tree_to_uhwi (TYPE_SIZE (type))
+          == tree_to_uhwi (TYPE_SIZE (TREE_TYPE (TREE_TYPE (@0)))))
           || (VECTOR_TYPE_P (type)
-             && types_match (TREE_TYPE (type), TREE_TYPE (TREE_TYPE (@0))))))
+             && (tree_to_uhwi (TYPE_SIZE (TREE_TYPE (type)))
+                 == tree_to_uhwi (TYPE_SIZE (TREE_TYPE (TREE_TYPE (@0))))))))
   (with
    {
      tree ctor = (TREE_CODE (@0) == SSA_NAME
@@ -6226,10 +6229,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
                  if (!CONSTANT_CLASS_P (e))
                    constant_p = false;
                }
-             res = (constant_p ? build_vector_from_ctor (type, vals)
-                    : build_constructor (type, vals));
+             tree evtype = (types_match (TREE_TYPE (type),
+                                         TREE_TYPE (TREE_TYPE (ctor)))
+                            ? type
+                            : build_vector_type (TREE_TYPE (TREE_TYPE (ctor)),
+                                                 count));
+             res = (constant_p ? build_vector_from_ctor (evtype, vals)
+                    : build_constructor (evtype, vals));
            }
-           { res; })))))
+           (view_convert { res; }))))))
       /* The bitfield references a single constructor element.  */
       (if (k.is_constant (&const_k)
           && idx + n <= (idx / const_k + 1) * const_k)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-91.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-91.c
new file mode 100644 (file)
index 0000000..4999a3b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-91.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-fre4" } */
+
+extern void foo(void);
+
+static int a[2], b, *c[2];
+
+int main() {
+  for (b = 0; b < 2; b++)
+    c[b] = &a[1];
+  if (!c[0])
+    foo();
+  return 0;
+}
+
+/* Even when vectorizing we should eliminate the call to foo.  */
+/* { dg-final { scan-tree-dump-not "foo" "fre4" } } */