[gcc r12-139] tree-optimization/99776 - relax condition on vector ctor element extract

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:7d6bb80931b429631f63e0fd27bee95f32eb57a9

commit r12-139-g7d6bb80931b429631f63e0fd27bee95f32eb57a9
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Mar 26 09:50:03 2021 +0100

    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:
---
 gcc/match.pd                               | 18 +++++++++++++-----
 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-91.c | 17 +++++++++++++++++
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/gcc/match.pd b/gcc/match.pd
index 66788ba6a86..bb1d6231de1 100644
--- 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
index 00000000000..4999a3b66ab
--- /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" } } */