[Bug tree-optimization/99776] missed optimization for dead code elimination at -O3 (vs. -O1)

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99776

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
diff --git a/gcc/match.pd b/gcc/match.pd
index 036f92fa959..61c93b5edd1 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

works to fix the testcase.  The issue is that we vectorize pointer data
as unsigned long and the type mismatch prevents the folding.  With the above
FRE4 produces

  <bb 2> [local count: 118111601]:
  _10 = (long unsigned int) &a[1];
  vect_cst__4 = {_10, _10};
  MEM <vector(2) long unsigned int> [(int * *)&c] = vect_cst__4;
  b = 2;
  return 0;

as desired.  Queued for GCC 12.