[Bug tree-optimization/80293] [6/7 Regression] unnecessary code at -O2 (-O1 is fine)

["jamborm at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80293

--- Comment #5 from Martin Jambor <jamborm at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #4)
> That said, the array cases we've seen are somewhat disturbing...  

Cases?  Can you point me to the other ones, please?  What type do they
have?

> maybe we can disable total scalarization for those?

The support for total scalarization of arrays was added by Alan
Lawrence as a part of constant pool SRA and I suppose that for a good
reason (the added testcases have them at least).

However, thinking about this particular testcase a bit more, I think
the most reasonable thing to do is to disable total scalarization of
char (or generally byte-sized-element) arrays.  Those are likely just
some anonymous storage anyway:

diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 02453d3ed9a..cbe9e862a2f 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -981,7 +981,7 @@ scalarizable_type_p (tree type)
       if (TYPE_DOMAIN (type) == NULL_TREE
          || !tree_fits_shwi_p (TYPE_SIZE (type))
          || !tree_fits_shwi_p (TYPE_SIZE (TREE_TYPE (type)))
-         || (tree_to_shwi (TYPE_SIZE (TREE_TYPE (type))) <= 0)
+         || (tree_to_shwi (TYPE_SIZE (TREE_TYPE (type))) <= BITS_PER_UNIT)
          || !tree_fits_shwi_p (TYPE_MIN_VALUE (TYPE_DOMAIN (type))))
        return false;
       if (tree_to_shwi (TYPE_SIZE (type)) == 0