[PATCH PR93674]Avoid introducing IV of enumeral type in case of -fstrict-enums

[Richard Biener]

On Mon, Mar 2, 2020 at 9:07 AM bin.cheng <bin.cheng@linux.alibaba.com> wrote:
>
> Hi,
> This is a simple fix for PR93674.  It adds cand carefully for enumeral type iv_use in
> case of -fstrict-enums, it also avoids computing, replacing iv_use with the candidate
> so that no IV of enumeral type is introduced with -fstrict-enums option.
>
> Testcase is also added.  Bootstrap and test on x86_64.  Any comment?

I think we should avoid enum-typed (or bool-typed) IVs in general, not just
with -fstrict-enums.  That said, the ENUMERAL_TYPE checks should be
!(INTEGER_TYPE || POINTER_TYPE_P) checks.

+  /* Check if cand can represent values of use for strict enums.  */
+  else if (TREE_CODE (ctype) == ENUMERAL_TYPE && flag_strict_enums)
+    {

if we don't have enum-typed IV candidates then the computation should
be carried out in INTEGER_TYPE and then be converted to enum type.
So why's this and the may_eliminate_iv hunks necessary?

Richard.

> Thanks,
> bin
> 2020-03-02  Bin Cheng  <bin.cheng@linux.alibaba.com>
>
>         PR tree-optimization/93674
>         * tree-ssa-loop-ivopts.c (add_iv_candidate_for_use): Add candidate
>         for enumeral type iv_use converted from other iv.
>         (get_computation_cost, may_eliminate_iv): Avoid compute, eliminate
>         iv_use with enumeral type iv_cand in case of -fstrict-enums.
>
> gcc/testsuite
> 2020-03-02  Bin Cheng  <bin.cheng@linux.alibaba.com>
>
>         PR tree-optimization/93674
>         * g++.dg/pr93674.C: New test.