On May 17, 2019 6:47:00 PM GMT+02:00, Jeff Law <l...@redhat.com> wrote:
>On 5/16/19 10:17 PM, Feng Xue OS wrote:
>> This patch is meant to give user a way to optimize away those empty
>loops which are impossible to be recognized by compiler, such as C++
>STL container-based loop,
>>
>> void f (std::map<int, int> &m)
>> {
>> for (auto it = m.begin (); it != m.end (); ++it);
>> }
>>
>> An option "-ffinite-loop" is added to tell compiler about finiteness
>of loops so that compiler can apply the optimization.
>>
>> Feng
>>
>> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
>> index d8bed3a..c55f2e6 100644
>> --- a/gcc/ChangeLog
>> +++ b/gcc/ChangeLog
>> @@ -1,3 +1,18 @@
>> +2019-05-16 Feng Xue <f...@os.amperecomputing.com>
>> +
>> + PR tree-optimization/89713
>> + * doc/invoke.texi (-ffinite-loop): Document new option.
>> + * common.opt (-ffinite-loop): New option.
>> + * passes.def: Replace pass_cd_dce with pass_cd_dce2.
>> + * tree-pass.h (pass_cd_dce2): New declaration.
>> + * tree-ssa-dce.c (loop_has_true_exits): New function.
>> + (find_obviously_necessary_stmts): Add
>aggressive_loop_removal
>> + parameter.
>> + (perform_tree_ssa_dce, tree_ssa_cd_dce): Likewise.
>> + (class pass_cd_dce): Add new member aggressive_loop_removal.
>> + (pass_cd_dce::pass_cd_dce: Add alr parameter.
>> + (make_pass_cd_dce2): New function.
>I'm not a big fan of this patch. I'd rather be looking at either
>improving our analysis or adding attributes to the loops to help the
>analysis bits prove termination.
And we had sth similar in the past and ended up removing it.
-funsafe-loop-optimizations IIRC.
Richard.
>Jeff
