[PATCH 1/2] Seperate -funroll-loops for GIMPLE unroller and RTL unroller

[Segher Boessenkool]

On Mon, May 25, 2020 at 02:14:02PM +0200, Richard Biener wrote:
> On Mon, May 25, 2020 at 1:10 PM guojiufu <guojiufu@linux.ibm.com> wrote:
> Since a new flag is not needed to fix the regression please avoid
> adding -fcomplete-unroll-loops.
> 
> For -frtl-unroll-loops you should be able to use

Erm.  That *is* a new command-line option (the internal flags I do not
care about so much: new implementation details are *good*).  And a new
name that is a mistake in my opinion, for many reasons (users do not
know and should not have to care about "rtl"; the name is not
descriptive; it is useless churn, it is not the same name as we have
had for decades now; it is adding a new option for a future where we
will do most unrolling at gimple level, a future we do not know will
ever exist, and we do not know what that will look like anyway; it is
an extra level of indirection (in the name)).

We should not have an -frtl-unroll-loops if we do not have a
-ftree-unroll-loops (or whatever).

Unrolling early is not a good idea in general (the problems with the
very trivial complete unrolling case just underline that).  But we
*should* know which code we expect to unroll later, for better costing.
Adding names like "rtl-unroll-loops" only stands in the way of getting
a better design here.


Segher