Re: [PATCH] ivopts costs debug

[Segher Boessenkool <segher@kernel.crashing.org>]

On Wed, Aug 19, 2015 at 10:45:42AM +0800, Bin.Cheng wrote:
> I ran into back-end address cost issue before and this should be
> useful in such cases.  Though there are a lot of dumps, it would be
> better to classify it into existing dump option (TDF_DETAILS?) and
> discard the use of macro.

But TDF_DETAILS is enabled pretty much always, and this costs dump
isn't to debug ivopts _itself_.  I got the idea from lower-subreg.c,
which also uses debug macros like this (and is another place where
bad costs tend to show up, btw).

> Also the address cost will be tuned/dumped
> later, we should differentiate between them by emphasizing this part
> of dump is the original cost from back-end.

Yeah I should probably print some header, also say e.g. what machine
mode some table is for.

> > It also shows that the LAST_VIRTUAL_REGISTER trickery ivopts does
> > does not work (legitimize_address can create new registers, so now
> > a) we have new registers anyway, and b) we use some for multiple
> > purposes.  Oops).
> Yes, that makes seq dump a little weird.

It can even make the result wrong -- e.g. (plus (reg 155) (reg 155))
could  well be costed differently than (plus (reg 155) (reg 159)).


Segher