Re: [RFC]: Remove Mem/address type assumption in combiner

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

On Fri, May 15, 2015 at 10:40:48PM -0400, Hans-Peter Nilsson wrote:
> I confess the test-case-"guarded" addi pattern should have been
> expressed with a shift in addition to the multiplication.

But they wouldn't ever match so they might very well have bitrotted
by now :-(

> ("In
> addition to" as the canonically wrong one used to be the
> combine-matching pattern; I'm not sure I should really drop that
> just yet.)

It is harmless to leave it in.  It will rot though, eventually --
better take it out before then.  Add some gcc_unreachable, perhaps.

> Supposedly more noteworthy: this now-stricter canonicalization
> leads to a requirement to rewrite patterns that used to be:
> 
>  (parallel
>   [(set reg0 (mem (plus (mult reg1 N) reg2)))
>    (set reg3 (plus (mult reg1 N) reg2))])
> 
> into the awkwardly asymmetric:
> 
>  (parallel
>   [(set reg0 (mem (plus (mult reg1 2) reg2)))
>    (set reg3 (plus (ashift reg1 M) reg2))])
> 
> (where M = log2 N)

Yeah.  This is true of parallels in general: canonicalisation works
on each arm separately.  I'm not sure what can be done about it.


Looks like quite some work for you, I'm sorry about that,


Segher