Re: [PATCH] PR80101: Fix ICE in store_data_bypass_p

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

On Fri, Apr 07, 2017 at 10:39:03AM +0200, Eric Botcazou wrote:
> > Or we could just change "blockage" and wait for the next bug report.
> 
> That's my suggestion, yes.
> 
> > Alternatively, we can arrange for the bypass functions to not ICE.  We
> > can do that specific to these rs6000 pipeline descriptions, by having
> > our own version of store_data_bypass_p; or we can make that function
> > work for all insns (its definition works fine for insn pairs where
> > not both the producer and consumer are SETs).  That's what Kelvin's
> > patch does.  What is the value in ICEing here?
> 
> Telling the back-end writer that something may be wrong somewhere instead of 
> silently accepting nonsense?

Why is it nonsense?  The predicate gives the answer to the question
"given these insns A and B, does A feed data that B stores in memory".
That is a perfectly valid question to ask of any two insns.

> How long have all the assertions been there?

There are workarounds to this problem as well: mips_store_data_bypass_p,
added in 2006.  mep_store_data_bypass_p, added in 2009 (the port has
been removed since then, of course).


Segher