Re: [PATCH], Add power9 support to GCC, patch #4

[Michael Meissner <meissner at linux dot vnet dot ibm dot com>]

On Mon, Nov 09, 2015 at 10:29:10AM -0600, Segher Boessenkool wrote:
> On Sun, Nov 08, 2015 at 07:39:14PM -0500, Michael Meissner wrote:
> > +;; Pretend we have a memory form of extswsli until register allocation is done
> > +;; so that we use LWZ to load the value from memory, instead of LWA.
> 
> We generate sign_extend loads for many cases where zero_extend would be
> preferable.  We should deal with that generically, and then we can lose
> this hack.

Well it would be nice in theory.  But since we don't have that generic pass, I
need to use the combiner to generate the instruction.

> > +(define_insn_and_split "*ashdi3_extswsli_dot"
> 
> ...
> 
> > +  if (REGNO (cr) == CR0_REGNO)
> > +    {
> > +      emit_insn (gen_ashdi3_extswsli_dot2 (dest, src2, shift, cr));
> > +      DONE;
> > +    }
> 
> s/dot2/dot/

No, it will endless recurse until there is a stack overflow if you use dot
(since it will call itself, generating the same pattern over and over again).

> > +/* { dg-final { scan-assembler     "extswsli\\. " } } */
> > +/* { dg-final { scan-assembler     "lwz "         } } */
> > +/* { dg-final { scan-assembler-not "lwa "         } } */
> 
> "lwa" is a nasty string to search for ("always").  You can write this as
> {\mlwa\M} for more sanity.
> 
> > +/* { dg-final { scan-assembler-not "sldi "        } } */
> > +/* { dg-final { scan-assembler-not "sldi\\. "     } } */
> 
> Similarly {\msldi\M} catches both.

Thanks.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.vnet.ibm.com, phone: +1 (978) 899-4797