[PATCH, V3, #6 of 10], Fix vec_extract breakage

[Michael Meissner]

On Tue, Sep 03, 2019 at 02:49:01PM -0500, Segher Boessenkool wrote:
> Hi!
> 
> On Mon, Aug 26, 2019 at 05:20:12PM -0400, Michael Meissner wrote:
> > @@ -3249,9 +3249,10 @@ (define_insn "vsx_vslo_<mode>"
> >  ;; Variable V2DI/V2DF extract
> >  (define_insn_and_split "vsx_extract_<mode>_var"
> >    [(set (match_operand:<VS_scalar> 0 "gpc_reg_operand" "=v,wa,r")
> > -	(unspec:<VS_scalar> [(match_operand:VSX_D 1 "input_operand" "v,m,m")
> > -			     (match_operand:DI 2 "gpc_reg_operand" "r,r,r")]
> > -			    UNSPEC_VSX_EXTRACT))
> > +	(unspec:<VS_scalar>
> > +	 [(match_operand:VSX_D 1 "reg_or_non_pcrel_operand" "v,ep,ep")
> > +	  (match_operand:DI 2 "gpc_reg_operand" "r,r,r")]
> > +	 UNSPEC_VSX_EXTRACT))
> >     (clobber (match_scratch:DI 3 "=r,&b,&b"))
> >     (clobber (match_scratch:V2DI 4 "=&v,X,X"))]
> >    "VECTOR_MEM_VSX_P (<MODE>mode) && TARGET_DIRECT_MOVE_64BIT"
> 
> After this patch, what happens if you have this instruction generated
> with some pcrel memory?  This pattern will no longer match.  Or can that
> not happen?  Many places call gen_vsx_extract_*.

No, the only place that calls it directly is rs6000_expand_vector_extract.
There are multiple references to gen_vsx_extract_<mode>_var because it has a
switch statement to call the appropriate generator based on the mode.  When
rs6000_expand_vector_extract is called, it is in the expand phase of RTL, and a
force_reg has been done to move the vector into a register.

What this patch does is prevent the combiner from merging the load and extract
in the one case where it is loading the value from a pc-relative address.  In
that case, the compiler will just load the vector into a register, and then do
the normal variable extract from a register.

> I wouldn't use "ep" for *non*-pcrel.  The new constraints/predicates don't
> need to do everything in a C block.  Looks good otherwise.

Any particular suggestions for the spelling?

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