On Tue, Jan 30, 2018 at 03:55:58AM -0600, Segher Boessenkool wrote:
> > But in that case, what does the copying?
>
> I don't know. Aaron will look at it, but timezones etc. :-)
>
> > That's what seems strange. I can see why we'd have two nested
> > pluses with the inner plus being pointer-equal to internal_arg_ptr.
> > And I can see why we'd have a single canonical plus (which IMO would
> > be better, but I agree it's not stage 4 material). It's having the two
> > nested pluses without maintaining pointer equality that seems strange.
>
> The inner plus is *not* pointer-equal, that is the problem. Something
> did copy_rtx (or such) on it, many things do. We can tell you what
> exactly later today.
Most likely unshare_all_rtl, which does:
for (tree decl = DECL_ARGUMENTS (cfun->decl); decl; decl = DECL_CHAIN (decl))
{
if (DECL_RTL_SET_P (decl))
SET_DECL_RTL (decl, copy_rtx_if_shared (DECL_RTL (decl)));
DECL_INCOMING_RTL (decl) = copy_rtx_if_shared (DECL_INCOMING_RTL (decl));
}
Anyway, my preference would be to change that gen_rtx_PLUS into
stack_parm = crtl->args.internal_arg_pointer;
if (!CONST_INT_P (offset_rtx))
stack_parm = gen_rtx_PLUS (Pmode, stack_parm, offset_rtx);
else if (offset_rtx != const0_rtx)
stack_parm = plus_constant (Pmode, stack_parm, INTVAL (offset_rtx));
stack_parm = gen_rtx_MEM (data->promoted_mode, stack_parm);
and deal specially with GET_CODE (crtl->args.internal_arg_pointer)
in var-tracking.c.
rs6000/powerpcspe with -fsplit-stack are the only cases where
crtl->args.internal_arg_pointer is not a REG, so just running libgo
testsuite on powerpc{,64,64le} should cover it all.
Jakub
