Re: [PATCH 2/7] PowerPC tests: Add PLI/PADDI tests.

[Michael Meissner <meissner@linux.ibm.com>]

On Mon, Jun 29, 2020 at 01:42:56PM -0500, Segher Boessenkool wrote:
> Hi!
> 
> On Mon, Jun 29, 2020 at 02:23:22PM -0400, Michael Meissner wrote:
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/powerpc/prefix-di-constant.c
> > @@ -0,0 +1,13 @@
> > +/* { dg-do compile } */
> > +/* { dg-require-effective-target powerpc_prefixed_addr } */
> > +/* { dg-require-effective-target lp64 } */
> 
> Please always say (_in the test_) why something is required, if it isn't
> obvious.
> 
> > +/* { dg-options "-O2 -mdejagnu-cpu=power10" } */
> > +
> > +/* Test that PLI (PADDI) is generated to load a large constant.  */
> > +unsigned long long
> > +large (void)
> > +{
> > +  return 0x12345678ULL;
> > +}
> > +
> > +/* { dg-final { scan-assembler {\mpli\M} } } */
> 
> I have no idea why 64-bit mode (or 64-bit addressing) is needed here.
> *Is* it needed?

Yes it is needed.  Otherwise two separate load immediates would be needed to
load each part of the DI constant that is held in 2 registers.

> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/powerpc/prefix-ds-dq.c
> > @@ -0,0 +1,161 @@
> > +/* { dg-do compile } */
> > +/* { dg-require-effective-target powerpc_prefixed_addr } */
> > +/* { dg-require-effective-target lp64 } */
> > +/* { dg-options "-O2 -mdejagnu-cpu=power10" } */
> 
> > +  unsigned int si;			/* offset 49 bytes.  */
> 
> > +int
> > +load_si (struct packed_struct *p)
> > +{
> > +  return p->si;				/* PLWA 3,49(3).  */
> > +}
> 
> Here it is because this would be just lwz on 32-bit.
> 
> But that is the only difference, so you could just make that single test
> conditional, not the whole file.
> 
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/powerpc/prefix-no-update.c
> > @@ -0,0 +1,51 @@
> > +/* { dg-do compile } */
> > +/* { dg-require-effective-target powerpc_prefixed_addr } */
> > +/* { dg-require-effective-target lp64 } */
> > +/* { dg-options "-O2 -mdejagnu-cpu=power10" } */
> 
> For this testcase, I have no idea at all why you want lp64?

Becuase to show the bug you need a stack frame larger than 64K.

-- 
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