Re: [PATCH, rs6000] TARGET_MADDLD should include TARGET_POWERPC64

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

Hi!

On Thu, Aug 04, 2022 at 11:17:48AM +0800, HAO CHEN GUI wrote:
> On 4/8/2022 上午 12:54, Segher Boessenkool wrote:
> > Hrm.  But the maddld insn is useful for SImode as well, in 32-bit mode,
> > it is just its name that is a bit confusing then.  Sorry for confusing
> > things :-(
> > 
> > Add a test for SImode maddld as well?
> 
>  Thanks for your comments.
> 
>  Just want to double confirm that a maddld test case with "-m32" and
> "-mpowerpc64" is needed. As far as I understand, maddld is a 64-bit
> instruction and it should be used with "-mpowerpc64" in a 32-bit register
> environment.

Nope.  The instruction is fine in pure 32 bit as well.

Almost all instructions actually work on 64 bits, but for many
(including this maddld) the low 32 bits of the result make sense on
their own, as a 32-bit operation done on the low 32 bits of the input
registers.

We have
  (define_mode_iterator GPR [SI (DI "TARGET_POWERPC64")])
so that :DI will not be used for plain -m32 compilations, but it can
(and will, and should) be used for -m32 -mpowerpc64, and :SI can be used
for -m32 in every case.

Instructions that look at the top 32 bits of a GPR need an explicit
TARGET_POWERPC64.


Segher