[PATCH] rs6000: __builtin_darn[_raw] should be in [power9-64] (PR103624)

[Segher Boessenkool]

On Mon, Dec 13, 2021 at 02:37:43PM -0600, Bill Schmidt wrote:
> On 12/13/21 10:54 AM, Segher Boessenkool wrote:
> > On Mon, Dec 13, 2021 at 11:30:28AM -0500, David Edelsohn wrote:
> >> On Mon, Dec 13, 2021 at 10:48 AM Bill Schmidt <wschmidt@linux.ibm.com> wrote:
> >>> PR103624 observes that we get segfaults for the 64-bit darn builtins when compiled
> >>> on a 32-bit architecture.  The old built-in infrastructure requires TARGET_64BIT, and
> >>> this was missed in the new support.  Moving these two builtins from the [power9]
> >>> stanza to the [power9-64] stanza solves the problem.
> >>>
> >>> Tested the fix on a powerpc-e300c3-linux-gnu cross.  Bootstrapped and tested on
> >>> powerpc64le-linux-gnu with no regressions.  Is this okay for trunk?
> >> Okay.
> > No, as I said before this is not correct, not without a lot more
> > explanation at least.  We should not copy errors in the old code into
> > the new code.  That is negating one of the main advantages of
> > reimplementing this in the first place!
> 
> Can you please be more specific?
> 
> All I have from you before is "It should work for 32-bit though?"  I responded in the
> bug report that __builtin_darn_32 was used for this purpose.  I haven't seen a
> response to that.  What do you want to see happen?

That of course does not work for _raw.

These builtins should just return a "long", just like __builtin_ppc_mftb
does.  All three of them.

> The patterns in rs6000.md are darn_32, gated by TARGET_P9_MISC; darn_raw, gated by
> TARGET_P9_MISC && TARGET_64BIT; and darn, gated by TARGET_P9_MISC && TARGET_64BIT.
> The builtins correspond to these patterns in the obvious way.
> 
> If you think that these patterns should be enabled differently, that's fine, but
> that's a completely different patch than fixing the incorrect built-ins to match
> what the patterns do and thus avoid ICEing.

Avoiding ICEs should not be a goal.  It should be a side effect of doing
the right thing in the first place!


Segher