[PATCH] D116424: [ShrinkWrap] check for PPC's non-callee-saved LR

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

In D116424#3223526 <https://reviews.llvm.org/D116424#3223526>, @nickdesaulniers wrote:

> In D116424#3223345 <https://reviews.llvm.org/D116424#3223345>, @efriedma wrote:
>
>> Do we need coverage for lr use and/or def, in addition to clobber?
>
> Can you help me come up with test cases? :-3

Oh, I assumed it was working based on other testcases in this file.  I guess it actually isn't.  (There are in-tree testcases with an "lr" output, but they discard the output value.)

I'm a little concerned that isEarlyClobber() won't handle this correctly if it ever does get implemented, but I guess we can leave that for a followup, if anyone hacking on the PPC backend is interested.

> I would have guessed for a use+def:
>
>   void x (void) {
>       register int y asm("lr");
>       asm (""::"r"(y));
>   }
>
> but that actually asserts during post-RA pseudo expansion: `Impossible reg-to-reg copy` (probably we're missing support for `mfspr`?).

Yes, probably copies just aren't implemented.


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