[PATCH] D57240: [RISCV] Don't incorrectly force relocation for %pcrel_lo

[Lewis Revill via Phabricator via llvm-commits]

lewis-revill added a comment.

In D57240#1385261 <https://reviews.llvm.org/D57240#1385261>, @jrtc27 wrote:

> Could we not have a situation where the pcrel_hi20 is seen *after* the lo12, in which case the lo12 would be forced but the hi20 could still be evaluated? E.g. I think the following would be problematic:
>
>   foo:
>       j 1f
>   0:  addi a0, a0, %pcrel_lo(1f)
>       ret
>   1: auipc a0, %pcrel_hi(bar)
>       j 0b
>  
>   .align 2
>   bar:
>       # ...
>
>
> Obviously extremely pathological code, but nonetheless valid.


Good call. It's a pathological case but maybe there are other cases as well. It's not a nice situation. Somehow we have to ensure there can never be a pcrel_lo12 relocation without a corresponding pcrel_hi20 relocation. It might help to know whether the pcrel_hi20 has been seen at all, regardless of whether it was resolved.

So I guess the intended behaviour might be:

pcrel_hi20 seen and not resolved (IE relocation emitted) -> force relocation
pcrel_hi20 seen and resolved -> don't force relocation
pcrel_hi20 not seen -> don't force relocation? If evaluatePcRelLo thinks it can be evaluated does it matter if the pcrel_hi20 can or not?

I'll have another think and take a look at your testcase.


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https://reviews.llvm.org/D57240