[PATCH] D132073: [CodeGen] Zero out only modified registers

Thu Sep 1 15:16:38 PDT 2022

efriedma added a comment.

In D132073#3765379 <https://reviews.llvm.org/D132073#3765379>, @void wrote:

> In D132073#3765159 <https://reviews.llvm.org/D132073#3765159>, @efriedma wrote:
>
>>> we shouldn't be zeroing %rdi
>>
>> I don't see how it's a problem if we zero rdi.  Even if we don't modify rdi, the caller doesn't have any way of knowing it wasn't modified.  The calling convention says it's caller-save.
>
> This is just a test case. It's not meant to be definitive of the original bug. Just show the same symptoms.

The thing is, I don't see the connection between this "symptom" and any possible bug.  rdi is callee-clobbered, and the caller has no way of knowing whether the implementation actually writes to rdi, therefore it can't be a bug to add a write to rdi.

Repository:
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  https://reviews.llvm.org/D132073/new/

https://reviews.llvm.org/D132073