[PATCH] D130956: [X86][MC] Always emit `rep` prefix for `bsf`

Wed Aug 3 14:54:22 PDT 2022

craig.topper added a comment.

In D130956#3697870 <https://reviews.llvm.org/D130956#3697870>, @fmayer wrote:

> In D130956#3697869 <https://reviews.llvm.org/D130956#3697869>, @craig.topper wrote:
>
>> I'll revert, I'll have to do a fixup for a dependent patch that I committed after this.
>
> Thanks! I can also verify that a revert actually fixes this, but judging from the Changes in the first build that introduced the failure, I think it's very likely that it was this.

It was definitely this. The `ffs` in the name of the failing function is 'find first set' bit. That's what the bsf and tzcnt instructions do.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D130956/new/

https://reviews.llvm.org/D130956