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

[Kan Shengchen via Phabricator via llvm-commits]

skan added inline comments.


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Comment at: llvm/test/CodeGen/X86/peephole-na-phys-copy-folding.ll:376
   %cmp = icmp sgt i32 %val, 0
   %res = tail call i32 asm "bsfl $1,$0", "=r,r,~{cc},~{dirflag},~{fpsr},~{flags}"(i32 %val)
   store i32 %res, ptr %mem, align 4
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aaronpuchert wrote:
> pengfei wrote:
> > aaronpuchert wrote:
> > > Goes a bit too far I think. We can turn a generic builtin into `rep; bsf`, but if the inline assembly explicitly asks for `bsf` I think we should emit that.
> > You are right. So this is to check *no* REP prefix was generated. :)
> Sorry, I missed the `-NOT`. But is that needed? After all the `-NEXT` shouldn't match if there is a `rep` in between.
> 
> If there is a reason to keep this, the second occurrence should likely be `CHECK64` instead of `CHECK32`.
I think the two `CHECK-NOT` are redundant here b/c `CHECK-NEXT` can gurantee `#APP` is followed by `bsfl`.


Repository:
  rG LLVM Github Monorepo

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

https://reviews.llvm.org/D130956