[PATCH] D86260: [CodeGen] Postprocess PHI nodes for callbr

[James Y Knight via Phabricator via llvm-commits]

jyknight added a comment.

In D86260#2229406 <https://reviews.llvm.org/D86260#2229406>, @void wrote:

> In D86260#2229387 <https://reviews.llvm.org/D86260#2229387>, @jyknight wrote:
>
>> The commit message is confusing for this -- this isn't a correctness fix, but a minor optimization, right?
>
> I'm not convinced it's just an optimization, but I could be swayed. It seems to me that the value coming into the PHI shouldn't rely upon the semantics of the asm block. So for instance would this be incorrect?

Inline assembly must declare what registers it clobbers, and the compiler can safely assume other registers are preserved across it.

>   bb1:
>     %eax = MOV 0
>     INLINEASM_BR "mov 37, %eax"
>     JMP return
>   
>   return:
>     PHI bb1, 0 ...

So, in this example the input inline-asm is invalid, because it failed to declare that it clobbered eax.


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https://reviews.llvm.org/D86260