[llvm-dev] Can DBG_VALUE instructions use undefined vregs?

Tue Oct 5 15:37:02 PDT 2021

I can't really be speak about debug instructions in particular. For machine instructions in general you just mark the use operand with "undef" and you are good...

- Matthias

> On Oct 5, 2021, at 3:29 PM, Amara Emerson via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> One GlobalISel compile time optimization patch (https://reviews.llvm.org/D109750) has generated some debate over whether it’s semantically allowed/not-an-error for a DBG_VALUE machine instruction to have a use of a vreg that doesn’t have a corresponding definition.
> 
> We talked internally with Adrian and Vedant and didn’t come to a strong conclusion either way. Does anyone have thoughts here?
> 
> Thanks,
> Amara
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