[llvm] [RDF] Create phi nodes for clobbering defs (PR #123694)

[Krzysztof Parzyszek via llvm-commits]

kparzysz wrote:

As far as I remember clobbering defs don't have reached uses.  They act as "undefs", i.e. putting some indeterminate value in the register.  Using such a register is equivalent to using an undefined one.

I also vaguely recall doing something like this in the past, could you look through the git log for this file to see if there is anything in there that could be related to your changes?  The large number of phi nodes was definitely a problem a while back.

Could you elaborate a bit more about what kind of an issue was this causing?

Thanks for looking into this.

https://github.com/llvm/llvm-project/pull/123694