[LLVMdev] Handling of KILL instructions.

[Vasileios Kalintiris]

Hi all,

My understanding is that we keep around KILL instructions in order to keep
the results of the various register liveness analysis passes valid.

Consider for example the following machine basic block:

BB#0: derived from LLVM BB %entry
    Live Ins: %A0_64 %A1_64
        %V0_64<def> = AND64 %A0_64<kill>, %A1_64<kill>
        %V0<def> = KILL %V0, %V0_64<imp-use,kill>
        PseudoReturn64 %RA_64

In this case we would like to move the AND64 instruction after the KILL
instruction (generated from an identity COPY).

What is the right thing to do with the KILL instruction given the fact that
the machine function pass calls TRI.invalidateLiveness()? Can we simply
delete any KILL instruction we want? Or, can we ignore them as long as we
don't request any register liveness analysis in subsequent machine function
passes?

-- Vasileios Kalintiris