[llvm-dev] EFLAGS

[Chris Sears via llvm-dev]

What is the difference between

    Uses = [EFLAGS] + Defs = [EFLAGS]

and their mention in selection patterns?

    [(set GR64:$dst, EFLAGS, (X86smul_flag GR64:$src1, GR64:$src2))]

Basically, my problem is that I have weird instructions which undef the
EFLAGS register, leaving EFLAGS in an unknown state. For example:

    cmp x, y
    beq z           ; this is good because EFLAGS is defined

    cmp x, y
    weird_inst.   ; undefs EFLAGS, leaves EFLAGS in a undefined state
    beq z           ; this is bad because EFLAGS is undefined

Is it enough to just say Defs = [EFLAGS] for the Instruction def of
weird_inst? Or is it necessary for the pattern to say something like [(set
EFLAGS, undef)] as well?
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