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...lower using the IR simplification passes [2]. Renderscript is an example of another project that uses IR as a stable distribution format, though I think currently Renderscript is not subsetting IR much. Some examples of PNaCl's IR simplification passes are: * Calling conventions lowering: ExpandVarArgs and ExpandByVal lower varargs and by-value argument passing respectively. They would be useful for any backend that doesn't want to implement varargs or by-value calling conventions. * Instruction-level lowering: * ExpandStructRegs splits up struct values into scalars, removing the &quot...

...e simplify writing a backend, should there be commensurate >> changes to any relevant documentation for getting started writing >> backends? (we don't have much such documentation though...) > > Very much so, yes. And this... >>>> * Calling conventions lowering:  ExpandVarArgs and ExpandByVal >>>> lower varargs and by-value argument passing respectively. >>>> They would be useful for any backend that doesn't want to >>>> implement varargs or by-value calling conventions. >>> >>> Why wouldn't these be applicabl...

...ysis of the IR more straight-forward. However, va_arg can't currently be used with an aggregate type (such as a struct). The difficulty of adding support for aggregates is discussed later in this email. Which Clang targets generate va_arg? * PNaCl always uses va_arg, even for aggregates. Their ExpandVarArgs pass replaces it with appropriate loads and stors. * AArch64/Darwin generates va_arg if possible. When not possible, as for aggregates or illegal vector types, it generates the usual va_list manipulation code. It is not used for other AARch64 platforms. * A few other targets such as MSP430, Lanai a...

...cific passes you mention. Perhaps > these questions are better answered in the review thread for the patches, > but they are at least things that I would think about and try to address if > and when you send out the code review. > > >> >> * Calling conventions lowering: ExpandVarArgs and ExpandByVal lower >> varargs and by-value argument passing respectively. They would be useful >> for any backend that doesn't want to implement varargs or by-value calling >> conventions. >> > > Why wouldn't these be applicable to existing backends? What i...