[LLVMdev] Var Args on X86-64

[David Meyer]

Hello all,

I wish to get the va_arg instruction working on X86-64 Linux.  This requires
implementing VAARG lowering for X86-64.

I am fine with implementing it, but I am unsure of what approach I should
take. The straightforward option is to add the DAG nodes required to perform
the operation during lowering. (in X86TargetLowering::LowerVAARG()).
 However, the resulting code will be relatively long to accommodate the
complexity of what va_arg must do. It would be easier to operate on a higher
level, for example, by implementing va_arg in LLVM assembly. Is it possible
(or preferable) to implement an intrinsic (va_arg) using target-specific
llvm assembly?

Thanks,
 David M
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