[llvm-dev] How to create and insert a call MachineInstr?

[Will Lester via llvm-dev]

Thanks for your help! I'm much more clear about this problem.
Will

2018-04-13 17:53 GMT+08:00 Tim Northover <t.p.northover at gmail.com>:

> Hi Will,
>
> On 13 April 2018 at 09:50, Will Lester via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > I have used BuildMI to build a MachineInstr. But it seems that a call
> > MachineInstr only has one parameter which is a
> > register(%physreg44<imp-use>?).
>
> This depends on the target, but calls normally have a few operands:
>
>   + The callee (a register or a global address or something).
>   + A regmask indicating which registers the call preserves.
>   + A list of imp-uses and imp-defs for the registers used to pass and
> return parameters.
>
> If you writie a .ll file that makes a call you should be able to see
> all these components in the generated MIR.
>
> > Therefore how can I set the callee function and the arguments of the
> function?
>
> For a direct call, you'd normally use MachineInstrBuilder's
> addGlobalAddress to set the callee. You have to emit separate moves
> and stores before the call to put the arguments in the correct
> registers and stack slots. Be careful not to clobber live registers!
>
> We can probably give a few more details (like the call instruction to
> use, and which registers pass parameters; maybe some extra quirks) if
> we know the actual target you're compiling for, but the outline above
> won't change significantly.
>
> Cheers.
>
> Tim.
>
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