[LLVMdev] Q about instruction pattern matching

[Evan Cheng]

On Oct 1, 2007, at 12:09 AM, Andreas Fredriksson wrote:

> On 10/1/07, Evan Cheng <evan.cheng at apple.com> wrote:
>
>>> If I lower the calling convention stuff manually rather than relying
>>> on the generated CC analyzer, how do I determine that a formal
>>> argument I'm about to receive or pack together is supposed to be  
>>> used
>>> as a pointer so I can stick it in an address register?
>>
>> I'd suggest custom lowering for now. Again use data registers during
>> lowering and fix them during the isel post pass if the parameters are
>> used as pointers. Do you think that would work?
>
> I guess in a regparm ABI like the one I'm targeting, LLVM will produce
> "live ins" for the registers that are used in the ABI in the entry
> basic block of all functions? I've seen "Live ins: D0" appear for an
> int (int)-type signature, so that seems right.

Right.

> I'd like to arrange for e.g. a void foo(char*p) signature so see a
> "live in A0", but can I custom lower to that immediately given that
> I'm going to do a tapdance with the instruction selections later on?
> If not, how do I distinguish these arguments from the data argument
> later on?

Hrm. I suspect you'll have to add parameter attribute (see  
ParameterAttributes.h) that indicates it's used as an address. In  
SelectionDAGIsel.cpp:TargetLowering::LowerAguments(), you have access  
to the function argument type. Anyone sees an alternative solution?

Evan

>
> Thanks,
> Andreas
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