[llvm-commits] Trampoline support (pointers nested funtions)

[Chris Lattner]

On Jul 31, 2007, at 3:08 PM, Evan Cheng wrote:

>>> Also, isn't the static chain register described in  
>>> X86CallingConv.td?
>>
>> It is, but it's hard to use here.  The problem is that when  
>> lowering the
>> init.trampoline intrinsic you only have a pointer to the target  
>> function.
>> From this pointer you would like to find out which register a certain
>> parameter will be passed in for that function.  Not so easy!  It's  
>> like
>> having a call instruction without having the arguments.  In order to
>> exploit X86CallingConv.td, you have to use all the lowering  
>> machinery,
>> which isn't adapted to this case.  For example, you could try to  
>> synthesize
>> a fake call.  Or you could pretend to be lowering the target  
>> function.  I
>> tried it, and it can be done with a lot of horrible hacking.  But  
>> it's not
>> worth it.  It's much simpler to simply grab the calling convention  
>> and use
>> that, which unfortunately means keeping LowerTRAMPOLINE and
>> X86CallingConv.td in sync.  Personally I can live with that,  
>> especially since
>> I've seen the alternative and it still wakes me up screaming at  
>> night :)
>> But maybe you can see a reasonable way of doing it?
>
> Seems like a deficiency in CCState class. Chris, your thoughts?

Isn't the argument always a pointer, and thus always the same thing  
for a particular calling conv?

-Chris