[llvm-commits] [llvm] r95351 - in /llvm/trunk: lib/Target/X86/X86ISelLowering.cpp test/CodeGen/X86/tailcall2.ll

[Duncan Sands]

Hi Evan,

> Handle tail call with byval arguments.

if you have a tail call with byval arguments, does this mean that an extra copy
of the byval argument won't be made?  This came up with the C++ thunk
implementation in dragonegg, where you can get this kind of thing:

define void @f_thunk(xyz *%this, %struct *%x byval) {
... adjust %this ...
   tail call void @f(xyz *%new_this, %struct *%x byval)
}

It would be nice if this didn't result in a second copy of %x being made
on the stack when calling @f.  Is this the case?

Thanks,

Duncan.

PS: To be honest, I don't mark the call to @f "tailcall" because I was worried
that it is invalid to do, since after all the byval argument creates a stack
object which is used by the callee, which is exactly what tail calls are not
supposed to do...  On the other hand, the optimizers happily mark @f "tailcall",
but I suspect that's because the tailcall optimization pass doesn't know about
byval, and not because it is being clever...