var-tracking and s390's LM(G)

[Jakub Jelinek]

On Tue, Feb 04, 2014 at 03:38:51PM +0000, Richard Sandiford wrote:
> What do you want var-tracking to do about the __builtin_eh_return case
> though?  It isn't correct to say that the instruction adds the frame size
> to the stack pointer then, since the loaded value includes the eh_return
> adjustment.  Pretending it is a constant addition in order to satisfy the
> sanity check seems a bit hackish, but there again it'd be a shame to lose
> tracking for the whole function just because of that.

For __builtin_eh_return the unwind info starting with restoring the stack
pointer to the landing pad's stack pointer until you actually return/jump to the
landing pad is wrong in either case, not just on s390, but on various other
targets.  Saying REG_CFA_ADJUST_CFA by the frame size will result in CFA
from that point being stack_pointer + 160, which is exactly what you are
doing anyway, the DW_CFA_offset 15, ... and DW_CFA_restore aren't helpful to
that at all and don't change anything on it.

Unless you have the old value of the stack pointer saved in some hard
register, providing correct unwind info there is not possible.

	Jakub