[RFC] Cleanup DW_CFA_GNU_args_size handling

[Ulrich Weigand]

Richard Henderson wrote:

>  	  emit_stack_restore (SAVE_BLOCK, old_stack_level);
>  	  stack_pointer_delta = old_stack_pointer_delta;
> +
> +	  /* ??? Is this assert warrented, given emit_stack_restore?
> +	     or should we just mark the last insn no matter what?  */
> +	  last = get_last_insn ();
> +	  set = single_set (last);
> +	  gcc_assert (set != NULL);
> +	  gcc_assert (SET_DEST (set) == stack_pointer_rtx);

This assert triggers on spu-elf, because our restore_stack_block
pattern emits something else as its last instruction: we restore
a stack backchain link after restoring the stack pointer.

Even if we were to swap the order to restore the backchain first,
like rs6000 does, the assert would still trigger, since we cannot
use stack_pointer_rtx to restore the stack pointer; this is because
on SPU, the stack pointer is a vector register, and the ABI says to
maintain the remaining free stack space in a high slot of that
vector.  Therefore, restore_stack_block uses a vector add into
a register generated via gen_rtx_REG (V4SImode, STACK_POINTER_REGNUM)
instead of just plain stack_pointer_rtx ...

Was this assert intended to impose requirements on target's
restore_stack_block implemtations?  What exactly are those
supposed to be?

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com