[PATCH] Make frame saves identical for setjmp and non_local_goto in function.c

[Richard Guenther]

On Thu, 22 May 2008, Andy H wrote:

> This very simple  patch corrects an anomaly in the generation of non-local
> goto information.
> 
> The patch makes the saved frame value identical for both  nested function
> gotos and setjmps.
> 
> As no gcc hosted target (yet) uses TARGET_BUILTIN_SETJMP_FRAME_VALUE, the
> change has no effect.
> However, it is a prerequisite  to correct AVR setjmp problems with an optimal
> solution.
> 
> If this is acceptable change, please approve for 4.4 mainline.
> 
> best regards
> 
> 
> Background
> ------------
> 
> To perform either setjmp or goto from a nested function, the frame and stack
> pointers are saved in buffer.
> 
> This pointer save code is created in two places.
> 
> 1) For setjmp  it is created by expand_builtin_setjmp_setup
> 2) For nested function goto  it is created by: expand_function_start
> 
> For setjmp the frame pointer value is saved using:
> 
>    emit_move_insn (mem, targetm.builtin_setjmp_frame_value ())
> 
> However, expand_function_start uses:
> 
>      emit_move_insn (r_save, virtual_stack_vars_rtx)
> 
> As both use same goto/receiver code they should  to be identical. This works
> only because of the default :
> for TARGET_BUILTIN_SETJMP_FRAME_VALUE  is  virtual_stack_vars_rtx
> 
> This target hook  allows the true value of the frame_pointer to be saved and
> restored. Whereas
> virtual_stack_vars_rtx will incur addition and subtraction overheads if
> STARTING_FRAME_OFFSET !=0.
> However, because of the mismatch any  attempt  to utilise this hook, will
> cause either goto or setjmp to fail.
> 
> In the AVR target, this is the case and  I wish to set
> 
> setjmp_frame_value = virtual_stack_vars_rtx - STARTING_FRAME_OFFSET
> 
> which eliminate add/sub operations on frame pointer and minimizes the receiver
> code to nothing.
> (and allow me to fix another bug)

And you tested this on ... ?

Otherwise this is ok for mainline.

Thanks,
Richard.


> 2008-05-22    Andy Hutchinson   <hutchinsonandy@aim.com>
> 
>  *  gcc/function.c: Include target hook for nonlocal_goto frame value.