Re: [avr] gas support for cfi info

[Richard Henderson <rth@redhat.com>]

On 02/22/2011 08:17 AM, Anitha Boyapati wrote:
> Just to be on same page, these are the 2 places:
> 
> 1. gen_enable_interrupt()
> 2. gen_call_prologue_saves()
> 
> 
> For the latter, can you  explain why adding reg notes is required?
> 
> +      add_reg_note (insn, REG_CFA_ADJUST_CFA,
> +		    gen_rtx_SET (VOIDmode,
> +				 (frame_pointer_needed
> +				  ? frame_pointer_rtx : stack_pointer_rtx),
> +				 plus_constant (stack_pointer_rtx,
> +						-(size + live_seq))));
> +
> 
> (The comment does say that this is to describe the effect of
> UNSPEC_VOLATILE, but how reg notes help?)

The external function call represented by the prologue_saves unspec
saves registers to the stack, and allocates stack space.  Both of
these actions are things we want to describe in unwind info.  The
reg notes I added describe all of the actions performed by the
function call.

>>  (2) At present it's possible to use epilogue_restores without
>>      having used prologue_saves.  I.e. use epilogue_restores with
>>      an inline prologue.  The problem being that the inline prologue
>>      uses an HImode push of REG_Y (i.e. r29 first), whereas the code
>>      in prologue_saves pushes r28 first and epilogue_restores is
>>      written to expect that.
>>
> 
> Is this is the line being referred to ?
> 
> if (frame_pointer_needed)
>   {
> ...
>    /* Push frame pointer.  */
> insn = emit_move_insn (pushword, frame_pointer_rtx);

Yes.


r~