[PATCH 3/5] regrename: Don't rename restores

Jeff Law law@redhat.com
Mon Sep 26 16:44:00 GMT 2016


On 09/23/2016 02:21 AM, Segher Boessenkool wrote:
> A restore is supposed to restore some certain register.  Restoring it
> into some other register will not work.  Don't.
>
>
> 2016-09-23  Segher Boessenkool  <segher@kernel.crashing.org>
>
> 	* regrename.c (build_def_use): Invalidate chains that have a
> 	REG_CFA_RESTORE on some instruction.
>
> ---
>  gcc/regrename.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/gcc/regrename.c b/gcc/regrename.c
> index 54c7768..00a5d02 100644
> --- a/gcc/regrename.c
> +++ b/gcc/regrename.c
> @@ -1867,6 +1867,12 @@ build_def_use (basic_block bb)
>  		scan_rtx (insn, &XEXP (note, 0), NO_REGS, terminate_dead,
>  			  OP_IN);
>  	      }
> +
> +	  /* Step 8: Kill the chains involving register restores.  Those
> +	     should restore _that_ register.  */
> +	  for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
> +	    if (REG_NOTE_KIND (note) == REG_CFA_RESTORE)
> +	      scan_rtx (insn, &XEXP (note, 0), NO_REGS, mark_all_read, OP_IN);
>  	}
>        else if (DEBUG_INSN_P (insn)
>  	       && !VAR_LOC_UNKNOWN_P (INSN_VAR_LOCATION_LOC (insn)))
Seems like a good thing regardless of the shrink-wrapping changes. 
There's a comment about 200 lines earlier (egad) which outlines the 
steps.  Can you please add a comment there too.

It would probably be a good idea to refactor build_def_use a bit, but 
I'd understand if you don't want to tackle that.  I don't think that 
desire should block this patch.

As I've said before, I'm not sure we're getting CFA notes right, 
particularly on the older ports, but I don't think that should block 
this patch.


With the earlier comment update change this is OK.

jeff



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