Re: RFC/CFT: Patch to fix the PowerPC var-tracking.c failure

[Eric Botcazou <ebotcazou at libertysurf dot fr>]

> The idea is to use PSEUDO_REGNO_MODE (ORIGINAL_REGNO ...) to detect
> cases where a register was a paradoxical subreg of a psuedo before
> reload.  In that case, the REG_ATTRS of the post-reload register pretend
> that the whole register contains useful information, whereas in reality
> only the original inner register did.  We can then create a
> representation of the original inner register with approriately-narrowed
> REG_ATTRS.  This is the right behaviour for MO_USE, MO_SET and MO_COPY
> -- all of which are associated with locations that have trackable
> attributes -- but not for MO_USE_NO_VAR and MO_CLOBBER, which record
> attributeless uses or clobbers of the whole register.

This sounds sensible to me.

> Adjusting the rtx of a MO_SET and MO_COPY like this means that we
> need to adjust any useful SET_SRC in the same way.  The current code
> goes to great lengths to try to find the original SET_SRC (sometimes
> considering COND_EXECs and sometimes not; I'm not sure if that's
> deliberate) but it's more convenient to create the new SET_SRC at the
> same time as the new SET_DEST.  The patch therefore records a SET rather
> than a destination if both the SET_DEST and SET_SRC are useful.

Likewise.  The authors of var-tracking.c might want to comment on this though.

> 	* dse.c (find_shift_sequence): Reinstate "<= UNITS_PER_WORD" condition.
> 	* var-tracking.c (micro_operation_def): Update comment on u.loc.
> 	(mode_for_reg_attrs, var_lowpart): New functions.
> 	(add_uses): Consider recording a lowpart of LOC for MO_USE.
> 	(add_stores): Likewise MO_SET and MO_COPY.  If the source of a set
> 	or copy is known, set LOC to the SET that performs the set, instead
> 	of the destination.
> 	(find_src_status, find_src_set_src): Remove LOC parameter.
> 	Replace INSN with the source value.
> 	(compute_bb_dataflow, emit_notes_in_bb): Check for a SET u.loc when
> 	handling MO_SET and MO_COPY.  Update the calls to find_src_status
> 	and find_src_set_src.

OK, modulo

> @@ -1767,16 +1824,35 @@ add_stores (rtx loc, const_rtx expr, voi
>        if (GET_CODE (expr) == CLOBBER
>
>  	  || ! REG_EXPR (loc)
>  	  || ! track_expr_p (REG_EXPR (loc)))
>
> -	mo->type = MO_CLOBBER;
> -      else if (GET_CODE (expr) == SET
> -	       && SET_DEST (expr) == loc
> -	       && same_variable_part_p (SET_SRC (expr),
> -					REG_EXPR (loc),
> -					REG_OFFSET (loc)))
> -	mo->type = MO_COPY;
> +	{
> +	  mo->type = MO_CLOBBER;
> +	  mo->u.loc = loc;
> +	}
>        else
> -	mo->type = MO_SET;
> -      mo->u.loc = loc;
> +	{
> +	  enum machine_mode mode = mode_for_reg_attrs (loc);
> +	  rtx src = NULL;
> +
> +	  if (GET_CODE (expr) == SET && SET_DEST (expr) == loc)
> +	    src = var_lowpart (mode, SET_SRC (expr));
> +	  loc = var_lowpart (mode, loc);
> +
> +	  if (src == NULL)
> +	    {
> +	      mo->type = MO_SET;
> +	      mo->u.loc = loc;
> +	    }
> +	  else
> +	    {
> +	      if (SET_SRC (expr) != src)
> +		expr = gen_rtx_SET (VOIDmode, loc, src);
> +	      if (same_variable_part_p (src, REG_EXPR (loc), REG_OFFSET (loc)))
> +		mo->type = MO_COPY;
> +	      else
> +		mo->type = MO_SET;
> +	      mo->u.loc = CONST_CAST_RTX (expr);
> +	    }
> +	}
>        mo->insn = (rtx) insn;
>      }
>    else if (MEM_P (loc)
> @@ -1787,49 +1863,41 @@ add_stores (rtx loc, const_rtx expr, voi
>        micro_operation *mo = VTI (bb)->mos + VTI (bb)->n_mos++;
>
>        if (GET_CODE (expr) == CLOBBER)
> -	mo->type = MO_CLOBBER;
> +	{
> +	  mo->type = MO_CLOBBER;
> +	  mo->u.loc = loc;
> +	}
>        else if (GET_CODE (expr) == SET
>  	       && SET_DEST (expr) == loc
> -	       && same_variable_part_p (SET_SRC (expr),
> -					MEM_EXPR (loc),
> -					MEM_OFFSET (loc)
> -					? INTVAL (MEM_OFFSET (loc)) : 0))
> -	mo->type = MO_COPY;
> +	       && var_lowpart (GET_MODE (loc), SET_SRC (expr)))
> +	{
> +	  if (same_variable_part_p (SET_SRC (expr),
> +				    MEM_EXPR (loc),
> +				    MEM_OFFSET (loc)
> +				    ? INTVAL (MEM_OFFSET (loc)) : 0))
> +	    mo->type = MO_COPY;
> +	  else
> +	    mo->type = MO_SET;
> +	  mo->u.loc = CONST_CAST_RTX (expr);
> +	}
>        else
> -	mo->type = MO_SET;
> -      mo->u.loc = loc;
> +	{
> +	  mo->type = MO_SET;
> +	  mo->u.loc = loc;
> +	}
>        mo->insn = (rtx) insn;
>      }
>  }

Please use the same structure if the MEM case as in the REG case:

      else
	{
	  rtx src = NULL;

	  if (GET_CODE (expr) == SET && SET_DEST (expr) == loc)
	    src = var_lowpart (GET_MODE (loc), SET_SRC (expr));

	  if (src == NULL)
	    {
	      mo->type = MO_SET;
	      mo->u.loc = loc;
	    }
	  else
	    {
	  if (same_variable_part_p (SET_SRC (expr),
				    MEM_EXPR (loc),
				    MEM_OFFSET (loc)
				    ? INTVAL (MEM_OFFSET (loc)) : 0))
	    mo->type = MO_COPY;
	  else
	    mo->type = MO_SET;
	  mo->u.loc = CONST_CAST_RTX (expr);
	}

-- 
Eric Botcazou