[Bug middle-end/98190] [11 Regression] GCC11 miscompiles code using _Bool when inlining: bfxil instruction misused since r11-165

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98190

--- Comment #14 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #12)
> (In reply to rsandifo@gcc.gnu.org from comment #10)
> > If we can't assert, I guess the rule is that we need to extend
> > whenever we're storing to the MSB of the inner register.  We can
> > do that either by extending the source value and the range to
> > the outer register, or by assigning to the inner register and
> > then extending it separately.
> 
> So perhaps:
> --- gcc/expr.c.jj	2020-12-09 00:00:08.622548080 +0100
> +++ gcc/expr.c	2020-12-09 10:36:12.198801940 +0100
> @@ -5451,6 +5451,33 @@ expand_assignment (tree to, tree from, b
>  					       mode1, to_rtx, to, from,
>  					       reversep))
>  	    result = NULL;
> +          else if (SUBREG_P (to_rtx)
> +		   && SUBREG_PROMOTED_VAR_P (to_rtx))
> +	    {
> +	      /* If to_rtx is a promoted subreg, this must be a store to the
> +		 whole variable, otherwise to_rtx would need to be MEM.
> +		 We need to zero or sign extend the value afterwards.  */
> +	      gcc_assert (known_eq (bitpos, 0)
> +			  && known_eq (bitsize,
> +				       GET_MODE_BITSIZE (GET_MODE (to_rtx))));
> +	      if (TREE_CODE (to) == MEM_REF && !REF_REVERSE_STORAGE_ORDER (to))
> +		result = store_expr (from, to_rtx, 0, nontemporal, false);
> +	      else
> +		{
> +		  result = store_field (to_rtx, bitsize, bitpos,
> +					bitregion_start, bitregion_end,
> +					mode1, from, get_alias_set (to),
> +					nontemporal, reversep);
> +		  rtx to_rtx1
> +		    = lowpart_subreg (subreg_unpromoted_mode (to_rtx),
> +				      SUBREG_REG (to_rtx),
> +				      subreg_promoted_mode (to_rtx));
> +		  to_rtx1 = convert_to_mode (subreg_promoted_mode (to_rtx),
> +					     to_rtx1,
> +					     SUBREG_PROMOTED_SIGN (to_rtx));
> +		  emit_move_insn (SUBREG_REG (to_rtx), to_rtx1);
> +		}
> +	    }
>  	  else
>  	    result = store_field (to_rtx, bitsize, bitpos,
>  				  bitregion_start, bitregion_end,
> 
> then?  As in, if store_expr can handle it, use that, otherwise perform the
> extension at the end.
LGTM FWIW, although I shouldn't be the one to review.  I'm not
sure off-hand whether it's OK to store an unpromoted value to
a promoted subreg lhs, with the promoted subreg being temporarily
invalid.  If that's a problem, it might be safer to pass to_rtx1
to store_field instead.