Signedness of boolean types (and Ada)

[Eric Botcazou]

> I noticed while debugging why my "A?CST1:CST0" patch was broken for
> Ada, I noticed the following ranges for boolean types:
>   # RANGE [0, 1] NONZERO 1
>   _14 = checks__saved_checks_tos.482_2 > 0;
>   # RANGE [0, 255] NONZERO 1
>   _18 = _14 == 0;
>   _19 = ~_18;

The '~' looks problematic if this is for Ada code, it ought to be:

  _19 = _18 ^ 1;

See below.

> Should TYPE_UNSIGNED be always set for boolean types?
> 
> I am testing the below patch to see if it fixes the problem, if we
> should assume TYPE_UNSIGNED is true for boolean types.  If we should
> not assume that, then there is a problem with conversion between
> boolean types that have TYPE_UNSIGNED mismatched.

The patch is a nop, boolean types are always unsigned in Ada, see cstand.adb:

      Set_Is_Unsigned_Type (Standard_Boolean);

but they have 8-bit precision instead of 1-bit precision so must be handled 
with care, in particular BIT_NOT_EXPR should be avoided for them, see e.g. the 
gimplifier:

	    if (TYPE_PRECISION (TREE_TYPE (*expr_p)) == 1)
	      *expr_p = build1_loc (input_location, BIT_NOT_EXPR,
				    TREE_TYPE (*expr_p),
				    TREE_OPERAND (*expr_p, 0));
	    else
	      *expr_p = build2_loc (input_location, BIT_XOR_EXPR,
				    TREE_TYPE (*expr_p),
				    TREE_OPERAND (*expr_p, 0),
				    build_int_cst (TREE_TYPE 
(*expr_p), 1));

-- 
Eric Botcazou