Re: [PATCH] Use signed boolean type for boolean vectors

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Oct 28, 2015 at 2:13 PM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
> Hi,
>
> Testing boolean vector conversions I found several runtime regressions
> and investigation showed it's due to incorrect conversion caused by
> unsigned boolean type.  When boolean vector is represented as an
> integer vector on target it's a signed integer actually.  Unsigned
> boolean type was chosen due to possible single bit values, but for
> multiple bit values it causes wrong casting.  The easiest way to fix
> it is to use signed boolean value.  The following patch does this and
> fixes my problems with conversion.  Bootstrapped and tested on
> x86_64-unknown-linux-gnu.  Is it OK?

Hmm.  Actually formally the "boolean" vectors were always 0 or -1
(all bits set).  That is also true for a signed boolean with precision 1
but with higher precision what makes sure to sign-extend 'true'?

So it's far from an obvious change, esp as you don't change the
precision == 1 case.  [I still think we should have precision == 1
for all boolean types]

Richard.

> Thanks,
> Ilya
> --
> gcc/
>
> 2015-10-28  Ilya Enkovich  <enkovich.gnu@gmail.com>
>
>         * optabs.c (expand_vec_cond_expr): Always get sign from type.
>         * tree.c (wide_int_to_tree): Support negative values for boolean.
>         (build_nonstandard_boolean_type): Use signed type for booleans
>         with precision greater than 1.
>
>
> diff --git a/gcc/optabs.c b/gcc/optabs.c
> index e1ac0b8..37a67f1 100644
> --- a/gcc/optabs.c
> +++ b/gcc/optabs.c
> @@ -5373,7 +5373,6 @@ expand_vec_cond_expr (tree vec_cond_type, tree op0, tree op1, tree op2,
>        op0a = TREE_OPERAND (op0, 0);
>        op0b = TREE_OPERAND (op0, 1);
>        tcode = TREE_CODE (op0);
> -      unsignedp = TYPE_UNSIGNED (TREE_TYPE (op0a));
>      }
>    else
>      {
> @@ -5382,9 +5381,9 @@ expand_vec_cond_expr (tree vec_cond_type, tree op0, tree op1, tree op2,
>        op0a = op0;
>        op0b = build_zero_cst (TREE_TYPE (op0));
>        tcode = LT_EXPR;
> -      unsignedp = false;
>      }
>    cmp_op_mode = TYPE_MODE (TREE_TYPE (op0a));
> +  unsignedp = TYPE_UNSIGNED (TREE_TYPE (op0a));
>
>
>    gcc_assert (GET_MODE_SIZE (mode) == GET_MODE_SIZE (cmp_op_mode)
> diff --git a/gcc/tree.c b/gcc/tree.c
> index e77d4b8..712390f 100644
> --- a/gcc/tree.c
> +++ b/gcc/tree.c
> @@ -1451,7 +1451,7 @@ wide_int_to_tree (tree type, const wide_int_ref &pcst)
>         case BOOLEAN_TYPE:
>           /* Cache false or true.  */
>           limit = 2;
> -         if (hwi < 2)
> +         if (IN_RANGE (hwi, 0, 1))
>             ix = hwi;
>           break;
>
> @@ -8076,7 +8076,10 @@ build_nonstandard_boolean_type (unsigned HOST_WIDE_INT precision)
>
>    type = make_node (BOOLEAN_TYPE);
>    TYPE_PRECISION (type) = precision;
> -  fixup_unsigned_type (type);
> +  if (precision > 1)
> +    fixup_signed_type (type);
> +  else
> +    fixup_unsigned_type (type);
>
>    if (precision <= MAX_INT_CACHED_PREC)
>      nonstandard_boolean_type_cache[precision] = type;