[PATCH, i386, Pointer Bounds Checker 31/x] Pointer Bounds Checker builtins for i386 target

[Uros Bizjak]

On Thu, Oct 9, 2014 at 4:07 PM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
> It appeared I changed a semantics of BNDMK expand when replaced tree operations with rtl ones.
>
> Original code:
>
> +      op1 = expand_normal (fold_build2 (PLUS_EXPR, TREE_TYPE (arg1),
> +                                       arg1, integer_minus_one_node));
> +      op1 = force_reg (Pmode, op1);
>
> Modified code:
>
> +      op1 = expand_normal (arg1);
> +
> +      if (!register_operand (op1, Pmode))
> +       op1 = ix86_zero_extend_to_Pmode (op1);
> +
> +      /* Builtin arg1 is size of block but instruction op1 should
> +        be (size - 1).  */
> +      op1 = expand_simple_binop (Pmode, PLUS, op1, constm1_rtx,
> +                                op1, 1, OPTAB_DIRECT);
>
> The problem is that in the fixed version we may modify value of a pseudo register into which arg1 is expanded which means incorrect value for all following usages of arg1.
>
> Didn't reveal it early because programs surprisingly rarely hit this bug.  I do following change to fix it:
>
>        op1 = expand_simple_binop (Pmode, PLUS, op1, constm1_rtx,
> -                                op1, 1, OPTAB_DIRECT);
> +                                NULL, 1, OPTAB_DIRECT);
>
> Similar problem was also fixed for BNDNARROW.  Does it look OK?

I'm not aware of this type of limitation, and there are quite some
similar constructs in i386.c. It is hard to say without the testcase
what happens, perhaps one of RTX experts (CC'd) can advise what is
recommended here.

Uros.