Re: [PATCH] Logical short circuiting with Fortran argument lists

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2018-08-03 05:32, Richard Bunt wrote:
> Logical short circuiting with argument lists
>
> When evaluating Fortran expressions such as the following:
>
> 	print truth_table(1, 1) .OR. truth_table(2, 1)
>
> where truth_table(1, 1) evaluates to true, the debugger would report
> that it could not perform substring operations on this type. This patch
> addresses this issue.
>
> Investigation revealed that EVAL_SKIP was not being handled correctly
> for all types serviced by the OP_F77_UNDETERMINED_ARGLIST case in
> evaluate_subexp_standard. While skipping an undetermined argument
> list the type is resolved to be an integer (as this is what
> evaluate_subexp returns when skipping) and so it was not possible to
> delegate to the appropriate case (e.g. array, function call).
>
> The solution proposed here is to hoist the skip from the function call
> case to apply to all types of argument list.
>
> While this patch allows a wider range of expressions to be evaluated, 
> it
> should be noted that this patch does not allow the skipping of arrays
> which use Fortran array slicing, due to the inability of the debugger
> to skip OP_RANGE.
>
> This patch has been tested with GCC 7.3 on x86_64, aarch64 and ppc64le.

Hi Richard,

Thanks for the patch, hat sounds reasonnable.  Just one question:

> diff --git a/gdb/eval.c b/gdb/eval.c
> index
> 9db6e7c69dad9e674f66991e2aee7dd8d66d80c7..2350c7faaf6221a5990cf5264fe7fe93b4f4be4c
> 100644
> --- a/gdb/eval.c
> +++ b/gdb/eval.c
> @@ -1902,6 +1902,17 @@ evaluate_subexp_standard (struct type 
> *expect_type,
>
>        /* First determine the type code we are dealing with.  */
>        arg1 = evaluate_subexp (NULL_TYPE, exp, pos, noside);
> +
> +      /* Allow the short-circuiting of array accesses, function calls
> +	 and substring operations in logical expressions.  */
> +      if (noside == EVAL_SKIP)
> +	{
> +	  /* Skip all the array subscripts.  */
> +	  for (int i = 0; i < nargs; ++i)
> +	    evaluate_subexp (NULL_TYPE, exp, pos, noside);
> +	  return eval_skip_value (exp);
> +	}
> +
>        type = check_typedef (value_type (arg1));
>        code = TYPE_CODE (type);
>
> @@ -1952,8 +1963,6 @@ evaluate_subexp_standard (struct type 
> *expect_type,
>  	  for (; tem <= nargs; tem++)
>  	    argvec[tem] = evaluate_subexp_with_coercion (exp, pos, noside);
>  	  argvec[tem] = 0;	/* signal end of arglist */
> -	  if (noside == EVAL_SKIP)
> -	    return eval_skip_value (exp);

Is this change needed?  Your test passes even when leaving that part 
as-is.

Thanks,

Simon