Re: why does c_strlen() return a signed integer?

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, Aug 24, 2018 at 12:16 AM Martin Sebor <msebor@gmail.com> wrote:
>
> PR 87059 - internal compiler error: in set_value_range, at
> tree-vrp.c:289, is apparently due to an argument type mismatch
> in a MIN_EXPR introduced by expand_builtin_strncmp().
>
> The function calls c_strlen() to compute the length of the two
> string arguments to strncmp() and then replaces the third (bound)
> argument with a MIN (len, bound).  The type mismatch is caused by
> len being the signed result of c_strlen(), while bound being
> the size_t argument (explicitly converted to sizetype by
> the function).
>
> My question is: why does c_strlen() return a ssizetype, a signed
> type, rather the more natural sizetype?  I ask in part because
> changing expand_builtin_strncmp() to convert the bound to
> ssizetype has downstream effects in the test suite, in part
> because it seems unexpected for the function to return a signed
> type given that the result cannot be negative, and in part also
> because I see most callers explicitly convert the result to
> size_type_node.

You have to dig into history youself but yes, it doesn't make much sense.
Possibly to avoid negative values to overflow to large positive ones?

Richard.

> Thanks
> Martin