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Re: C++ PATCH to detect narrowing in case values (PR c++/90805)


On 7/3/19 10:13 AM, Marek Polacek wrote:
On Sat, Jun 22, 2019 at 11:28:36PM -0400, Jason Merrill wrote:
On 6/13/19 5:03 PM, Marek Polacek wrote:
Case values are converted constant expressions, so narrowing conversion is not
permitted.  This patch adds detecting narrowing to case_conversion; it's a
handy spot because we have both the value and the (adjusted) type of the
condition.

Is there a reason not to use build_converted_constant_expr?

The function comment says "Note that if TYPE and VALUE are already integral
we don't really do the conversion because the language-independent
warning/optimization code will work better that way" so I avoided adding any
conversions.

What I could do is to, instead of calling check_narrowing, call
build_converted_constant_expr (type, value, tf_warning_or_error);
and not use its result, but I'm not sure what the benefits would be.

I was thinking about using it instead of the current perform_implicit_conversion_flags, so we get the somewhat different constraints on the conversion. And then it becomes simpler to use it unconditionally but throw the result away in the easy case.

Jason


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