Optimize based on possible enum class values?

Mikhail Maltsev maltsevm@gmail.com
Thu May 19 10:03:00 GMT 2016


On 05/19/2016 04:37 AM, ☂Josh Chia (谢任中) wrote:
> Is there a way to tell gcc to assume that the underlying integer value
> is for a valid enum value and optimize accordingly? Even more
> generally, is there a way to give optimization hints to the compiler
> that a variable can only have certain values at a certain point in the
> code?
> 
You can use this idiom to tell GCC that 'condition' is true:

if (!condition)
  __builtin_unreachable();

GCC is able to infer value ranges from conditions like e.g. (x >= a && x <= b).

-- 
Regards,
    Mikhail Maltsev



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