Retaining asserts' hints under --opt=disable-assertions?

[ecatc...@unit2games.com]

Hi,

I use asserts to a) guarantee compliance (eg preconditions), and b) hint to the compiler about constraints it can take advantage of.

A contrived example:

https://godbolt.org/z/fb5x8s

unmasked uniform int Total(uniform int numbers[], uniform int count)

{

    assert(count==32);

    int total = 0;

    foreach(i = 0...count)

    {

        total += numbers[i];

    }

    return reduce_add(total);

}

The assert for count==32 allows the compiler to generate much leaner code for the loop. If I compile with --opt=disable-assertions for an optimized release build, the code gen becomes worse.

I think there are two parts to this:

1) It seems counter-intuitive that the constraints introduced by asserts are being removed. The reason I would disable asserts is to remove the runtime checks, failure path and associated string constants. It would be an unusual use-case to want to disable them in-order to allow non-compliant data to be used, thus requiring the less optimal code-gen.

2) Is there a reliable alternative to assert() that could apply hints to the compiler instead? I know that there are tricks where you can add mutating no-op statements like count=32; (https://godbolt.org/z/9411vc) but sometimes the constraint is trickier to express than that (eg enforce a pointer is not-null), or the data is const and can't be no-op mutated. For these, assert is quite convenient.

[Dmitry Babokin]

Hi,

This issue has been sitting in my personal to-do list for quite long. We can do so many performance hints with asserts, likely and unlikely hints and it would be good not to have them as runtime checks.

I think right now we don't have a mechanism to have a workaround for that.

Could you please file an issue, so we don't miss it for the next release?

Dmitry.

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[Edward Catchpole]

Thank you Dmitry - I'll transfer this to an issue.