CODEWITHSUNDEEP
c++templatesgccclangconstexpr
Tomilov Anatoliy
Tomilov Anatoliy

Reputation: 16711

Benchmarking compile-time properties of a program

What is the best way to evaluate exact minimal value of -fconstexpr-steps= and -ftemplate-depth= parametres required for compilation of a program?

What I do currently is a bisection of a value. But for real-world template-loaded programs it became very long operation, even being logarithmic on upper limit of a value.

There is -v option and -ftime-report, but even their output not gives any desired information about maximum template depth actually used and number of steps actually passed during evaluation of constant expressions.

Upvotes: 12

Views: 160

Answers (1)

TemplateRex
TemplateRex

Reputation: 70516

You could look at how Boost.Hana does its benchmarking. Its benchmark code is written mostly in the form of eRuby templates. The templates are used to generate C++ files which are then compiled while gathering compilation and execution statistics.

Bisection to find the necessary values of -ftemplate-depth and -fconstexpr-steps is of course a bit cumbersome to do by hand, but you could also write a script (Ruby, Python, whatever floats your boat) to automate this. Just double the initial value in a simple while loop until the program compiles successfully.

Upvotes: 3

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