[FR] No bounds checks when NDEBUG flag is set

[SteveBronder]

Description

From #853 in stanc3 we recently reverted a check where the compiler actually avoided bounds checks on single indexing functions. This can have a pretty bad performance hit so I think now would be a good time to do something like #2255 where when NDEBUG is set bounds checks are a no-op. This is a standard no debug flag in C++ and is used by boost, eigen, and the standard library to turn off bounds checking. So I think its reasonable that if a user has it set they expect to not have these checks

Example

// in macro.hpp
#ifdefine NDEBUG
#ifndef STAN_NO_RANGE_AND_SIZE_CHECK
#define STAN_NO_RANGE_AND_SIZE_CHECK return
#endif
#else
#ifndef STAN_NO_RANGE_AND_SIZE_CHECK
#define STAN_NO_RANGE_AND_SIZE_CHECK
#endif
#endif

// in check_ranges.hpp
inline void check_range(const char* function, const char* name, int max,
                        int index, int nested_level, const char* error_msg) {
  STAN_NO_RANGE_AND_SIZE_CHECK;
  //... rest of body
}

Expected Output

Bounds checks are not turned on

Current Version:

v4.0.1

[bbbales2]

Closed by #2423

[rok-cesnovar]

@SteveBronder @bbbales2 so I need to set

CXXFLAGS += -DSTAN_NO_RANGE_CHECKS

and that escapes the range and size checks only?

[bbbales2]

I don't think there's a guarantee that we are turning off every range and size check, but we're hopefully turning off enough that it counts performance-wise.

[bbbales2]

And yeah, it's only range and size checks. All value checks should still be there.

[rok-cesnovar]

Cool cool.

I would add a makefile helper so that STAN_NO_RANGE_CHECKS=true adds CXXFLAGS += -DSTAN_NO_RANGE_CHECKS. I hate the CXXFLAGS += syntax :) Alo makes it much easier to add it as a cpp_options.

[bbbales2]

Alo makes it much easier to add it as a cpp_options.

Oh whoops, I thought this was somehow done automagically. I'll add to my list for today and if I don't get to it I'll open an issue for later.

[rok-cesnovar]

Sure thing. For STAN_THREADS for example we do this:

math/make/compiler_flags

Line 282 in 9895be8

ifdef STAN_THREADS