[llvm-dev] Question: Should we consider valid a variable defined #ifndef NDEBUG scope and used in assert?

[Craig Topper via llvm-dev]

I thought NDEBUG was what the assert macro also used to decide whether to
be an assert or not.

~Craig

On Wed, Oct 4, 2017 at 2:41 PM, Quentin Colombet via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
>
> While audit our code, we found out a strange pattern in one of the LLVM
> headers and we were wondering if that was expected or if it should be fixed.
>
> Namely the problem looks like this:
> #ifndef NDEBUG
>   // Define some variable.
> #endif
>
> assert(/*use this variable, i.e., outside of the ifndef NDEBUG scope*/);
>
> This happens in include/llvm/IR/ValueHandle.h for the variable Poisoned line
> 494
>
> This works because when we build LLVM with assert we explicitly disable
> NDEBUG:
> if( LLVM_ENABLE_ASSERTIONS )
>   […]
>   # On non-Debug builds cmake automatically defines NDEBUG, so we
>   # explicitly undefine it:
>   if( NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
>     add_definitions( -UNDEBUG )
>
> If we use this header in a different project and thus, with potentially
> different rules for macro definitions, the compiler complains with
> error:   use of undeclared identifier ‘Poisoned'
>
> I think the right thing to do is to fix the code to work without the
> special way of setting the macros, but I’d like people opinions first.
>
> Thanks,
> -Quentin
>
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