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

[Quentin Colombet via llvm-dev]

Good point, I forgot to check the standard.
Given the clang was failing I assumed the code was wrong x).

I am guessing there is something weird with the project, because indeed, paragraph 7.2 of the standard says:
The assert macro is redefined according to the current state of NDEBUG each time that

<assert.h> is included. 


> On Oct 4, 2017, at 2:53 PM, Craig Topper <craig.topper at gmail.com> wrote:
> 
> 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 <mailto: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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