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

[Quentin Colombet via llvm-dev]

Yep they are messing up with the DEBUG macros…

Sorry for the noise!

> On Oct 4, 2017, at 2:58 PM, Quentin Colombet via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> 
> 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 <mailto: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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> 
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