[LLVMdev] unrecognized command line option "-Wno-long-double"

Dale Johannesen dalej at apple.com
Thu Jun 5 13:27:44 CDT 2008


On Jun 5, 2008, at 4:33 AM, Duncan Sands wrote:

> Hi Filipe,
>
>> LLVM-gcc can't recognize this option, don't know why, because the gcc
>> in Mac OS X (quite old, compared to 4.2) can recognize it.
>
> mainline gcc-4.2 doesn't recognize this option as far as I can see.   
> Since
> llvm-gcc is based on gcc-4.2, it has inherited this behaviour from it.

Not exactly.  -Wno-long-double was always an Apple thing, not in FSF.   
Here is the history:

In the earliest Apple releases of gcc (around 2000) long double was  
implemented the same as double, which is C standard conformant but not  
very useful; however, it was always planned to implement "real" long  
double later.  Thus, those releases warned about any use of long  
double:  "size may change in a future release".  As always with  
warnings, somebody wanted a way to turn it off, and -Wno-long-double  
was added to do so.  In due course the size of long double was  
incompatibly changed, removing the need for the warning:  the current  
gcc-4.0 does not warn on long double, but continues to accept the  
flag, which doesn't do anything.  Going forward, gcc-4.2 will remove  
the flag as well, and llvm-gcc-4.2 is already there.

So the best thing is not to use it.  There is no reason to.



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