[Cython] OS X 10.7 Lion: GCC __builtin_expect unrecognized inside OpenMP blocks

Lisandro Dalcin dalcinl at gmail.com
Sun Mar 11 09:26:08 CET 2012

On 11 March 2012 09:46, mark florisson <markflorisson88 at gmail.com> wrote:
> On 10 March 2012 14:00, Stefan Behnel <stefan_ml at behnel.de> wrote:
>> Lisandro Dalcin, 10.03.2012 10:51:
>>> On 10 March 2012 03:41, mark florisson wrote:
>>>> On 9 March 2012 14:22, Lisandro Dalcin wrote:
>>>>> I'm basically experiencing the issues here:
>>>>> http://www.cocoabuilder.com/archive/xcode/310299-error-calling-builtin-expect-inside-omp-parallel-for.html
>>>>> Can you imagine any way to workaround it?
>>>> What a lovely C compiler bug... Did you file a bug report with gcc or
>>>> xcode? What version of gcc does Lion ship with?
>>> I'm using a Mac just by accident, no idea (nor motivation) to report
>>> bugs to Apple.
>>> $ gcc --version
>>> i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc.
>>> build 5658) (LLVM build 2336.9.00)
>>> Could that be the the bug is actually in the LLVM backend?
>>>> I suppose the macro would have to be disabled for OS X Lion inside
>>>> parallel sections (there seems to be __APPLE__ and __OSX__, I don't
>>>> know about detecting the OS X version), that's easy to do (undef and
>>>> redefine to no-ops before parallel section and redefine it again after
>>>> the section). I'll try fixing it during the sprints next week.
>>> Perhaps switching to use a "omp_likely"/"omp_unlikely" macros inside
>>> OpenMP blocks would be nicer than defining/undefining?
>> Could that be coded into the macro or would it require to change the
>> generated code? But at least it sounds like it would not impact code in
>> functions that are being called from within the OpenMP blocks, would it?
>> Just the code straight inside the block. A work-around could still have a
>> substantial impact if it requires changes to the generated code.
> Yeah, that's why I suggested the undef/re-def approach around OpenMP
> blocks. It's some code bloat, but only for the C preprocessor, so it
> should be fine.

I still feel bad about this. What about just disabling branch
prediction if OpenMP is ever used? Or perhaps just protect the
definitions of likely/unlikely with some guard, such as users can
disable them using a -D definition?

Lisandro Dalcin
Predio CONICET-Santa Fe
Colectora RN 168 Km 472, Paraje El Pozo
3000 Santa Fe, Argentina
Tel: +54-342-4511594 (ext 1011)
Tel/Fax: +54-342-4511169

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