[LLVMdev] Adding Polybench to the test suite

[Gordon Keiser]

> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> On Behalf Of Douglas Teixeira
> Sent: Wednesday, May 30, 2012 4:51 PM
> To: Duncan Sands
> Cc: Tobias Grosser; llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] Adding Polybench to the test suite
> 
> Hi Duncan,
> 
> On Wed, May 30, 2012 at 4:28 PM, Duncan Sands <baldrick at free.fr> wrote:
> > Hi Douglas,
> >
> >> We are trying to add Polybench[1] to the LLVM test suite. So far we
> >> have all but five benchmarks working fine. The problems we're having
> >> in those five benchmarks are due to gcc's versus clang's different
> >> ways to output 'Nan's. We are working to solve this.
> >
> > is it normal (i.e. valid) that they output NaN's differently, or is it
> > a bug?
> >
> 
> We get basically the same output with clang and gcc. The only difference is
> that we get a lot of '-nan's using gcc and we get 'nan's using clang. Tobias sent
> me this earlier today:
> "An implementation may give zero and values that are not floating-point
> numbers (such as  infinities and NaNs) a sign or may
> leave them unsigned. Wherever such values are   unsigned, any
> requirement in this International Standard to retrieve the sign shall produce
> an unspecified sign, and any requirement to set the sign shall be ignored."
> 
> So I don't think it is bug, but we're getting different results, anyway.
> 
> Cheers,
> 
> Douglas
> 

This seems strange.  0 and -0 have different meanings, and an unsigned -0 doesn't make much sense, to me anyway.   

That said, depending on the GCC version I found that it produced strange bugs with 0 and NaN results at anything but -O0, and had to set it to that to match llvm-gcc's (correct) output in the test suites for 2.8 when using GCC 4.2 as the reference.  That might be worth trying.  Oddly the manual for that version claimed that no unsafe floating point optimizations would be enabled at any -O level.    

Cheers,
Gordon

> > Ciao, Duncan.
> >
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