r221064 - Avoid undefined behavior in the x86 lzcnt header file by explicitly checking for 0 before calling __builtin_clz. Without this the optimizers may take advantage of the undefined behavior and produce incorrect results. LLVM itself still needs

[Craig Topper]

Fixed bmiintrin.h in r221065. Thanks for pointing it out. I also added the
Intel documented names for these intrinsics in r221066.

On Sat, Nov 1, 2014 at 3:47 PM, Robinson, Paul <
Paul_Robinson at playstation.sony.com> wrote:

> Thanks.  I've been trying to do this today but having trouble getting to
> my work systems from home.
>
> Are there __builtin_ctz* calls (in bmiintrin.h or whatever) that assume
> they
> have tzcnt, and are also missing guards?
> --paulr
>
> > -----Original Message-----
> > From: cfe-commits-bounces at cs.uiuc.edu [mailto:cfe-commits-
> > bounces at cs.uiuc.edu] On Behalf Of Craig Topper
> > Sent: Saturday, November 01, 2014 3:25 PM
> > To: cfe-commits at cs.uiuc.edu
> > Subject: r221064 - Avoid undefined behavior in the x86 lzcnt header file
> > by explicitly checking for 0 before calling __builtin_clz. Without this
> > the optimizers may take advantage of the undefined behavior and produce
> > incorrect results. LLVM itself still needs t...
> >
> > Author: ctopper
> > Date: Sat Nov  1 17:25:23 2014
> > New Revision: 221064
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=221064&view=rev
> > Log:
> > Avoid undefined behavior in the x86 lzcnt header file by explicitly
> > checking for 0 before calling __builtin_clz. Without this the optimizers
> > may take advantage of the undefined behavior and produce incorrect
> > results. LLVM itself still needs to be taught to merge the zero check
> into
> > the llvm.ctlz with defined zero behavior.
> >
> > Modified:
> >     cfe/trunk/lib/Headers/lzcntintrin.h
> >
> > Modified: cfe/trunk/lib/Headers/lzcntintrin.h
> > URL: http://llvm.org/viewvc/llvm-
> >
> project/cfe/trunk/lib/Headers/lzcntintrin.h?rev=221064&r1=221063&r2=221064
> > &view=diff
> >
> ==========================================================================
> > ====
> > --- cfe/trunk/lib/Headers/lzcntintrin.h (original)
> > +++ cfe/trunk/lib/Headers/lzcntintrin.h Sat Nov  1 17:25:23 2014
> > @@ -35,20 +35,20 @@
> >  static __inline__ unsigned short __attribute__((__always_inline__,
> > __nodebug__))
> >  __lzcnt16(unsigned short __X)
> >  {
> > -  return __builtin_clzs(__X);
> > +  return __X ? __builtin_clzs(__X) : 16;
> >  }
> >
> >  static __inline__ unsigned int __attribute__((__always_inline__,
> > __nodebug__))
> >  __lzcnt32(unsigned int __X)
> >  {
> > -  return __builtin_clz(__X);
> > +  return __X ? __builtin_clz(__X) : 32;
> >  }
> >
> >  #ifdef __x86_64__
> >  static __inline__ unsigned long long __attribute__((__always_inline__,
> > __nodebug__))
> >  __lzcnt64(unsigned long long __X)
> >  {
> > -  return __builtin_clzll(__X);
> > +  return __X ? __builtin_clzll(__X) : 64;
> >  }
> >  #endif
> >
> >
> >
> > _______________________________________________
> > cfe-commits mailing list
> > cfe-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>



-- 
~Craig
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