https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90248
Alexander Cherepanov <ch3root at openwall dot com> changed:
What |Removed |Added
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CC| |ch3root at openwall dot com
--- Comment #13 from Alexander Cherepanov <ch3root at openwall dot com> ---
(In reply to Andrew Pinski from comment #7)
> I copied an optimization from LLVM so I
> think they also mess up a similar way (though differently).
I looked into reporting this problem to llvm but I don't see it there. In the
current llvm sources I can only find this:
https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp#L2348
// If needed, negate the value that will be the sign argument of the
copysign:
// (bitcast X) < 0 ? -TC : TC --> copysign(TC, X)
// (bitcast X) < 0 ? TC : -TC --> copysign(TC, -X)
// (bitcast X) >= 0 ? -TC : TC --> copysign(TC, -X)
// (bitcast X) >= 0 ? TC : -TC --> copysign(TC, X)
AIUI `bitcast` here means a bitcast to an integer type. For example, this:
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union u { double d; long l; };
double f(double x)
{
return (union u){x}.l >= 0 ? 2.3 : -2.3;
}
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is optimized into this:
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; Function Attrs: nounwind readnone uwtable
define dso_local double @f(double %0) local_unnamed_addr #0 {
%2 = tail call double @llvm.copysign.f64(double 2.300000e+00, double %0)
ret double %2
}
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Did I miss something?
