beta distribution clang M1 optimization short-circuit bug #826
Description
xref scipy/scipy#14901
When built with optimization level >1, Clang on Apple M1 platforms appears to generate incorrect code that does not short-circuit the following if statement from igamma_inverse.hpp:
if((fabs(div) > 1) && (tools::max_value<T>() / fabs(div) < f2))leading to a floating point exception as the right side will overflow if evaluated. This was observed through the Beta distribution with particular ranges of values (see an example below).
Reproducer built with -O2 on M1 Mac with clang:
% clang --version
Apple clang version 14.0.0 (clang-1400.0.29.102)
Target: arm64-apple-darwin21.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
#include <iostream>
#include <cfenv>
#include "boost/math/distributions/beta.hpp"
#pragma STDC FENV_ACCESS ON
int main() {
constexpr double q {0.999995};
constexpr double a {2};
constexpr double b {99999};
std::feclearexcept(FE_ALL_EXCEPT);
boost::math::beta_distribution<double> d {a, b};
const auto ans = boost::math::quantile(d, q);
if(std::fetestexcept(FE_OVERFLOW)) {
std::cout << "overflow reported" << std::endl;
} else {
std::cout << "overflow not reported" << std::endl;
}
std::cout << std::setprecision(16) << "Ans is: " << ans << std::endl;
return 0;
}
// overflow reported
// Ans is: 0.000149761910560502Overflow is not reported when built with -O1 or when building with Mac Intel (or any other platform really).