Benchmarks that access fenv should use the `STDC FENV_ACCESS` pragma - Githubissues

delcypher / fp-benchmarks-imperial

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Benchmarks that access fenv should use the `STDC FENV_ACCESS` pragma #17

Open delcypher opened 7 years ago

delcypher commented 7 years ago

Several benchmarks

synthetic/fadd_to_exact_zero/fadd_to_exact_zero.c
synthetic/fsub_to_exact_zero/fsub_to_exact_zero.c
synthetic/interval/interval.c
synthetic/rounding_sqrt/rounding_sqrt.c

maybe parts of gsl too (I'm not sure).

access the floating point environment without setting the pragma. This is undefined behaviour and should be fixed.

#pragma STDC FENV_ACCESS ON

Indeed Clang 3.9 at -O3 mis-compiles the interval benchmark.

See https://bugs.llvm.org//show_bug.cgi?id=8100

Note Clang doesn't support this pragma currently.

GCC also miscompiles this benchmark at -O3.

delcypher commented 7 years ago

I've partially fixed this by adding the pragma dfb358710feddd58fd0751c1862a3cc9511a23a2 but Clang doesn't support the pragma and still miscompiles this benchmark.