On Tue, 12 Sep 2017, Wilco Dijkstra wrote: > * Make -fno-math-errno the default - this mostly affects the code generated > for > sqrt, which should be treated just like floating point division and not set > errno by default (unless you explicitly select C89 mode). > > * Make -fno-trapping-math the default - another obvious one. From the docs:
Note these would both have implications for library math_errhandling settings (since the compiler options can affect built-in functions). In the absence of -ffast-math glibc defines it to (MATH_ERRNO | MATH_ERREXCEPT). __NO_MATH_ERRNO__ exists since GCC 5 to allow it to be defined to just MATH_ERREXCEPT in the -fno-math-errno case, but the header needs updating to respect that. And we don't have a macro for -fno-trapping-math to say whether MATH_ERREXCEPT should be part of the value. My assumption is that with changed defaults glibc would need to compile with -ftrapping-math just as it uses -frounding-math; code may expect transformations that add exceptions not to occur. It probably does not require -fmath-errno (glibc functions do not generally rely on other functions setting errno). -- Joseph S. Myers jos...@codesourcery.com
