On Mon, 12 Jun 2017, Tamar Christina wrote: > x * copysign (1.0, y) and > x * copysign (-1.0, y) > > to: > > x ^ (y & (1 << sign_bit_position))
Note that this needs to be disabled for -fsignaling-nans, as if x is a signaling NaN, the multiplication converts it to a quiet NaN and raises "invalid". > This is done by creating a special builtin during matching and generate the > appropriate instructions during expand. This new builtin is called XORSIGN. If the built-in function has a user-visible name such as __builtin_xorsign (as opposed to one that's not a C identifier), it needs to be documented as a user-visible feature. I'd suggest not having such a user-visible built-in function. -- Joseph S. Myers jos...@codesourcery.com
