Oops, you're right. https://godbolt.org/z/pAwqUA https://godbolt.org/z/pAwqUA shows it better. Adding a -0 and +0 together in either order gives +0, using the a

Oops, you're right. https://godbolt.org/z/pAwqUA https://godbolt.org/z/pAwqUA shows it better. Adding a -0 and +0 together in either order gives +0, using the actual x86-64 addsd instruction.