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14e6d05dfb
Currently our implementations for `abs` and `copysign` are defined on the trait, and these are then called from `generic`. It would be better to call core's `.abs()` / `.copysign(y)`, but we can't do this in the generic because calling the standalone function could become recursive (`fabsf` becomes `intrinsics::fabsf32`, that may lower to a call to `fabsf`). Change this so the traits uses the call to `core` if available, falling back to a call to the standalone generic function. In practice the recursion isn't likely to be a problem since LLVM probably always lowers `abs`/`copysign` to assembly, but this pattern should be more correct for functions that we will add in the future (e.g. `fma`). This should eventually be followed by a change to call the trait methods rather than `fabs`/`copysign` directly.