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Migrate away from nonfunctional fenv stubs
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Changes on the directly changed functions: The wins on the rounding functions are pretty significant. Looks like LLVM is having a slightly harder time optimizing sqrt and fma. |
Many routines have some form of handling for rounding mode and floating point exceptions, which are implemented via a combination of stubs and `force_eval!` use. This is suboptimal, however, because: 1. Rust does not interact with the floating point environment, so most of this code does nothing. 2. The parts of the code that are not dead are not testable. 3. `force_eval!` blocks optimizations, which is unnecessary because we do not rely on its side effects. We cannot ensure correct rounding and exception handling in all cases without some form of arithmetic operations that are aware of this behavior. However, the cases where rounding mode is explicitly handled or exceptions are explicitly raised are testable. Make this possible here for functions that depend on `math::fenv` by moving the implementation to a nonpublic function that takes a `Round` and returns a `Status`. Link: https://github.com/rust-lang/libm/issues/480
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Migrate away from nonfunctional `fenv` stubs
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Many routines have some form of handling for rounding mode and floating point exceptions, which are implemented via a combination of stubs and
force_eval!use. This is suboptimal, however, because:force_eval!blocks optimizations, which is unnecessary because we do not rely on its side effects.We cannot ensure correct rounding and exception handling in all cases without some form of arithmetic operations that are aware of this behavior. However, the cases where rounding mode is explicitly handled or exceptions are explicitly raised are testable. Make this possible here for functions that depend on
math::fenvby moving the implementation to a nonpublic function that takes aRoundand returns aStatus.Cc: rust-lang/compiler-builtins#842