forked from OSchip/llvm-project
f5689f8304
widespread glibc bugs. The glibc implementation of exp10 has a very serious precision bug in version 2.15 (and older versions). This is still very widely used (the current Ubuntu LTS for example uses it) and so it isn't reasonable to make transforms that produce these functions. This fixes many miscompiles introduced when we started transforming pow(10.0, ...) into exp10, and it may have fixed other latent miscompiles where exp10 provided sufficient precision but exp10f did not. This is all really horrible. The primary bug has been fixed for over a year and glibc 2.18 works correctly for the test cases I have, but it will be 2017 before the LTS using 2.15 is no longer supported by Ubuntu (and thus reasonable for folks to be relying on). =[ We're either going to need to live without these optimizations, or find a way to switch behavior more dynamically than using simply the fact that the OS is "Linux". To make matters worse, there appears to be significant testing and fixing of numerous other bugs in the exp10 family of functions right now in glibc. While those haven't been causing problems I've seen in the wild, it gives me concerns that we may need to wait until an even later release of glibc before we can reliably transform code into exp10. llvm-svn: 198093 |
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