Remove reference to x87 in "known bugs" section and the -msee2 option
In the GHC user's guide 8.10.1 (=".../latest/..." as of writing), and also 8.10.2 in the Section about known GHC bugs (§17.2.1) there is following entry:
On 32-bit x86 platforms when using the native code generator, the -fexcess-precision option is always on. This means that floating-point calculations are non-deterministic, because depending on how the program is compiled (optimisation settings, for example), certain calculations might be done at 80-bit precision instead of the intended 32-bit or 64-bit precision. Floating-point results may differ when optimisation is turned on. In the worst case, referential transparency is violated, because for example let x = E1 in E2 can evaluate to a different value than E2[E1/x].
One workaround is to use the -msse2 option (see Platform-specific Flags), which generates code to use the SSE2 instruction set instead of the x87 instruction set. SSE2 code uses the correct precision for all floating-point operations, and so gives deterministic results. However, note that this only works with processors that support SSE2 (Intel Pentium 4 or AMD Athlon 64 and later), which is why the option is not enabled by default. The libraries that come with GHC are probably built without this option, unless you built GHC yourself.
This seems to be at odds with the release notes of 8.10.1, Section 3.2.2:
(x86) Native code generator support for legacy x87 floating point coprocessor has been removed. From this point forth GHC will only support floating point via SSE2.
Proposed improvements or changes
It feels like at least the second paragraph of the "known bugs" passage is obsolete. Likely the whole, including the first one, thought someone more knowledgable than me should check.