See this page for details about FPXX:
https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
Using FPXX is the most compatible floating point mode available and
allows the generated code to work in both FR0 and FR1 modes of the
processor. Using MSA (MIPS SIMD) requires FR1, so to use any MSA code we
need a compatible floating point mode.
This commit also sets nooddspreg (disabling the use of odd numbered
single precision float registers) as recommended when enabling FPXX.
Replace all const evaluation with miri
* error reporting in constants prints a stacktrace through all called const fns
* Trivial constant propagation and folding in MIR (always active, irrelevant of the optimization level)
* can now use floating constants in patterns (previously only floating point literals were allowed)
* the future compat lint is still produced for both cases
* can index into constant arrays during const eval (previously feature gated)
* can create a constant union value with field `a` and read from field `b`
* can dereference references into constants
* can create references inside constants (`const X: &u32 = &22`)
* Tuple struct constructors can be used in constants
* regression in const eval errors spans (some of these need improvements in mir debug info)
* can cast floats to ints and vice versa (in constants, and even nan/inf constants)
* Mir dump prints false/true instead of 0u8/1u8
* `1i8 >> [8][0]` does not lint about exceeding bitshifts anymore.
* Needs const propagation across projections
* `foo[I]` produces a const eval lint if `foo: [T; N]` and `N < I`
* Essentially all builtin panics produce lints if they can be statically proven to trigger at runtime. This is on a best effort basis, so there might be some complex cases that don't trigger. (The runtime panic stays there, irrelevant of whether the lint is produced or not)
* can use `union`s to implement `transmute` for `Copy` types in constants without a feature gate. With all the greatness and nasal demons that come with this.
* can convert integers to `&'static T` in constants (useful for embedded)
fixes#34997 (stack overflow with many constants)
fixes#25574 (deref byte strings in patterns)
fixes#27918 (broken mir ICE)
fixes#46114 (ICE on struct constructors in patterns)
fixes#37448 (`SomeStruct { foo } as SomeStruct`)
fixes#43754 (`return` in const fn)
fixes#41898 (tuple struct constructors)
fixes#31364 (infinite recursion with const fn, fixed by miri's recursion limit)
closes#29947 (const indexing stabilization)
fixes#45044 (pattern matching repeat expressions)
fixes#47971 (ICE on const fn + references)
fixes#48081 (ICE on cyclic assoc const error)
fixes#48746 (nonhelpful error message with unions)
r? @eddyb
even though 1k loc are added in tests, this PR reduces the loc in this repository by 700
