x64: Migrate {s,u}{div,rem} to ISLE (#6008)

* x64: Add precise-output tests for div traps

This adds a suite of `*.clif` files which are intended to test the
`avoid_div_traps=true` compilation of the `{s,u}{div,rem}` instructions.

* x64: Remove conditional regalloc in `Div` instruction

Move the 8-bit `Div` logic into a dedicated `Div8` instruction to avoid
having conditionally-used registers with respect to regalloc.

* x64: Migrate non-trapping, `udiv`/`urem` to ISLE

* x64: Port checked `udiv` to ISLE

* x64: Migrate urem entirely to ISLE

* x64: Use `test` instead of `cmp` to compare-to-zero

* x64: Port `sdiv` lowering to ISLE

* x64: Port `srem` lowering to ISLE

* Tidy up regalloc behavior and fix tests

* Update docs and winch

* Review comments

* Reword again

* More refactoring test fixes

* More test fixes

cranelift/codegen/src/isa/x64/inst/args.rs

@@ -12,6 +12,8 @@ use smallvec::{smallvec, SmallVec};
 use std::fmt;
 use std::string::String;
 
+pub use crate::isa::x64::lower::isle::generated_code::DivSignedness;
+
 /// An extenstion trait for converting `Writable{Xmm,Gpr}` to `Writable<Reg>`.
 pub trait ToWritableReg {
     /// Convert `Writable{Xmm,Gpr}` to `Writable<Reg>`.
@@ -1878,35 +1880,6 @@ impl fmt::Display for ShiftKind {
     }
 }
 
-/// What kind of division or remainder instruction this is?
-#[derive(Clone, Eq, PartialEq)]
-pub enum DivOrRemKind {
-    /// Signed division.
-    SignedDiv,
-    /// Unsigned division.
-    UnsignedDiv,
-    /// Signed remainder.
-    SignedRem,
-    /// Unsigned remainder.
-    UnsignedRem,
-}
-
-impl DivOrRemKind {
-    pub(crate) fn is_signed(&self) -> bool {
-        match self {
-            DivOrRemKind::SignedDiv | DivOrRemKind::SignedRem => true,
-            _ => false,
-        }
-    }
-
-    pub(crate) fn is_div(&self) -> bool {
-        match self {
-            DivOrRemKind::SignedDiv | DivOrRemKind::UnsignedDiv => true,
-            _ => false,
-        }
-    }
-}
-
 /// These indicate condition code tests.  Not all are represented since not all are useful in
 /// compiler-generated code.
 #[derive(Copy, Clone)]