machinst: allow passing constant information to the instruction emitter;

A new associated type Info is added to MachInstEmit, which is the
immutable counterpart to State. It can't easily be constructed from an
ABICallee, since it would require adding an associated type to the
latter, and making so leaks the associated type in a lot of places in
the code base and makes the code harder to read. Instead, the EmitInfo
state can simply be passed to the `Vcode::emit` function directly.

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

@@ -3,6 +3,7 @@
 
 use crate::binemit::{CodeOffset, StackMap};
 use crate::ir::{types, ExternalName, Opcode, SourceLoc, TrapCode, Type};
+use crate::isa::x64::settings as x64_settings;
 use crate::machinst::*;
 use crate::{settings, settings::Flags, CodegenError, CodegenResult};
 use alloc::boxed::Box;
@@ -2559,11 +2560,30 @@ pub struct EmitState {
     stack_map: Option<StackMap>,
 }
 
+/// Constant state used during emissions of a sequence of instructions.
+pub struct EmitInfo {
+    flags: settings::Flags,
+    isa_flags: x64_settings::Flags,
+}
+
+impl EmitInfo {
+    pub(crate) fn new(flags: settings::Flags, isa_flags: x64_settings::Flags) -> Self {
+        Self { flags, isa_flags }
+    }
+}
+
+impl MachInstEmitInfo for EmitInfo {
+    fn flags(&self) -> &Flags {
+        &self.flags
+    }
+}
+
 impl MachInstEmit for Inst {
     type State = EmitState;
+    type Info = EmitInfo;
 
-    fn emit(&self, sink: &mut MachBuffer<Inst>, flags: &settings::Flags, state: &mut Self::State) {
-        emit::emit(self, sink, flags, state);
+    fn emit(&self, sink: &mut MachBuffer<Inst>, info: &Self::Info, state: &mut Self::State) {
+        emit::emit(self, sink, info, state);
     }
 
     fn pretty_print(&self, mb_rru: Option<&RealRegUniverse>, _: &mut Self::State) -> String {