refactor: use &'static [PReg] instead of Vec<PReg>

Author: JonasKruckenberg

src/checker.rs

@@ -722,7 +722,7 @@ impl<'a, F: Function> Checker<'a, F> {
         bb_in.insert(f.entry_block(), CheckerState::default());
 
         let mut stack_pregs = PRegSet::empty();
-        for &preg in &machine_env.fixed_stack_slots {
+        for &preg in machine_env.fixed_stack_slots {
             stack_pregs.add(preg);
         }
 

src/fastalloc/mod.rs

@@ -245,9 +245,9 @@ impl<'a, F: Function> Env<'a, F> {
     fn new(func: &'a F, env: &'a MachineEnv) -> Self {
         use alloc::vec;
         let mut regs = [
-            env.preferred_regs_by_class[RegClass::Int as usize].clone(),
-            env.preferred_regs_by_class[RegClass::Float as usize].clone(),
-            env.preferred_regs_by_class[RegClass::Vector as usize].clone(),
+            Vec::from(env.preferred_regs_by_class[RegClass::Int as usize]),
+            Vec::from(env.preferred_regs_by_class[RegClass::Float as usize]),
+            Vec::from(env.preferred_regs_by_class[RegClass::Vector as usize]),
         ];
         regs[0].extend(
             env.non_preferred_regs_by_class[RegClass::Int as usize]

src/fastalloc/tests.rs

@@ -143,15 +143,17 @@ impl RealFunction {
 fn mach_env(no_of_regs: usize) -> MachineEnv {
     MachineEnv {
         preferred_regs_by_class: [
-            (0..no_of_regs)
-                .map(|no| PReg::new(no, RegClass::Int))
-                .collect(),
-            vec![],
-            vec![],
+            Vec::leak(
+                (0..no_of_regs)
+                    .map(|no| PReg::new(no, RegClass::Int))
+                    .collect(),
+            ),
+            &[],
+            &[],
         ],
-        non_preferred_regs_by_class: [vec![], vec![], vec![]],
+        non_preferred_regs_by_class: [&[], &[], &[]],
         scratch_by_class: [None, None, None],
-        fixed_stack_slots: vec![],
+        fixed_stack_slots: &[],
     }
 }
 

src/ion/liveranges.rs

@@ -104,7 +104,7 @@ impl<'a, F: Function> Env<'a, F> {
                 is_stack: false,
             },
         );
-        for &preg in &self.env.fixed_stack_slots {
+        for &preg in self.env.fixed_stack_slots {
             self.pregs[preg.index()].is_stack = true;
         }
         for class in 0..self.preferred_victim_by_class.len() {

src/lib.rs

@@ -338,13 +338,13 @@ impl From<&MachineEnv> for PRegSet {
     fn from(env: &MachineEnv) -> Self {
         let mut res = Self::default();
 
-        for class in env.preferred_regs_by_class.iter() {
+        for class in env.preferred_regs_by_class {
             for preg in class {
                 res.add(*preg)
             }
         }
 
-        for class in env.non_preferred_regs_by_class.iter() {
+        for class in env.non_preferred_regs_by_class {
             for preg in class {
                 res.add(*preg)
             }
@@ -1434,6 +1434,12 @@ impl<'a> Iterator for OutputIter<'a> {
 /// are available to allocate and what register may be used as a
 /// scratch register for each class, and some other miscellaneous info
 /// as well.
+///
+/// Note that `MachineEnv` is designed to be a global configuration struct that programs
+/// will have very few of and generally want to keep around for their entire lifetime.
+/// In order to make static initialization easier the registers lists are static slices instead
+/// of `Vec`s. If your use case depends on dynamically creating the registers lists, consider
+/// `[Vec::leak`].
 #[derive(Clone, Debug)]
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
 pub struct MachineEnv {
@@ -1442,7 +1448,7 @@ pub struct MachineEnv {
     ///
     /// If an explicit scratch register is provided in `scratch_by_class` then
     /// it must not appear in this list.
-    pub preferred_regs_by_class: [Vec<PReg>; 3],
+    pub preferred_regs_by_class: [&'static [PReg]; 3],
 
     /// Non-preferred physical registers for each class. These are the
     /// registers that will be allocated if a preferred register is
@@ -1451,7 +1457,7 @@ pub struct MachineEnv {
     ///
     /// If an explicit scratch register is provided in `scratch_by_class` then
     /// it must not appear in this list.
-    pub non_preferred_regs_by_class: [Vec<PReg>; 3],
+    pub non_preferred_regs_by_class: [&'static [PReg]; 3],
 
     /// Optional dedicated scratch register per class. This is needed to perform
     /// moves between registers when cyclic move patterns occur. The
@@ -1476,7 +1482,7 @@ pub struct MachineEnv {
     ///
     /// `PReg`s in this list cannot be used as an allocatable or scratch
     /// register.
-    pub fixed_stack_slots: Vec<PReg>,
+    pub fixed_stack_slots: &'static [PReg],
 }
 
 /// The output of the register allocator.