WIP.

src/backend/localify.rs

@@ -0,0 +1,258 @@
+//! Localification: a simple form of register allocation that picks
+//! locations for SSA values in Wasm locals.
+
+use crate::backend::treeify::Trees;
+use crate::cfg::CFGInfo;
+use crate::entity::{EntityVec, PerEntity};
+use crate::ir::{Block, FunctionBody, Local, Type, Value, ValueDef};
+use smallvec::{smallvec, SmallVec};
+use std::collections::{HashMap, HashSet};
+
+#[derive(Clone, Debug, Default)]
+pub struct Localifier {
+    values: PerEntity<Value, SmallVec<[Local; 2]>>,
+    locals: EntityVec<Local, Type>,
+}
+
+impl Localifier {
+    pub fn compute(body: &FunctionBody, cfg: &CFGInfo, trees: &Trees) -> Self {
+        Context::new(body, cfg, trees).compute()
+    }
+}
+
+struct Context<'a> {
+    body: &'a FunctionBody,
+    cfg: &'a CFGInfo,
+    trees: &'a Trees,
+    results: Localifier,
+
+    // Affinities (blockparam value to input arg value).
+    affinities: HashMap<Value, SmallVec<[Value; 4]>>,
+
+    // Livein to each block from dominators.
+    livein_values: PerEntity<Block, HashSet<Value>>,
+    livein_locals: PerEntity<Block, HashSet<Local>>,
+}
+
+impl<'a> Context<'a> {
+    fn new(body: &'a FunctionBody, cfg: &'a CFGInfo, trees: &'a Trees) -> Self {
+        let mut results = Localifier::default();
+        // Create locals for function args.
+        for &(ty, value) in &body.blocks[body.entry].params {
+            let param_local = results.locals.push(ty);
+            results.values[value] = smallvec![param_local];
+        }
+        // Compute affinities.
+        let mut affinities = HashMap::default();
+        for block in body.blocks.values() {
+            block.terminator.visit_targets(|target| {
+                for (&arg, &param) in target
+                    .args
+                    .iter()
+                    .zip(body.blocks[target.block].params.iter().map(|(_, val)| val))
+                {
+                    affinities
+                        .entry(param)
+                        .or_insert_with(|| smallvec![])
+                        .push(arg);
+                }
+            });
+        }
+
+        Self {
+            body,
+            cfg,
+            trees,
+            results,
+            affinities,
+            livein_values: PerEntity::default(),
+            livein_locals: PerEntity::default(),
+        }
+    }
+
+    fn compute(mut self) -> Localifier {
+        // Create domtree preorder for traversal (we iterate in
+        // reverse preorder below).
+        let mut order = vec![];
+        order.push(self.body.entry);
+        let mut i = 0;
+        while i < order.len() {
+            for child in self.cfg.dom_children(order[i]) {
+                order.push(child);
+            }
+            i += 1;
+        }
+
+        for &block in order.iter().rev() {
+            self.process(block);
+        }
+
+        debug_assert!(self.livein_values[self.body.entry].is_empty());
+        debug_assert!(self.livein_locals[self.body.entry].is_empty());
+
+        self.results
+    }
+
+    fn process(&mut self, block: Block) {
+        let mut live_values = HashSet::new();
+        let mut live_locals = HashSet::new();
+
+        // Collect liveins of all dominated blocks; this is our initial live-set.
+        for child in self.cfg.dom_children(block) {
+            for &livein_value in &self.livein_values[child] {
+                log::trace!(
+                    "localify: block {} gets livein value {} from block {}",
+                    block,
+                    livein_value,
+                    child
+                );
+                live_values.insert(livein_value);
+            }
+            for &livein_local in &self.livein_locals[child] {
+                live_locals.insert(livein_local);
+            }
+        }
+
+        log::trace!(
+            "localify: process block {}: liveout values {:?} locals {:?}",
+            block,
+            live_values,
+            live_locals
+        );
+
+        // For each use/def in reverse order, update live-set; on last
+        // use (first observed), allocate a local.
+        fn handle_use(
+            body: &FunctionBody,
+            u: Value,
+            live_values: &mut HashSet<Value>,
+            live_locals: &mut HashSet<Local>,
+            results: &mut Localifier,
+            affinities: &HashMap<Value, SmallVec<[Value; 4]>>,
+        ) {
+            let u = body.resolve_alias(u);
+            if live_values.insert(u) {
+                // If there is already an allocation (e.g. for a
+                // function parameter), return.
+                if !results.values[u].is_empty() {
+                    return;
+                }
+
+                // Need to create an allocation.
+                let def = &body.values[u];
+                match def {
+                    &ValueDef::Alias(_value) => {
+                        unreachable!();
+                    }
+                    &ValueDef::PickOutput(value, idx, _) => {
+                        handle_use(body, value, live_values, live_locals, results, affinities);
+                        results.values[u] = smallvec![results.values[value][idx]];
+                    }
+                    &ValueDef::BlockParam(..) | &ValueDef::Operator(..) => {
+                        let locals = def
+                            .tys()
+                            .iter()
+                            .map(|&ty| {
+                                // Try to find a local of the right type that is not live.
+                                let affinities = affinities.get(&u).map(|v| &v[..]).unwrap_or(&[]);
+                                let local = affinities
+                                    .iter()
+                                    .filter_map(|&aff_val| {
+                                        let local = *results.values[aff_val].get(0)?;
+                                        Some((local, results.locals[local]))
+                                    })
+                                    .chain(results.locals.entries().map(|(local, &ty)| (local, ty)))
+                                    .filter_map(|(local, local_ty)| {
+                                        if local_ty == ty && live_locals.insert(local) {
+                                            Some(local)
+                                        } else {
+                                            None
+                                        }
+                                    })
+                                    .next();
+                                local.unwrap_or_else(|| {
+                                    let local = results.locals.push(ty);
+                                    live_locals.insert(local);
+                                    local
+                                })
+                            })
+                            .collect::<SmallVec<_>>();
+                        results.values[u] = locals;
+                    }
+                    &ValueDef::Placeholder(_) | &ValueDef::None => unreachable!(),
+                }
+            }
+        }
+
+        fn handle_def(
+            body: &FunctionBody,
+            d: Value,
+            live_values: &mut HashSet<Value>,
+            live_locals: &mut HashSet<Local>,
+            results: &Localifier,
+        ) {
+            if let ValueDef::Alias(..) = &body.values[d] {
+                return;
+            }
+
+            if live_values.remove(&d) {
+                for &local in &results.values[d] {
+                    live_locals.remove(&local);
+                }
+            }
+        }
+
+        self.body.blocks[block].terminator.visit_uses(|u| {
+            handle_use(
+                self.body,
+                u,
+                &mut live_values,
+                &mut live_locals,
+                &mut self.results,
+                &self.affinities,
+            )
+        });
+
+        for &inst in self.body.blocks[block].insts.iter().rev() {
+            handle_def(
+                self.body,
+                inst,
+                &mut live_values,
+                &mut live_locals,
+                &self.results,
+            );
+            self.body.values[inst].visit_uses(|u| {
+                // If treeified, then don't process use.
+                if !self.trees.owner.contains_key(&u) {
+                    handle_use(
+                        self.body,
+                        u,
+                        &mut live_values,
+                        &mut live_locals,
+                        &mut self.results,
+                        &self.affinities,
+                    )
+                }
+            });
+        }
+
+        for &(_, param) in &self.body.blocks[block].params {
+            handle_def(
+                self.body,
+                param,
+                &mut live_values,
+                &mut live_locals,
+                &self.results,
+            );
+        }
+
+        log::trace!(
+            "localify: process block {}: livein values {:?} locals {:?}",
+            block,
+            live_values,
+            live_locals
+        );
+        self.livein_locals[block] = live_locals;
+        self.livein_values[block] = live_values;
+    }
+}

src/backend/mod.rs

@@ -1,26 +1,28 @@
 //! Backend: IR to Wasm.
 
 use crate::cfg::CFGInfo;
-use crate::entity::{EntityRef, PerEntity};
-use crate::ir::{Block, FunctionBody, Value, ValueDef};
-use crate::passes::rpo::{RPOIndex, RPO};
+use crate::ir::FunctionBody;
+use crate::passes::rpo::RPO;
 use anyhow::Result;
 
 pub mod stackify;
 use stackify::{Context as StackifyContext, WasmBlock};
 pub mod treeify;
 use treeify::Trees;
+pub mod localify;
+use localify::Localifier;
 
 pub struct WasmBackend<'a> {
     body: &'a FunctionBody,
     rpo: RPO,
     trees: Trees,
     ctrl: Vec<WasmBlock<'a>>,
+    locals: Localifier,
 }
 
 impl<'a> WasmBackend<'a> {
     pub fn new(body: &'a FunctionBody) -> Result<WasmBackend<'a>> {
-        log::debug!("Backend compiling:\n{}\n", body.display("| "));
+        log::debug!("Backend compiling:\n{}\n", body.display_verbose("| "));
         let cfg = CFGInfo::new(body);
         let rpo = RPO::compute(body);
         log::debug!("RPO:\n{:?}\n", rpo);
@@ -28,11 +30,14 @@ impl<'a> WasmBackend<'a> {
         log::debug!("Trees:\n{:?}\n", trees);
         let ctrl = StackifyContext::new(body, &cfg, &rpo)?.compute();
         log::debug!("Ctrl:\n{:?}\n", ctrl);
+        let locals = Localifier::compute(body, &cfg, &trees);
+        log::debug!("Locals:\n{:?}\n", locals);
         Ok(WasmBackend {
             body,
             rpo,
             trees,
             ctrl,
+            locals,
         })
     }
 

src/backend/treeify.rs

@@ -28,7 +28,7 @@ impl Trees {
 
         for (value, def) in body.values.entries() {
             match def {
-                &ValueDef::Operator(_, ref args, ref tys) => {
+                &ValueDef::Operator(_, ref args, _) => {
                     // For each of the args, if the value is produced
                     // by a single-output op and is movable, and is
                     // not already recorded in `multi_use`, place it