WIP.

Cargo.toml

@@ -14,3 +14,4 @@ structopt = "0.3"
 log = "0.4"
 env_logger = "0.9"
 fxhash = "0.2"
+smallvec = "1.7"

src/backend.rs

@@ -1,54 +1,37 @@
 //! IR-to-Wasm transform.
 
-use crate::ir::*;
-use fxhash::{FxHashMap, FxHashSet};
+use crate::{cfg::CFGInfo, ir::*};
 
-pub fn treeify_function(func: &mut FunctionBody) -> FxHashSet<(BlockId, InstId)> {
-    // First, count uses of all values.
-    let mut uses: FxHashMap<(BlockId, InstId, usize), usize> = FxHashMap::default();
-    for block in &func.blocks {
-        for inst in &block.insts {
-            for input in &inst.inputs {
-                match input {
-                    &Operand::Value(value_id) => {
-                        if let ValueKind::Inst(src_block, src_inst, idx) =
-                            &func.values[value_id].kind
-                        {
-                            *uses.entry((*src_block, *src_inst, *idx)).or_insert(0) += 1;
-                        }
-                    }
-                    _ => {}
-                }
-            }
-        }
-
-        for arg in block.terminator.args() {
-            match arg {
-                Operand::Value(value_id) => {
-                    if let ValueKind::Inst(src_block, src_inst, idx) = &func.values[value_id].kind {
-                        *uses.entry((*src_block, *src_inst, *idx)).or_insert(0) += 1;
-                    }
-                }
-                _ => {}
-            }
-        }
-    }
-
-    // Next, treeify all insts with only one use.
-    let mut single_use_insts: FxHashSet<(BlockId, InstId)> = FxHashSet::default();
-    for (block_idx, block) in func.blocks.iter().enumerate() {
-        for (inst_idx, inst) in block.insts.iter().enumerate() {
-            let all_one_use = (0..inst.outputs.len()).all(|output| {
-                uses.get(&(block_idx, inst_idx, output))
-                    .cloned()
-                    .unwrap_or(0)
-                    <= 1
-            });
-            if all_one_use {
-                single_use_insts.insert((block_idx, inst_idx));
-            }
-        }
-    }
-    
-    single_use_insts
+#[derive(Clone, Debug)]
+pub enum Shape {
+    Block { head: BlockId, children: Vec<Shape> },
+    Loop { head: BlockId, children: Vec<Shape> },
+    Leaf { block: BlockId, succs: Vec<BlockId> },
+}
+
+enum Region {
+    /// Forward-branch region. Extends from end (just prior to
+    /// terminator) of first block to just before second block. Can be
+    /// extended earlier, prior to the beginning, if needed.
+    Forward(BlockId, BlockId),
+
+    /// Backward-branch region. Extends from start of first block to
+    /// end (after terminator) of second block. Can be extended past
+    /// the end if needed. TODO: actually record all jump-points.
+    Backward(BlockId, BlockId),
+}
+
+impl Shape {
+    pub fn compute(f: &FunctionBody, cfg: &CFGInfo) -> Self {
+        // Process all non-contiguous edges in RPO block order. For
+        // forward and backward edges, emit Regions.
+
+        // Sort regions by start. Then examine adjacent regions to
+        // resolve nesting. If out-of-order, we can extend a Forward
+        // region's start backward, or a Backward region's end
+        // forward. If still out-of-order, drop any conflicting
+        // Backward; we'll handle by duplication.
+
+        todo!()
+    }
 }

src/cfg/domtree.rs

@@ -0,0 +1,118 @@
+/*
+ * Derives from the dominator tree implementation in regalloc.rs, which is
+ * licensed under the Apache Public License 2.0 with LLVM Exception. See:
+ * https://github.com/bytecodealliance/regalloc.rs
+ */
+
+// This is an implementation of the algorithm described in
+//
+//   A Simple, Fast Dominance Algorithm
+//   Keith D. Cooper, Timothy J. Harvey, and Ken Kennedy
+//   Department of Computer Science, Rice University, Houston, Texas, USA
+//   TR-06-33870
+//   https://www.cs.rice.edu/~keith/EMBED/dom.pdf
+
+use crate::ir::{BlockId, INVALID_BLOCK};
+
+// Helper
+fn merge_sets(
+    idom: &[BlockId], // map from BlockId to BlockId
+    block_to_rpo: &[Option<u32>],
+    mut node1: BlockId,
+    mut node2: BlockId,
+) -> BlockId {
+    while node1 != node2 {
+        if node1 == INVALID_BLOCK || node2 == INVALID_BLOCK {
+            return INVALID_BLOCK;
+        }
+        let rpo1 = block_to_rpo[node1].unwrap();
+        let rpo2 = block_to_rpo[node2].unwrap();
+        if rpo1 > rpo2 {
+            node1 = idom[node1];
+        } else if rpo2 > rpo1 {
+            node2 = idom[node2];
+        }
+    }
+    assert!(node1 == node2);
+    node1
+}
+
+pub fn calculate<'a, PredFn: Fn(BlockId) -> &'a [BlockId]>(
+    num_blocks: usize,
+    preds: PredFn,
+    post_ord: &[BlockId],
+    start: BlockId,
+) -> Vec<BlockId> {
+    // We have post_ord, which is the postorder sequence.
+
+    // Compute maps from RPO to block number and vice-versa.
+    let mut block_to_rpo = vec![None; num_blocks];
+    block_to_rpo.resize(num_blocks, None);
+    for (i, rpo_block) in post_ord.iter().rev().enumerate() {
+        block_to_rpo[*rpo_block] = Some(i as u32);
+    }
+
+    let mut idom = vec![INVALID_BLOCK; num_blocks];
+
+    // The start node must have itself as a parent.
+    idom[start] = start;
+
+    let mut changed = true;
+    while changed {
+        changed = false;
+        // Consider blocks in reverse postorder. Skip any that are unreachable.
+        for &node in post_ord.iter().rev() {
+            let rponum = block_to_rpo[node].unwrap();
+
+            let mut parent = INVALID_BLOCK;
+            for &pred in preds(node).iter() {
+                let pred_rpo = match block_to_rpo[pred] {
+                    Some(r) => r,
+                    None => {
+                        // Skip unreachable preds.
+                        continue;
+                    }
+                };
+                if pred_rpo < rponum {
+                    parent = pred;
+                    break;
+                }
+            }
+
+            if parent != INVALID_BLOCK {
+                for &pred in preds(node).iter() {
+                    if pred == parent {
+                        continue;
+                    }
+                    if idom[pred] == INVALID_BLOCK {
+                        continue;
+                    }
+                    parent = merge_sets(&idom, &block_to_rpo[..], parent, pred);
+                }
+            }
+
+            if parent != INVALID_BLOCK && parent != idom[node] {
+                idom[node] = parent;
+                changed = true;
+            }
+        }
+    }
+
+    // Now set the start node's dominator-tree parent to "invalid";
+    // this allows the loop in `dominates` to terminate.
+    idom[start] = INVALID_BLOCK;
+
+    idom
+}
+
+pub fn dominates(idom: &[BlockId], a: BlockId, mut b: BlockId) -> bool {
+    loop {
+        if a == b {
+            return true;
+        }
+        if b == INVALID_BLOCK {
+            return false;
+        }
+        b = idom[b];
+    }
+}

src/cfg/mod.rs

@@ -0,0 +1,91 @@
+//! Lightweight CFG analyses.
+
+// Borrowed from regalloc2's cfg.rs, which is also Apache-2.0 with
+// LLVM exception.
+
+use crate::ir::{BlockId, FunctionBody, Terminator};
+use smallvec::SmallVec;
+
+pub mod domtree;
+pub mod postorder;
+
+#[derive(Clone, Debug)]
+pub struct CFGInfo {
+    /// Predecessors for each block.
+    pub block_preds: Vec</* BlockId, */ SmallVec<[BlockId; 4]>>,
+    /// Successors for each block.
+    pub block_succs: Vec</* BlockId, */ SmallVec<[BlockId; 4]>>,
+    /// Blocks that end in return.
+    pub return_blocks: Vec<BlockId>,
+    /// Postorder traversal of blocks.
+    pub postorder: Vec<BlockId>,
+    /// Position of each block in postorder, if reachable.
+    pub postorder_pos: Vec</* BlockId, */ Option<usize>>,
+    /// Domtree parents, indexed by block.
+    pub domtree: Vec<BlockId>,
+}
+
+impl CFGInfo {
+    pub fn new(f: &FunctionBody) -> CFGInfo {
+        let mut block_preds = vec![SmallVec::new(); f.blocks.len()];
+        let mut block_succs = vec![SmallVec::new(); f.blocks.len()];
+        for block in 0..f.blocks.len() {
+            for succ in f.blocks[block].successors() {
+                block_preds[succ].push(block);
+                block_succs[block].push(succ);
+            }
+        }
+
+        let mut return_blocks = vec![];
+        for block in 0..f.blocks.len() {
+            if let Terminator::Return { .. } = &f.blocks[block].terminator {
+                return_blocks.push(block);
+            }
+        }
+
+        let postorder = postorder::calculate(f.blocks.len(), 0, |block| &block_succs[block]);
+
+        let mut postorder_pos = vec![None; f.blocks.len()];
+        for (i, block) in postorder.iter().enumerate() {
+            postorder_pos[*block] = Some(i);
+        }
+
+        let domtree = domtree::calculate(
+            f.blocks.len(),
+            |block| &&block_preds[block],
+            &postorder[..],
+            0,
+        );
+
+        CFGInfo {
+            block_preds,
+            block_succs,
+            return_blocks,
+            postorder,
+            postorder_pos,
+            domtree,
+        }
+    }
+
+    pub fn dominates(&self, a: BlockId, b: BlockId) -> bool {
+        domtree::dominates(&self.domtree[..], a, b)
+    }
+
+    pub fn succs(&self, block: BlockId) -> &[BlockId] {
+        &self.block_succs[block]
+    }
+
+    pub fn preds(&self, block: BlockId) -> &[BlockId] {
+        &self.block_preds[block]
+    }
+
+    pub fn pred_count_with_entry(&self, block: BlockId) -> usize {
+        let is_entry = block == 0;
+        self.preds(block).len() + if is_entry { 1 } else { 0 }
+    }
+
+    pub fn succ_count_with_return(&self, block: BlockId) -> usize {
+        let is_return = self.return_blocks.binary_search(&block).is_ok();
+        self.succs(block).len() + if is_return { 1 } else { 0 }
+    }
+}

src/cfg/postorder.rs

@@ -0,0 +1,54 @@
+//! Fast postorder computation.
+
+// Borrowed from regalloc2's postorder.rs, which is also Apache-2.0
+// with LLVM-exception.
+
+use crate::ir::BlockId;
+use smallvec::{smallvec, SmallVec};
+
+pub fn calculate<'a, SuccFn: Fn(BlockId) -> &'a [BlockId]>(
+    num_blocks: usize,
+    entry: BlockId,
+    succ_blocks: SuccFn,
+) -> Vec<BlockId> {
+    let mut ret = vec![];
+
+    // State: visited-block map, and explicit DFS stack.
+    let mut visited = vec![];
+    visited.resize(num_blocks, false);
+
+    struct State<'a> {
+        block: BlockId,
+        succs: &'a [BlockId],
+        next_succ: usize,
+    }
+    let mut stack: SmallVec<[State; 64]> = smallvec![];
+
+    visited[entry] = true;
+    stack.push(State {
+        block: entry,
+        succs: succ_blocks(entry),
+        next_succ: 0,
+    });
+
+    while let Some(ref mut state) = stack.last_mut() {
+        // Perform one action: push to new succ, skip an already-visited succ, or pop.
+        if state.next_succ < state.succs.len() {
+            let succ = state.succs[state.next_succ];
+            state.next_succ += 1;
+            if !visited[succ] {
+                visited[succ] = true;
+                stack.push(State {
+                    block: succ,
+                    succs: succ_blocks(succ),
+                    next_succ: 0,
+                });
+            }
+        } else {
+            ret.push(state.block);
+            stack.pop();
+        }
+    }
+
+    ret
+}

src/frontend.rs

@@ -2,6 +2,23 @@
 
 #![allow(dead_code)]
 
+/*
+
+- TODO: better local-variable handling:
+  - pre-pass to scan for locations of definitions of all locals. for
+    each frame, record set of vars that are def'd.
+  - during main pass:
+    - for an if/else, add blockparams to join block for all vars def'd
+      in either side.
+    - for a block, add blockparams to out-block for all vars def'd in
+      body of block.
+    - for a loop, add blockparams to header block for all vars def'd
+      in body.
+    - when generating a branch to any block, just emit current values
+      for every local in blockparams.
+
+ */
+
 use crate::ir::*;
 use crate::op_traits::{op_inputs, op_outputs};
 use anyhow::{bail, Result};
@@ -130,7 +147,6 @@ fn parse_body<'a, 'b>(
         builder.body.values.push(ValueDef {
             kind: ValueKind::Arg(arg_idx),
             ty: arg_ty,
-            local: Some(local_idx),
         });
         trace!("defining local {} to value {}", local_idx, value);
         builder.locals.insert(local_idx, (arg_ty, value));
@@ -315,7 +331,6 @@ impl<'a, 'b> FunctionBodyBuilder<'a, 'b> {
                             self.body.values.push(ValueDef {
                                 ty,
                                 kind: ValueKind::Inst(block, inst, 0),
-                                local: Some(*local_index),
                             });
                             value
                         } else {
@@ -888,7 +903,6 @@ impl<'a, 'b> FunctionBodyBuilder<'a, 'b> {
             self.body.values.push(ValueDef {
                 kind: ValueKind::BlockParam(block, block_param_num),
                 ty,
-                local: None,
             });
             self.op_stack.push((ty, value_id));
             block_param_num += 1;
@@ -903,7 +917,6 @@ impl<'a, 'b> FunctionBodyBuilder<'a, 'b> {
                 self.body.values.push(ValueDef {
                     kind: ValueKind::BlockParam(block, block_param_num),
                     ty,
-                    local: Some(local_id),
                 });
                 block_param_num += 1;
                 self.locals.insert(local_id, (ty, value_id));
@@ -939,7 +952,6 @@ impl<'a, 'b> FunctionBodyBuilder<'a, 'b> {
                 self.body.values.push(ValueDef {
                     kind: ValueKind::Inst(block, inst, i),
                     ty: output_ty,
-                    local: None,
                 });
                 self.op_stack.push((output_ty, val));
             }

src/ir.rs

@@ -12,6 +12,7 @@ pub type ValueId = usize;
 pub type LocalId = u32;
 
 pub const NO_VALUE: ValueId = usize::MAX;
+pub const INVALID_BLOCK: BlockId = usize::MAX;
 
 #[derive(Clone, Debug, Default)]
 pub struct Module<'a> {
@@ -48,7 +49,6 @@ pub struct FunctionBody<'a> {
 pub struct ValueDef {
     pub kind: ValueKind,
     pub ty: Type,
-    pub local: Option<LocalId>,
 }
 
 #[derive(Clone, Debug)]
@@ -65,6 +65,55 @@ pub struct Block<'a> {
     pub terminator: Terminator,
 }
 
+impl<'a> Block<'a> {
+    pub fn successors(&self) -> Vec<BlockId> {
+        self.terminator.successors()
+    }
+
+    pub fn values<'b>(&'b self) -> impl Iterator<Item = ValueId> + 'b {
+        self.insts
+            .iter()
+            .map(|inst| inst.outputs.iter().cloned())
+            .flatten()
+    }
+
+    pub fn visit_operands<F: Fn(&Operand)>(&self, f: F) {
+        for inst in &self.insts {
+            for input in &inst.inputs {
+                f(input);
+            }
+        }
+        match &self.terminator {
+            &Terminator::CondBr { ref cond, .. } => f(cond),
+            &Terminator::Select { ref value, .. } => f(value),
+            &Terminator::Return { ref values, .. } => {
+                for value in values {
+                    f(value);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    pub fn update_operands<F: Fn(&mut Operand)>(&mut self, f: F) {
+        for inst in &mut self.insts {
+            for input in &mut inst.inputs {
+                f(input);
+            }
+        }
+        match &mut self.terminator {
+            &mut Terminator::CondBr { ref mut cond, .. } => f(cond),
+            &mut Terminator::Select { ref mut value, .. } => f(value),
+            &mut Terminator::Return { ref mut values, .. } => {
+                for value in values {
+                    f(value);
+                }
+            }
+            _ => {}
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct Inst<'a> {
     pub operator: Operator<'a>,
@@ -163,14 +212,6 @@ impl<'a> Module<'a> {
 
     pub fn to_wasm_bytes(mut self) -> Vec<u8> {
         // TODO
-        for func in &mut self.funcs {
-            match func {
-                &mut FuncDecl::Body(_, ref mut body) => {
-                    let _deleted_insts = backend::treeify_function(body);
-                }
-                _ => {}
-            }
-        }
         self.orig_bytes.to_vec()
     }
 }

src/lib.rs

@@ -12,5 +12,6 @@ mod dataflow;
 mod frontend;
 mod ir;
 mod op_traits;
+mod cfg;
 
 pub use ir::*;