WIP.

fuzz/Cargo.toml

@@ -26,3 +26,9 @@ name = "parse_ir"
 path = "fuzz_targets/parse_ir.rs"
 test = false
 doc = false
+
+[[bin]]
+name = "roundtrip"
+path = "fuzz_targets/roundtrip.rs"
+test = false
+doc = false

fuzz/fuzz_targets/roundtrip.rs

@@ -0,0 +1,11 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+use waffle::Module;
+
+fuzz_target!(|module: wasm_smith::Module| {
+    let _ = env_logger::try_init();
+    let orig_bytes = module.to_bytes();
+    let parsed_module = Module::from_wasm_bytes(&orig_bytes[..]).unwrap();
+    let _ = parsed_module.to_wasm_bytes();
+});

src/backend.rs

@@ -0,0 +1,54 @@
+//! IR-to-Wasm transform.
+
+use crate::ir::*;
+use fxhash::{FxHashMap, FxHashSet};
+
+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
+}

src/frontend.rs

@@ -14,6 +14,7 @@ use wasmparser::{
 
 pub fn wasm_to_ir(bytes: &[u8]) -> Result<Module<'_>> {
     let mut module = Module::default();
+    module.orig_bytes = bytes;
     let parser = Parser::new(0);
     let mut next_func = 0;
     for payload in parser.parse_all(bytes) {
@@ -770,7 +771,7 @@ impl<'a, 'b> FunctionBodyBuilder<'a, 'b> {
         &self.ctrl_stack[self.ctrl_stack.len() - 1 - relative_depth as usize]
     }
 
-    fn fill_block_params_with_locals(&mut self, target: BlockId, args: &mut Vec<Operand<'a>>) {
+    fn fill_block_params_with_locals(&mut self, target: BlockId, args: &mut Vec<Operand>) {
         if !self.block_param_locals.contains_key(&target) {
             let mut keys: Vec<LocalId> = self.locals.keys().cloned().collect();
             keys.sort();
@@ -789,7 +790,7 @@ impl<'a, 'b> FunctionBodyBuilder<'a, 'b> {
 
     fn emit_branch(&mut self, target: BlockId, args: &[ValueId]) {
         if let Some(block) = self.cur_block {
-            let mut args: Vec<Operand<'a>> = args.iter().map(|&val| Operand::value(val)).collect();
+            let mut args: Vec<Operand> = args.iter().map(|&val| Operand::value(val)).collect();
             self.fill_block_params_with_locals(target, &mut args);
             let target = BlockTarget {
                 block: target,
@@ -840,7 +841,7 @@ impl<'a, 'b> FunctionBodyBuilder<'a, 'b> {
         args: &[ValueId],
     ) {
         if let Some(block) = self.cur_block {
-            let args: Vec<Operand<'a>> = args.iter().map(|&arg| Operand::value(arg)).collect();
+            let args: Vec<Operand> = args.iter().map(|&arg| Operand::value(arg)).collect();
             let targets = indexed_targets
                 .iter()
                 .map(|&block| {

src/ir.rs

@@ -1,6 +1,6 @@
 //! Intermediate representation for Wasm.
 
-use crate::frontend;
+use crate::{backend, frontend};
 use anyhow::Result;
 use wasmparser::{FuncType, Operator, Type};
 
@@ -15,6 +15,7 @@ pub const NO_VALUE: ValueId = usize::MAX;
 
 #[derive(Clone, Debug, Default)]
 pub struct Module<'a> {
+    pub orig_bytes: &'a [u8],
     pub funcs: Vec<FuncDecl<'a>>,
     pub signatures: Vec<FuncType>,
     pub globals: Vec<Type>,
@@ -61,28 +62,26 @@ pub enum ValueKind {
 pub struct Block<'a> {
     pub params: Vec<Type>,
     pub insts: Vec<Inst<'a>>,
-    pub terminator: Terminator<'a>,
+    pub terminator: Terminator,
 }
 
 #[derive(Clone, Debug)]
 pub struct Inst<'a> {
     pub operator: Operator<'a>,
     pub outputs: Vec<ValueId>,
-    pub inputs: Vec<Operand<'a>>,
+    pub inputs: Vec<Operand>,
 }
 
-#[derive(Clone, Debug)]
-pub enum Operand<'a> {
+#[derive(Clone, Copy, Debug)]
+pub enum Operand {
     /// An SSA value.
     Value(ValueId),
-    /// Tree-ified instructions for Wasm emission.
-    Sub(Box<Inst<'a>>),
     /// Undef values are produced when code is unreachable and thus
     /// removed/never executed.
     Undef,
 }
 
-impl<'a> Operand<'a> {
+impl Operand {
     pub fn value(value: ValueId) -> Self {
         if value == NO_VALUE {
             Operand::Undef
@@ -93,45 +92,90 @@ impl<'a> Operand<'a> {
 }
 
 #[derive(Clone, Debug)]
-pub struct BlockTarget<'a> {
+pub struct BlockTarget {
     pub block: BlockId,
-    pub args: Vec<Operand<'a>>,
+    pub args: Vec<Operand>,
 }
 
 #[derive(Clone, Debug)]
-pub enum Terminator<'a> {
+pub enum Terminator {
     Br {
-        target: BlockTarget<'a>,
+        target: BlockTarget,
     },
     CondBr {
-        cond: Operand<'a>,
-        if_true: BlockTarget<'a>,
-        if_false: BlockTarget<'a>,
+        cond: Operand,
+        if_true: BlockTarget,
+        if_false: BlockTarget,
     },
     Select {
-        value: Operand<'a>,
-        targets: Vec<BlockTarget<'a>>,
-        default: BlockTarget<'a>,
+        value: Operand,
+        targets: Vec<BlockTarget>,
+        default: BlockTarget,
     },
     Return {
-        values: Vec<Operand<'a>>,
+        values: Vec<Operand>,
     },
     None,
 }
 
-impl<'a> std::default::Default for Terminator<'a> {
+impl std::default::Default for Terminator {
     fn default() -> Self {
         Terminator::None
     }
 }
 
+impl Terminator {
+    pub fn args(&self) -> Vec<Operand> {
+        match self {
+            Terminator::Br { target } => target.args.clone(),
+            Terminator::CondBr {
+                cond,
+                if_true,
+                if_false,
+            } => {
+                let mut ret = vec![*cond];
+                ret.extend(if_true.args.iter().cloned());
+                ret.extend(if_false.args.iter().cloned());
+                ret
+            }
+            Terminator::Select {
+                value,
+                targets,
+                default,
+            } => {
+                let mut ret = vec![*value];
+                for target in targets {
+                    ret.extend(target.args.iter().cloned());
+                }
+                ret.extend(default.args.clone());
+                ret
+            }
+            Terminator::Return { values } => values.clone(),
+            Terminator::None => vec![],
+        }
+    }
+}
+
 impl<'a> Module<'a> {
     pub fn from_wasm_bytes(bytes: &'a [u8]) -> Result<Self> {
         frontend::wasm_to_ir(bytes)
     }
+
+    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()
+    }
 }
 
-impl<'a> Terminator<'a> {
+impl Terminator {
     pub fn successors(&self) -> Vec<BlockId> {
         match self {
             Terminator::Return { .. } => vec![],

src/lib.rs

@@ -7,6 +7,7 @@
 pub use wasm_encoder;
 pub use wasmparser;
 
+mod backend;
 mod dataflow;
 mod frontend;
 mod ir;