Implement unrachable BasicBlock elimination

Author: HalidOdat

boa_cli/src/debug/optimizer.rs

@@ -1,7 +1,9 @@
 use boa_engine::{
     object::{FunctionObjectBuilder, ObjectInitializer},
     optimizer::{
-        control_flow_graph::{ControlFlowGraph, GraphSimplification},
+        control_flow_graph::{
+            ControlFlowGraph, GraphEliminateUnreachableBasicBlocks, GraphSimplification,
+        },
         OptimizerOptions,
     },
     property::Attribute,
@@ -80,6 +82,9 @@ fn graph(_: &JsValue, args: &[JsValue], _context: &mut Context<'_>) -> JsResult<
     let changed = GraphSimplification::perform(&mut cfg);
     println!("Simplified({changed}) \n{:#?}", cfg);
 
+    let changed = GraphEliminateUnreachableBasicBlocks::perform(&mut cfg);
+    println!("Eliminate Unreachble({changed}) \n{:#?}", cfg);
+
     Ok(JsValue::undefined())
 }
 

boa_engine/src/optimizer/control_flow_graph/basic_block.rs

@@ -0,0 +1,213 @@
+use std::{
+    cell::RefCell,
+    hash::{Hash, Hasher},
+    ops::Deref,
+    rc::{Rc, Weak},
+};
+
+use bitflags::bitflags;
+
+use super::{
+    instruction_iterator::{InstructionIterator, InstructionIteratorResult},
+    Terminator,
+};
+
+bitflags! {
+    #[derive(Default, Clone, Copy, Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct BasicBlockFlags: u8 {
+        const REACHABLE = 0b0000_0001;
+    }
+}
+
+/// TODO: doc
+#[derive(Default, Clone)]
+pub struct BasicBlock {
+    pub(crate) predecessors: Vec<WeakBasicBlock>,
+    pub(crate) bytecode: Vec<u8>,
+    pub(crate) terminator: Terminator,
+
+    pub(crate) flags: BasicBlockFlags,
+}
+
+impl BasicBlock {
+    /// Get nth instruction in the [`BasicBlock`].
+    pub(crate) fn get(&mut self, nth: usize) -> Option<InstructionIteratorResult<'_>> {
+        InstructionIterator::new(&self.bytecode).nth(nth)
+    }
+
+    /// Insert nth instruction in the [`BasicBlock`].
+    pub(crate) fn insert(&mut self, nth: usize, instruction: &[u8]) -> bool {
+        let start = if let Some(value) = self.get(nth) {
+            value.next_opcode_pc
+        } else {
+            0
+        };
+
+        for i in 0..instruction.len() {
+            self.bytecode.insert(start + i, instruction[i]);
+        }
+
+        true
+    }
+
+    /// Insert instruction in the last position in the [`BasicBlock`].
+    pub(crate) fn insert_last(&mut self, instruction: &[u8]) -> bool {
+        let start = if let Some(value) = InstructionIterator::new(&self.bytecode).last() {
+            value.next_opcode_pc
+        } else {
+            0
+        };
+
+        for i in 0..instruction.len() {
+            self.bytecode.insert(start + i, instruction[i]);
+        }
+
+        true
+    }
+
+    /// Remove nth instruction in the [`BasicBlock`].
+    pub(crate) fn remove(&mut self, nth: usize) -> bool {
+        let Some(value) = self.get(nth) else {
+            return false;
+        };
+
+        let start = value.current_opcode_pc;
+        let length = value.next_opcode_pc - value.current_opcode_pc;
+
+        for i in 0..length {
+            self.bytecode.remove(start + i);
+        }
+
+        true
+    }
+
+    /// Remove last instruction in the [`BasicBlock`].
+    pub(crate) fn remove_last(&mut self) -> bool {
+        let Some(value) = InstructionIterator::new(&self.bytecode).last() else {
+            return false;
+        };
+
+        let start = value.current_opcode_pc;
+        let length = value.next_opcode_pc - value.current_opcode_pc;
+
+        for i in 0..length {
+            self.bytecode.remove(start + i);
+        }
+
+        true
+    }
+
+    pub(crate) fn reachable(&self) -> bool {
+        self.flags.contains(BasicBlockFlags::REACHABLE)
+    }
+
+    pub(crate) fn successors(&self) -> Vec<RcBasicBlock> {
+        match &self.terminator {
+            Terminator::None => vec![],
+            Terminator::JumpUnconditional { target, .. } => {
+                vec![target.clone()]
+            }
+            Terminator::JumpConditional { no, yes, .. } => {
+                vec![no.clone(), yes.clone()]
+            }
+            Terminator::Return { finally } => {
+                let mut successors = Vec::new();
+                if let Some(finally) = finally {
+                    successors.push(finally.clone());
+                }
+                successors
+            }
+        }
+    }
+
+    pub(crate) fn next(&self, nexts: &mut Vec<RcBasicBlock>) {
+        match &self.terminator {
+            Terminator::None => {}
+            Terminator::JumpUnconditional { target, .. } => {
+                nexts.push(target.clone());
+            }
+            Terminator::JumpConditional { no, yes, .. } => {
+                nexts.push(no.clone());
+                nexts.push(yes.clone());
+            }
+            Terminator::Return { finally } => {
+                if let Some(_finally) = finally {
+                    // FIXME: should we include this??
+                    // nexts.push(finally.clone());
+                }
+            }
+        }
+    }
+}
+
+/// Reference counted [`BasicBlock`] with interor mutability.
+#[derive(Default, Clone)]
+pub struct RcBasicBlock {
+    inner: Rc<RefCell<BasicBlock>>,
+}
+
+impl From<Rc<RefCell<BasicBlock>>> for RcBasicBlock {
+    fn from(inner: Rc<RefCell<BasicBlock>>) -> Self {
+        Self { inner }
+    }
+}
+
+impl Deref for RcBasicBlock {
+    type Target = Rc<RefCell<BasicBlock>>;
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl PartialEq<RcBasicBlock> for RcBasicBlock {
+    fn eq(&self, other: &RcBasicBlock) -> bool {
+        Rc::ptr_eq(&self.inner, &other.inner)
+    }
+}
+
+impl Eq for RcBasicBlock {}
+
+impl Hash for RcBasicBlock {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (self.as_ptr() as usize).hash(state);
+    }
+}
+
+impl RcBasicBlock {
+    /// TODO: doc
+    pub fn downgrade(&self) -> WeakBasicBlock {
+        WeakBasicBlock::from(Rc::downgrade(&self.inner))
+    }
+}
+
+/// Reference counted [`BasicBlock`] with interor mutability.
+#[derive(Default, Clone)]
+pub struct WeakBasicBlock {
+    inner: Weak<RefCell<BasicBlock>>,
+}
+
+impl From<Weak<RefCell<BasicBlock>>> for WeakBasicBlock {
+    fn from(inner: Weak<RefCell<BasicBlock>>) -> Self {
+        Self { inner }
+    }
+}
+
+impl Deref for WeakBasicBlock {
+    type Target = Weak<RefCell<BasicBlock>>;
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl PartialEq<WeakBasicBlock> for WeakBasicBlock {
+    fn eq(&self, other: &WeakBasicBlock) -> bool {
+        Weak::ptr_eq(&self.inner, &other.inner)
+    }
+}
+
+impl WeakBasicBlock {
+    /// TODO: doc
+    pub fn upgrade(&self) -> Option<RcBasicBlock> {
+        Some(RcBasicBlock::from(self.inner.upgrade()?))
+    }
+}