Revamp statement block optimization.

src/optimize.rs

@@ -88,11 +88,6 @@ impl<'a> State<'a> {
             optimization_level,
         }
     }
-    /// Reset the state from dirty to clean.
-    #[inline(always)]
-    pub fn reset(&mut self) {
-        self.changed = false;
-    }
     /// Set the [`AST`] state to be dirty (i.e. changed).
     #[inline(always)]
     pub fn set_dirty(&mut self) {
@@ -179,6 +174,8 @@ fn optimize_stmt_block(
     mut statements: Vec<Stmt>,
     state: &mut State,
     preserve_result: bool,
+    is_internal: bool,
+    reduce_return: bool,
 ) -> Vec<Stmt> {
     if statements.is_empty() {
         return statements;
@@ -186,6 +183,12 @@ fn optimize_stmt_block(
 
     let mut is_dirty = state.is_dirty();
 
+    let is_pure = if is_internal {
+        Stmt::is_internally_pure
+    } else {
+        Stmt::is_pure
+    };
+
     loop {
         state.clear_dirty();
 
@@ -228,18 +231,89 @@ fn optimize_stmt_block(
             }
         });
 
+        // Remove all pure statements except the last one
+        let mut index = 0;
+        let mut first_non_constant = statements
+            .iter()
+            .rev()
+            .enumerate()
+            .find_map(|(i, stmt)| match stmt {
+                stmt if !is_pure(stmt) => Some(i),
+
+                Stmt::Noop(_) | Stmt::Return(_, None, _) | Stmt::Export(_, _) | Stmt::Share(_) => {
+                    None
+                }
+
+                Stmt::Let(e, _, _, _)
+                | Stmt::Const(e, _, _, _)
+                | Stmt::Expr(e)
+                | Stmt::Return(_, Some(e), _)
+                | Stmt::Import(e, _, _)
+                    if e.is_constant() =>
+                {
+                    None
+                }
+
+                _ => Some(i),
+            })
+            .map_or(0, |n| statements.len() - n);
+
+        while index < statements.len() {
+            if preserve_result && index >= statements.len() - 1 {
+                break;
+            } else {
+                match &statements[index] {
+                    stmt if is_pure(stmt) && index >= first_non_constant => {
+                        state.set_dirty();
+                        statements.remove(index);
+                    }
+                    stmt if stmt.is_pure() => {
+                        state.set_dirty();
+                        if index < first_non_constant {
+                            first_non_constant -= 1;
+                        }
+                        statements.remove(index);
+                    }
+                    _ => index += 1,
+                }
+            }
+        }
+
         // Remove all pure statements that do not return values at the end of a block.
         // We cannot remove anything for non-pure statements due to potential side-effects.
         if preserve_result {
             loop {
-                match &statements[..] {
+                match &mut statements[..] {
-                    [stmt] if !stmt.returns_value() && stmt.is_internally_pure() => {
+                    // { return; } -> {}
+                    [Stmt::Return(crate::ast::ReturnType::Return, None, _)] if reduce_return => {
                         state.set_dirty();
                         statements.clear();
                     }
+                    [stmt] if !stmt.returns_value() && is_pure(stmt) => {
+                        state.set_dirty();
+                        statements.clear();
+                    }
+                    // { ...; return; } -> { ... }
+                    [.., last_stmt, Stmt::Return(crate::ast::ReturnType::Return, None, _)]
+                        if reduce_return && !last_stmt.returns_value() =>
+                    {
+                        state.set_dirty();
+                        statements.pop().unwrap();
+                    }
+                    // { ...; return val; } -> { ...; val }
+                    [.., Stmt::Return(crate::ast::ReturnType::Return, expr, pos)]
+                        if reduce_return =>
+                    {
+                        state.set_dirty();
+                        *statements.last_mut().unwrap() = if let Some(expr) = expr {
+                            Stmt::Expr(mem::take(expr))
+                        } else {
+                            Stmt::Noop(*pos)
+                        };
+                    }
                     [.., second_last_stmt, Stmt::Noop(_)] if second_last_stmt.returns_value() => {}
                     [.., second_last_stmt, last_stmt]
-                        if !last_stmt.returns_value() && last_stmt.is_internally_pure() =>
+                        if !last_stmt.returns_value() && is_pure(last_stmt) =>
                     {
                         state.set_dirty();
                         if second_last_stmt.returns_value() {
@@ -254,11 +328,25 @@ fn optimize_stmt_block(
         } else {
             loop {
                 match &statements[..] {
-                    [stmt] if stmt.is_internally_pure() => {
+                    [stmt] if is_pure(stmt) => {
                         state.set_dirty();
                         statements.clear();
                     }
-                    [.., last_stmt] if last_stmt.is_internally_pure() => {
+                    // { ...; return; } -> { ... }
+                    [.., Stmt::Return(crate::ast::ReturnType::Return, None, _)]
+                        if reduce_return =>
+                    {
+                        state.set_dirty();
+                        statements.pop().unwrap();
+                    }
+                    // { ...; return pure_val; } -> { ... }
+                    [.., Stmt::Return(crate::ast::ReturnType::Return, Some(expr), _)]
+                        if reduce_return && expr.is_pure() =>
+                    {
+                        state.set_dirty();
+                        statements.pop().unwrap();
+                    }
+                    [.., last_stmt] if is_pure(last_stmt) => {
                         state.set_dirty();
                         statements.pop().unwrap();
                     }
@@ -282,6 +370,9 @@ fn optimize_stmt_block(
         state.set_dirty();
     }
 
+    println!("{:?}", statements);
+
+    statements.shrink_to_fit();
     statements
 }
 
@@ -321,11 +412,8 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
         // if false { if_block } else { else_block } -> else_block
         Stmt::If(Expr::BoolConstant(false, _), x, _) => {
             state.set_dirty();
-            *stmt = match optimize_stmt_block(
+            let else_block = mem::take(&mut x.1.statements).into_vec();
-                mem::take(&mut x.1.statements).into_vec(),
+            *stmt = match optimize_stmt_block(else_block, state, preserve_result, true, false) {
-                state,
-                preserve_result,
-            ) {
                 statements if statements.is_empty() => Stmt::Noop(x.1.pos),
                 statements => Stmt::Block(statements, x.1.pos),
             }
@@ -333,11 +421,8 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
         // if true { if_block } else { else_block } -> if_block
         Stmt::If(Expr::BoolConstant(true, _), x, _) => {
             state.set_dirty();
-            *stmt = match optimize_stmt_block(
+            let if_block = mem::take(&mut x.0.statements).into_vec();
-                mem::take(&mut x.0.statements).into_vec(),
+            *stmt = match optimize_stmt_block(if_block, state, preserve_result, true, false) {
-                state,
-                preserve_result,
-            ) {
                 statements if statements.is_empty() => Stmt::Noop(x.0.pos),
                 statements => Stmt::Block(statements, x.0.pos),
             }
@@ -345,18 +430,12 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
         // if expr { if_block } else { else_block }
         Stmt::If(condition, x, _) => {
             optimize_expr(condition, state);
-            x.0.statements = optimize_stmt_block(
+            let if_block = mem::take(&mut x.0.statements).into_vec();
-                mem::take(&mut x.0.statements).into_vec(),
+            x.0.statements =
-                state,
+                optimize_stmt_block(if_block, state, preserve_result, true, false).into();
-                preserve_result,
+            let else_block = mem::take(&mut x.1.statements).into_vec();
-            )
+            x.1.statements =
-            .into();
+                optimize_stmt_block(else_block, state, preserve_result, true, false).into();
-            x.1.statements = optimize_stmt_block(
-                mem::take(&mut x.1.statements).into_vec(),
-                state,
-                preserve_result,
-            )
-            .into();
         }
 
         // switch const { ... }
@@ -371,15 +450,15 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
             let table = &mut x.0;
 
             let (statements, new_pos) = if let Some(block) = table.get_mut(&hash) {
+                let match_block = mem::take(&mut block.statements).into_vec();
                 (
-                    optimize_stmt_block(mem::take(&mut block.statements).into_vec(), state, true)
+                    optimize_stmt_block(match_block, state, true, true, false).into(),
-                        .into(),
                     block.pos,
                 )
             } else {
+                let def_block = mem::take(&mut x.1.statements).into_vec();
                 (
-                    optimize_stmt_block(mem::take(&mut x.1.statements).into_vec(), state, true)
+                    optimize_stmt_block(def_block, state, true, true, false).into(),
-                        .into(),
                     if x.1.pos.is_none() { *pos } else { x.1.pos },
                 )
             };
@@ -393,19 +472,13 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
         Stmt::Switch(expr, x, _) => {
             optimize_expr(expr, state);
             x.0.values_mut().for_each(|block| {
-                block.statements = optimize_stmt_block(
+                let match_block = mem::take(&mut block.statements).into_vec();
-                    mem::take(&mut block.statements).into_vec(),
+                block.statements =
-                    state,
+                    optimize_stmt_block(match_block, state, preserve_result, true, false).into()
-                    preserve_result,
-                )
-                .into()
             });
-            x.1.statements = optimize_stmt_block(
+            let def_block = mem::take(&mut x.1.statements).into_vec();
-                mem::take(&mut x.1.statements).into_vec(),
+            x.1.statements =
-                state,
+                optimize_stmt_block(def_block, state, preserve_result, true, false).into()
-                preserve_result,
-            )
-            .into()
         }
 
         // while false { block } -> Noop
@@ -414,15 +487,14 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
             *stmt = Stmt::Noop(*pos)
         }
         // while expr { block }
-        Stmt::While(condition, block, _) => {
+        Stmt::While(condition, body, _) => {
             optimize_expr(condition, state);
 
-            block.statements =
+            let block = mem::take(&mut body.statements).into_vec();
-                optimize_stmt_block(mem::take(&mut block.statements).into_vec(), state, false)
+            body.statements = optimize_stmt_block(block, state, false, true, false).into();
-                    .into();
 
-            if block.len() == 1 {
+            if body.len() == 1 {
-                match block.statements[0] {
+                match body.statements[0] {
                     // while expr { break; } -> { expr; }
                     Stmt::Break(pos) => {
                         // Only a single break statement - turn into running the guard expression once
@@ -442,26 +514,26 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
             }
         }
         // do { block } while false | do { block } until true -> { block }
-        Stmt::Do(block, Expr::BoolConstant(true, _), false, _)
+        Stmt::Do(body, Expr::BoolConstant(true, _), false, _)
-        | Stmt::Do(block, Expr::BoolConstant(false, _), true, _) => {
+        | Stmt::Do(body, Expr::BoolConstant(false, _), true, _) => {
             state.set_dirty();
+            let block = mem::take(&mut body.statements).into_vec();
             *stmt = Stmt::Block(
-                optimize_stmt_block(mem::take(&mut block.statements).into_vec(), state, false),
+                optimize_stmt_block(block, state, false, true, false),
-                block.pos,
+                body.pos,
             );
         }
         // do { block } while|until expr
-        Stmt::Do(block, condition, _, _) => {
+        Stmt::Do(body, condition, _, _) => {
             optimize_expr(condition, state);
-            block.statements =
+            let block = mem::take(&mut body.statements).into_vec();
-                optimize_stmt_block(mem::take(&mut block.statements).into_vec(), state, false)
+            body.statements = optimize_stmt_block(block, state, false, true, false).into();
-                    .into();
         }
         // for id in expr { block }
         Stmt::For(iterable, x, _) => {
             optimize_expr(iterable, state);
-            x.1.statements =
+            let body = mem::take(&mut x.1.statements).into_vec();
-                optimize_stmt_block(mem::take(&mut x.1.statements).into_vec(), state, false).into();
+            x.1.statements = optimize_stmt_block(body, state, false, true, false).into();
         }
         // let id = expr;
         Stmt::Let(expr, _, _, _) => optimize_expr(expr, state),
@@ -470,7 +542,8 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
         Stmt::Import(expr, _, _) => optimize_expr(expr, state),
         // { block }
         Stmt::Block(statements, pos) => {
-            *stmt = match optimize_stmt_block(mem::take(statements), state, preserve_result) {
+            let block = mem::take(statements);
+            *stmt = match optimize_stmt_block(block, state, preserve_result, true, false) {
                 statements if statements.is_empty() => {
                     state.set_dirty();
                     Stmt::Noop(*pos)
@@ -483,21 +556,22 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
                 statements => Stmt::Block(statements, *pos),
             };
         }
-        // try { pure block } catch ( var ) { block }
+        // try { pure try_block } catch ( var ) { catch_block } -> try_block
         Stmt::TryCatch(x, _, _) if x.0.statements.iter().all(Stmt::is_pure) => {
             // If try block is pure, there will never be any exceptions
             state.set_dirty();
+            let try_block = mem::take(&mut x.0.statements).into_vec();
             *stmt = Stmt::Block(
-                optimize_stmt_block(mem::take(&mut x.0.statements).into_vec(), state, false),
+                optimize_stmt_block(try_block, state, false, true, false),
                 x.0.pos,
             );
         }
-        // try { block } catch ( var ) { block }
+        // try { try_block } catch ( var ) { catch_block }
         Stmt::TryCatch(x, _, _) => {
-            x.0.statements =
+            let try_block = mem::take(&mut x.0.statements).into_vec();
-                optimize_stmt_block(mem::take(&mut x.0.statements).into_vec(), state, false).into();
+            x.0.statements = optimize_stmt_block(try_block, state, false, true, false).into();
-            x.2.statements =
+            let catch_block = mem::take(&mut x.2.statements).into_vec();
-                optimize_stmt_block(mem::take(&mut x.2.statements).into_vec(), state, false).into();
+            x.2.statements = optimize_stmt_block(catch_block, state, false, true, false).into();
         }
         // {}
         Stmt::Expr(Expr::Stmt(x)) if x.statements.is_empty() => {
@@ -532,7 +606,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
         // {}
         Expr::Stmt(x) if x.statements.is_empty() => { state.set_dirty(); *expr = Expr::Unit(x.pos) }
         // { stmt; ... } - do not count promotion as dirty because it gets turned back into an array
-        Expr::Stmt(x) => x.statements = optimize_stmt_block(mem::take(&mut x.statements).into_vec(), state, true).into(),
+        Expr::Stmt(x) => x.statements = optimize_stmt_block(mem::take(&mut x.statements).into_vec(), state, true, true, false).into(),
         // lhs.rhs
         #[cfg(not(feature = "no_object"))]
         Expr::Dot(x, _) => match (&mut x.lhs, &mut x.rhs) {
@@ -785,62 +859,7 @@ fn optimize_top_level(
         }
     });
 
-    let orig_constants_len = state.variables.len();
+    statements = optimize_stmt_block(statements, &mut state, true, false, true);
-
-    // Optimization loop
-    loop {
-        state.reset();
-        state.restore_var(orig_constants_len);
-
-        let num_statements = statements.len();
-
-        statements.iter_mut().enumerate().for_each(|(i, stmt)| {
-            match stmt {
-                Stmt::Const(value_expr, Ident { name, .. }, _, _) => {
-                    // Load constants
-                    optimize_expr(value_expr, &mut state);
-
-                    if value_expr.is_constant() {
-                        state.push_var(name, AccessMode::ReadOnly, value_expr.clone());
-                    }
-                }
-                Stmt::Let(value_expr, Ident { name, pos, .. }, _, _) => {
-                    optimize_expr(value_expr, &mut state);
-                    state.push_var(name, AccessMode::ReadWrite, Expr::Unit(*pos));
-                }
-                _ => {
-                    // Keep all variable declarations at this level
-                    // and always keep the last return value
-                    let keep = match stmt {
-                        Stmt::Let(_, _, _, _) | Stmt::Const(_, _, _, _) => true,
-                        #[cfg(not(feature = "no_module"))]
-                        Stmt::Import(_, _, _) => true,
-                        _ => i >= num_statements - 1,
-                    };
-                    optimize_stmt(stmt, &mut state, keep);
-                }
-            }
-        });
-
-        if !state.is_dirty() {
-            break;
-        }
-    }
-
-    // Eliminate code that is pure but always keep the last statement
-    let last_stmt = statements.pop();
-
-    // Remove all pure statements at global level
-    statements.retain(|stmt| !stmt.is_pure());
-
-    // Add back the last statement unless it is a lone No-op
-    if let Some(stmt) = last_stmt {
-        if !statements.is_empty() || !stmt.is_noop() {
-            statements.push(stmt);
-        }
-    }
-
-    statements.shrink_to_fit();
     statements
 }
 
@@ -895,34 +914,10 @@ pub fn optimize_into_ast(
 
                     let mut body = fn_def.body.statements.into_vec();
 
-                    loop {
+                    // Optimize the function body
-                        // Optimize the function body
+                    let state = &mut State::new(engine, lib2, level);
-                        let state = &mut State::new(engine, lib2, level);
 
-                        body = optimize_stmt_block(body, state, true);
+                    body = optimize_stmt_block(body, state, true, true, true);
-
-                        match &mut body[..] {
-                            // { return; } -> {}
-                            [Stmt::Return(crate::ast::ReturnType::Return, None, _)] => {
-                                body.clear();
-                            }
-                            // { ...; return; } -> { ... }
-                            [.., last_stmt, Stmt::Return(crate::ast::ReturnType::Return, None, _)]
-                                if !last_stmt.returns_value() =>
-                            {
-                                body.pop().unwrap();
-                            }
-                            // { ...; return val; } -> { ...; val }
-                            [.., Stmt::Return(crate::ast::ReturnType::Return, expr, pos)] => {
-                                *body.last_mut().unwrap() = if let Some(expr) = expr {
-                                    Stmt::Expr(mem::take(expr))
-                                } else {
-                                    Stmt::Noop(*pos)
-                                };
-                            }
-                            _ => break,
-                        }
-                    }
 
                     fn_def.body = StmtBlock {
                         statements: body.into(),

tests/optimizer.rs

@@ -55,7 +55,13 @@ fn test_optimizer_parse() -> Result<(), Box<EvalAltResult>> {
 
     let ast = engine.compile("{ const DECISION = false; if DECISION { 42 } else { 123 } }")?;
 
-    assert!(format!("{:?}", ast).starts_with(r#"AST { source: None, body: [Block([Const(BoolConstant(false, 1:20), Ident("DECISION" @ 1:9), false, 1:3), Expr(IntegerConstant(123, 1:53))], 1:1)], functions: Module("#));
+    assert!(format!("{:?}", ast).starts_with(
+        r#"AST { source: None, body: [Expr(IntegerConstant(123, 1:53))], functions: Module("#
+    ));
+
+    let ast = engine.compile("const DECISION = false; if DECISION { 42 } else { 123 }")?;
+
+    assert!(format!("{:?}", ast).starts_with(r#"AST { source: None, body: [Const(BoolConstant(false, 1:18), Ident("DECISION" @ 1:7), false, 1:1), Expr(IntegerConstant(123, 1:51))], functions: Module("#));
 
     let ast = engine.compile("if 1 == 2 { 42 }")?;