Unroll switch ranges if possible.

CHANGELOG.md

@@ -17,6 +17,7 @@ Enhancements
 * `switch` cases can now include multiple values separated by `|`.
 * `EvalContext::eval_expression_tree_raw` and `Expression::eval_with_context_raw` are added to allow for not rewinding the `Scope` at the end of a statements block.
 * A new `range` function variant that takes an exclusive range with a step.
+* Ranges in `switch` statements that are small (currently no more than 16 items) are unrolled if possible.
 
 
 Version 1.8.0

src/ast/stmt.rs

@@ -175,7 +175,6 @@ impl fmt::Debug for RangeCase {
 
 impl From<Range<INT>> for RangeCase {
     #[inline(always)]
-    #[must_use]
     fn from(value: Range<INT>) -> Self {
         Self::ExclusiveInt(value, 0)
     }
@@ -183,12 +182,24 @@ impl From<Range<INT>> for RangeCase {
 
 impl From<RangeInclusive<INT>> for RangeCase {
     #[inline(always)]
-    #[must_use]
     fn from(value: RangeInclusive<INT>) -> Self {
         Self::InclusiveInt(value, 0)
     }
 }
 
+impl IntoIterator for RangeCase {
+    type Item = INT;
+    type IntoIter = Box<dyn Iterator<Item = Self::Item>>;
+
+    #[inline(always)]
+    fn into_iter(self) -> Self::IntoIter {
+        match self {
+            Self::ExclusiveInt(r, ..) => Box::new(r.into_iter()),
+            Self::InclusiveInt(r, ..) => Box::new(r.into_iter()),
+        }
+    }
+}
+
 impl RangeCase {
     /// Is the range empty?
     #[inline(always)]
@@ -199,6 +210,17 @@ impl RangeCase {
             Self::InclusiveInt(r, ..) => r.is_empty(),
         }
     }
+    /// Size of the range.
+    #[inline(always)]
+    #[must_use]
+    pub fn len(&self) -> usize {
+        match self {
+            Self::ExclusiveInt(r, ..) if r.is_empty() => 0,
+            Self::ExclusiveInt(r, ..) => (r.end - r.start) as usize,
+            Self::InclusiveInt(r, ..) if r.is_empty() => 0,
+            Self::InclusiveInt(r, ..) => (*r.end() - *r.start()) as usize,
+        }
+    }
     /// Is the specified number within this range?
     #[inline(always)]
     #[must_use]
@@ -208,19 +230,6 @@ impl RangeCase {
             Self::InclusiveInt(r, ..) => r.contains(&n),
         }
     }
-    /// If the range contains only of a single [`INT`], return it;
-    /// otherwise return [`None`].
-    #[inline(always)]
-    #[must_use]
-    pub fn single_int(&self) -> Option<INT> {
-        match self {
-            Self::ExclusiveInt(r, ..) if r.end.checked_sub(r.start) == Some(1) => Some(r.start),
-            Self::InclusiveInt(r, ..) if r.end().checked_sub(*r.start()) == Some(0) => {
-                Some(*r.start())
-            }
-            _ => None,
-        }
-    }
     /// Is the specified range inclusive?
     #[inline(always)]
     #[must_use]

src/optimizer.rs

@@ -525,7 +525,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             let (
                 match_expr,
                 SwitchCases {
-                    blocks: blocks_list,
+                    blocks,
                     cases,
                     ranges,
                     def_case,
@@ -538,29 +538,29 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             let hash = hasher.finish();
 
             // First check hashes
-            if let Some(block) = cases.remove(&hash) {
+            if let Some(b) = cases.remove(&hash) {
-                let mut block = mem::take(&mut blocks_list[block]);
+                let mut b = mem::take(&mut blocks[b]);
                 cases.clear();
 
-                match block.condition {
+                match b.condition {
                     Expr::BoolConstant(true, ..) => {
                         // Promote the matched case
-                        let statements: StmtBlockContainer = mem::take(&mut block.statements);
+                        let statements: StmtBlockContainer = mem::take(&mut b.statements);
                         let statements = optimize_stmt_block(statements, state, true, true, false);
-                        *stmt = (statements, block.statements.span()).into();
+                        *stmt = (statements, b.statements.span()).into();
                     }
                     ref mut condition => {
                         // switch const { case if condition => stmt, _ => def } => if condition { stmt } else { def }
                         optimize_expr(condition, state, false);
 
-                        let def_case = &mut blocks_list[*def_case].statements;
+                        let def_case = &mut blocks[*def_case].statements;
                         let def_span = def_case.span_or_else(*pos, Position::NONE);
                         let def_case: StmtBlockContainer = mem::take(def_case);
                         let def_stmt = optimize_stmt_block(def_case, state, true, true, false);
                         *stmt = Stmt::If(
                             (
                                 mem::take(condition),
-                                mem::take(&mut block.statements),
+                                mem::take(&mut b.statements),
                                 StmtBlock::new_with_span(def_stmt, def_span),
                             )
                                 .into(),
@@ -580,19 +580,16 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                 // Only one range or all ranges without conditions
                 if ranges.len() == 1
                     || ranges.iter().all(|r| {
-                        matches!(
+                        matches!(blocks[r.index()].condition, Expr::BoolConstant(true, ..))
-                            blocks_list[r.index()].condition,
-                            Expr::BoolConstant(true, ..)
-                        )
                     })
                 {
                     for r in ranges.iter().filter(|r| r.contains(value)) {
-                        let condition = mem::take(&mut blocks_list[r.index()].condition);
+                        let condition = mem::take(&mut blocks[r.index()].condition);
 
                         match condition {
                             Expr::BoolConstant(true, ..) => {
                                 // Promote the matched case
-                                let block = &mut blocks_list[r.index()];
+                                let block = &mut blocks[r.index()];
                                 let statements = mem::take(&mut *block.statements);
                                 let statements =
                                     optimize_stmt_block(statements, state, true, true, false);
@@ -602,13 +599,13 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                                 // switch const { range if condition => stmt, _ => def } => if condition { stmt } else { def }
                                 optimize_expr(&mut condition, state, false);
 
-                                let def_case = &mut blocks_list[*def_case].statements;
+                                let def_case = &mut blocks[*def_case].statements;
                                 let def_span = def_case.span_or_else(*pos, Position::NONE);
                                 let def_case: StmtBlockContainer = mem::take(def_case);
                                 let def_stmt =
                                     optimize_stmt_block(def_case, state, true, true, false);
 
-                                let statements = mem::take(&mut blocks_list[r.index()].statements);
+                                let statements = mem::take(&mut blocks[r.index()].statements);
 
                                 *stmt = Stmt::If(
                                     (
@@ -641,16 +638,16 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                     }
 
                     for r in &*ranges {
-                        let block = &mut blocks_list[r.index()];
+                        let b = &mut blocks[r.index()];
-                        let statements = mem::take(&mut *block.statements);
+                        let statements = mem::take(&mut *b.statements);
-                        *block.statements =
+                        *b.statements =
                             optimize_stmt_block(statements, state, preserve_result, true, false);
 
-                        optimize_expr(&mut block.condition, state, false);
+                        optimize_expr(&mut b.condition, state, false);
 
-                        match block.condition {
+                        match b.condition {
                             Expr::Unit(pos) => {
-                                block.condition = Expr::BoolConstant(true, pos);
+                                b.condition = Expr::BoolConstant(true, pos);
                                 state.set_dirty()
                             }
                             _ => (),
@@ -662,7 +659,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
 
             // Promote the default case
             state.set_dirty();
-            let def_case = &mut blocks_list[*def_case].statements;
+            let def_case = &mut blocks[*def_case].statements;
             let def_span = def_case.span_or_else(*pos, Position::NONE);
             let def_case: StmtBlockContainer = mem::take(def_case);
             let def_stmt = optimize_stmt_block(def_case, state, true, true, false);
@@ -673,7 +670,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             let (
                 match_expr,
                 SwitchCases {
-                    blocks: blocks_list,
+                    blocks,
                     cases,
                     ranges,
                     def_case,
@@ -684,21 +681,21 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             optimize_expr(match_expr, state, false);
 
             // Optimize blocks
-            for block in blocks_list.iter_mut() {
+            for b in blocks.iter_mut() {
-                let statements = mem::take(&mut *block.statements);
+                let statements = mem::take(&mut *b.statements);
-                *block.statements =
+                *b.statements =
                     optimize_stmt_block(statements, state, preserve_result, true, false);
 
-                optimize_expr(&mut block.condition, state, false);
+                optimize_expr(&mut b.condition, state, false);
 
-                match block.condition {
+                match b.condition {
                     Expr::Unit(pos) => {
-                        block.condition = Expr::BoolConstant(true, pos);
+                        b.condition = Expr::BoolConstant(true, pos);
                         state.set_dirty();
                     }
                     Expr::BoolConstant(false, ..) => {
-                        if !block.statements.is_empty() {
+                        if !b.statements.is_empty() {
-                            block.statements = StmtBlock::NONE;
+                            b.statements = StmtBlock::NONE;
                             state.set_dirty();
                         }
                     }
@@ -707,7 +704,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             }
 
             // Remove false cases
-            cases.retain(|_, &mut block| match blocks_list[block].condition {
+            cases.retain(|_, &mut block| match blocks[block].condition {
                 Expr::BoolConstant(false, ..) => {
                     state.set_dirty();
                     false
@@ -715,7 +712,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                 _ => true,
             });
             // Remove false ranges
-            ranges.retain(|r| match blocks_list[r.index()].condition {
+            ranges.retain(|r| match blocks[r.index()].condition {
                 Expr::BoolConstant(false, ..) => {
                     state.set_dirty();
                     false
@@ -723,9 +720,26 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                 _ => true,
             });
 
-            let def_case = &mut blocks_list[*def_case].statements;
+            let def_stmt_block = &mut blocks[*def_case].statements;
-            let def_block = mem::take(&mut **def_case);
+            let def_block = mem::take(&mut **def_stmt_block);
-            **def_case = optimize_stmt_block(def_block, state, preserve_result, true, false);
+            **def_stmt_block = optimize_stmt_block(def_block, state, preserve_result, true, false);
+
+            // Remove unused block statements
+            for index in 0..blocks.len() {
+                if *def_case == index
+                    || cases.values().any(|&n| n == index)
+                    || ranges.iter().any(|r| r.index() == index)
+                {
+                    continue;
+                }
+
+                let b = &mut blocks[index];
+
+                if !b.statements.is_empty() {
+                    b.statements = StmtBlock::NONE;
+                    state.set_dirty();
+                }
+            }
         }
 
         // while false { block } -> Noop

src/parser.rs

@@ -39,6 +39,9 @@ const SCOPE_SEARCH_BARRIER_MARKER: &str = "$ BARRIER $";
 /// The message: `TokenStream` never ends
 const NEVER_ENDS: &str = "`Token`";
 
+/// Unroll `switch` ranges no larger than this.
+const SMALL_SWITCH_RANGE: usize = 16;
+
 /// _(internals)_ A type that encapsulates the current state of the parser.
 /// Exported under the `internals` feature only.
 pub struct ParseState<'e> {
@@ -1138,6 +1141,7 @@ impl Engine {
 
             let stmt = self.parse_stmt(input, state, lib, settings.level_up())?;
             let need_comma = !stmt.is_self_terminated();
+            let has_condition = !matches!(condition, Expr::BoolConstant(true, ..));
 
             blocks.push((condition, stmt).into());
             let index = blocks.len() - 1;
@@ -1159,14 +1163,15 @@ impl Engine {
 
                     if let Some(mut r) = range_value {
                         if !r.is_empty() {
-                            if let Some(n) = r.single_int() {
+                            // Do not unroll ranges if there are previous non-unrolled ranges
-                                // Unroll single range
+                            if !has_condition && ranges.is_empty() && r.len() <= SMALL_SWITCH_RANGE
-                                let value = Dynamic::from_int(n);
+                            {
-                                let hasher = &mut get_hasher();
+                                // Unroll small range
-                                value.hash(hasher);
+                                for n in r {
-                                let hash = hasher.finish();
+                                    let hasher = &mut get_hasher();
-
+                                    Dynamic::from_int(n).hash(hasher);
-                                cases.entry(hash).or_insert(index);
+                                    cases.entry(hasher.finish()).or_insert(index);
+                                }
                             } else {
                                 // Other range
                                 r.set_index(index);

tests/switch.rs

@@ -290,6 +290,49 @@ fn test_switch_ranges() -> Result<(), Box<EvalAltResult>> {
         )?,
         'x'
     );
+    assert_eq!(
+        engine.eval_with_scope::<INT>(
+            &mut scope,
+            "
+                switch 5 {
+                    'a' => true,
+                    0..10 => 123,
+                    2..12 => 'z',
+                    _ => 'x'
+                }
+            "
+        )?,
+        123
+    );
+    assert_eq!(
+        engine.eval_with_scope::<INT>(
+            &mut scope,
+            "
+                switch 5 {
+                    'a' => true,
+                    4 | 5 | 6 => 42,
+                    0..10 => 123,
+                    2..12 => 'z',
+                    _ => 'x'
+                }
+            "
+        )?,
+        42
+    );
+    assert_eq!(
+        engine.eval_with_scope::<char>(
+            &mut scope,
+            "
+                switch 5 {
+                    'a' => true,
+                    2..12 => 'z',
+                    0..10 if x+2==1+2 => print(40+2),
+                    _ => 'x'
+                }
+            "
+        )?,
+        'z'
+    );
     assert_eq!(
         engine.eval_with_scope::<char>(
             &mut scope,