reduce number of allocations in deriv()

microsoft · Dec 18, 2024 · a629ecc · a629ecc
1 parent bded1a1
commit a629ecc
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Showing 2 changed files with 17 additions and 8 deletions.
diff --git a/src/ast.rs b/src/ast.rs
@@ -476,6 +476,8 @@ impl ExprSet {
         }
 
         let mut todo = vec![r];
+        let mut mapped = Vec::with_capacity(128);
+
         while let Some(r) = todo.last() {
             let r = *r;
             let idx = mk_key(r);
@@ -487,7 +489,7 @@ impl ExprSet {
             let is_concat = concat_nullable_check && matches!(e, Expr::Concat(_, _));
             let todo_len = todo.len();
             let eargs = e.args();
-            let mut mapped = Vec::with_capacity(eargs.len());
+            mapped.clear();
             for a in eargs {
                 let a = *a;
                 let brk = is_concat && !self.is_nullable(a);

diff --git a/src/deriv.rs b/src/deriv.rs
@@ -49,6 +49,9 @@ impl DerivCache {
             }
         }
 
+        let mut tmp = vec![];
+        let mut or_branches = vec![];
+
         // regular path
         exprs.map(
             r,
@@ -79,15 +82,19 @@ impl DerivCache {
                             max.saturating_sub(1)
                         };
                         let tail = exprs.mk_repeat(e, min.saturating_sub(1), max);
-                        exprs.mk_concat(&mut vec![deriv[0], tail])
+                        tmp.clear();
+                        tmp.push(deriv[0]);
+                        tmp.push(tail);
+                        exprs.mk_concat(&mut tmp)
                     }
                     Expr::Concat(_, args) => {
-                        let mut or_branches = vec![];
-                        let mut args = args.to_vec();
-                        for i in 0..args.len() {
-                            let nullable = exprs.is_nullable(args[i]);
-                            args[i] = deriv[i];
-                            or_branches.push(exprs.mk_concat(&mut args[i..].to_vec()));
+                        or_branches.clear();
+                        tmp.clear();
+                        tmp.extend_from_slice(args);
+                        for i in 0..tmp.len() {
+                            let nullable = exprs.is_nullable(tmp[i]);
+                            tmp[i] = deriv[i];
+                            or_branches.push(exprs.mk_concat(&mut tmp[i..].to_vec()));
                             if !nullable {
                                 break;
                             }