evaluate: remove anon sets with exactly one element

Auto-replace lookups in single-element anon sets with a standard compare.

'add rule foo bar meta iif { "lo" }' gets replaced with
'add rule foo bar meta iif "lo"'.

The former is a set lookup, the latter is a comparision.
Comparisions are faster for the one-element case.

Only prefixes, ranges and values are handled at this time.

Anonymous maps are left alone, same for concatenations.

Concatenations could be handled, but it would require more work:
the concatenation would have to be replaced with a singleton value.
Evaluation step rejects concat RHS on a relational expression.

Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 19 insertions, 2 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 384e2fa7..2ed68aad 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -1455,8 +1455,25 @@ static int expr_evaluate_set(struct eval_ctx *ctx, struct expr **expr)
 		}
 	}
 
-	if (ctx->set && (ctx->set->flags & NFT_SET_CONCAT))
-		set->set_flags |= NFT_SET_CONCAT;
+	if (ctx->set) {
+		if (ctx->set->flags & NFT_SET_CONCAT)
+			set->set_flags |= NFT_SET_CONCAT;
+	} else if (set->size == 1) {
+		i = list_first_entry(&set->expressions, struct expr, list);
+		if (i->etype == EXPR_SET_ELEM) {
+			switch (i->key->etype) {
+			case EXPR_PREFIX:
+			case EXPR_RANGE:
+			case EXPR_VALUE:
+				*expr = i->key;
+				i->key = NULL;
+				expr_free(set);
+				return 0;
+			default:
+				break;
+			}
+		}
+	}
 
 	set->set_flags |= NFT_SET_CONSTANT;