From ed3c87d253bea2d2e2675719f90a39b694982965 Mon Sep 17 00:00:00 2001
From: Vern Paxson <vern@corelight.com>
Date: Mon, 16 Aug 2021 10:38:42 -0700
Subject: [PATCH] simple AST optimization for ?: operator

---
 src/script_opt/Expr.cc | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/script_opt/Expr.cc b/src/script_opt/Expr.cc
index eede780b15..e54ca4dc37 100644
--- a/src/script_opt/Expr.cc
+++ b/src/script_opt/Expr.cc
@@ -1427,6 +1427,19 @@ ExprPtr CondExpr::Reduce(Reducer* c, StmtPtr& red_stmt)
 		return op2;
 		}
 
+	if ( op2->IsConst() && op3->IsConst() && GetType()->Tag() == TYPE_BOOL )
+		{
+		auto op2_t = op2->IsOne();
+		ASSERT(op2_t != op3->IsOne());
+
+		if ( op2_t )
+			// This is "var ? T : F", which can be replaced by var.
+			return op1;
+
+		// Instead we have "var ? F : T".
+		return make_intrusive<NotExpr>(op1);
+		}
+
 	if ( c->Optimizing() )
 		return ThisPtr();