short circuit on constant branch conditions

changelogs/unreleased/1315-schaeff

@@ -0,0 +1 @@
+Short-circuit on compile-time constant branch conditions

zokrates_analysis/src/propagation.rs

@@ -181,26 +181,22 @@ impl<'ast, T: Field> ResultFolder<'ast, T> for Propagator<'ast, T> {
         _: &E::Ty,
         e: ConditionalExpression<'ast, T, E>,
     ) -> Result<ConditionalOrExpression<'ast, T, E>, Self::Error> {
-        Ok(
-            match (
-                self.fold_boolean_expression(*e.condition)?,
-                e.consequence.fold(self)?,
-                e.alternative.fold(self)?,
-            ) {
-                (BooleanExpression::Value(v), consequence, _) if v.value => {
+        Ok(match self.fold_boolean_expression(*e.condition)? {
+            BooleanExpression::Value(v) if v.value => {
+                ConditionalOrExpression::Expression(e.consequence.fold(self)?.into_inner())
+            }
+            BooleanExpression::Value(v) if !v.value => {
+                ConditionalOrExpression::Expression(e.alternative.fold(self)?.into_inner())
+            }
+            condition => match (e.consequence.fold(self)?, e.alternative.fold(self)?) {
+                (consequence, alternative) if consequence == alternative => {
                     ConditionalOrExpression::Expression(consequence.into_inner())
                 }
-                (BooleanExpression::Value(v), _, alternative) if !v.value => {
-                    ConditionalOrExpression::Expression(alternative.into_inner())
-                }
-                (_, consequence, alternative) if consequence == alternative => {
-                    ConditionalOrExpression::Expression(consequence.into_inner())
-                }
-                (condition, consequence, alternative) => ConditionalOrExpression::Conditional(
+                (consequence, alternative) => ConditionalOrExpression::Conditional(
                     ConditionalExpression::new(condition, consequence, alternative, e.kind),
                 ),
             },
-        )
+        })
     }
 
     fn fold_assembly_assignment(

zokrates_core_test/tests/tests/constant_condition.json

@@ -0,0 +1,3 @@
+{
+  "tests": []
+}

zokrates_core_test/tests/tests/constant_condition.zok

@@ -0,0 +1,6 @@
+def main() {
+    field[2] a = [0; 2];
+    for u32 i in 1..2 {
+        field b = (i == 1) ? 0 : a[i - 2];
+    }
+}