Typechecking 'for' statements

- condition in a 'for' must be bool

Signed-off-by: Chris Dodd <cdodd@nvidia.com>

Author: ChrisDodd

frontends/p4/typeChecking/readOnlyTypeInference.cpp

@@ -143,6 +143,7 @@ DEFINE_POSTORDER(IR::AssignmentStatement)
 DEFINE_POSTORDER(IR::OpAssignmentStatement)
 DEFINE_POSTORDER(IR::ShlAssign)
 DEFINE_POSTORDER(IR::ShrAssign)
+DEFINE_POSTORDER(IR::ForStatement)
 DEFINE_POSTORDER(IR::ForInStatement)
 DEFINE_POSTORDER(IR::ActionListElement)
 DEFINE_POSTORDER(IR::KeyElement)

frontends/p4/typeChecking/typeCheckStmt.cpp

@@ -18,6 +18,15 @@ limitations under the License.
 
 namespace P4 {
 
+const IR::Node *TypeInferenceBase::postorder(const IR::ForStatement *stmt) {
+    LOG3("TI Visiting " << dbp(getOriginal()));
+    auto type = getType(stmt->condition);
+    if (type == nullptr) return stmt;
+    if (!type->is<IR::Type_Boolean>())
+        typeError("Condition of %1% does not evaluate to a bool but %2%", stmt, type->toString());
+    return stmt;
+}
+
 const IR::Node *TypeInferenceBase::postorder(const IR::IfStatement *conditional) {
     LOG3("TI Visiting " << dbp(getOriginal()));
     auto type = getType(conditional->condition);

frontends/p4/typeChecking/typeChecker.h

@@ -326,6 +326,7 @@ class TypeInferenceBase : public virtual Visitor, public ResolutionContext {
     const IR::Node *postorder(const IR::ActionList *al);
 
     const IR::Node *postorder(const IR::ReturnStatement *stat);
+    const IR::Node *postorder(const IR::ForStatement *stat);
     const IR::Node *postorder(const IR::IfStatement *stat);
     const IR::Node *postorder(const IR::SwitchStatement *stat);
     const IR::Node *common_assign(const IR::BaseAssignmentStatement *stat, const IR::Type *);
@@ -474,6 +475,7 @@ class ReadOnlyTypeInference : public virtual Inspector, public TypeInferenceBase
     void postorder(const IR::ActionList *al) override;
 
     void postorder(const IR::ReturnStatement *stat) override;
+    void postorder(const IR::ForStatement *stat) override;
     void postorder(const IR::IfStatement *stat) override;
     void postorder(const IR::SwitchStatement *stat) override;
     void postorder(const IR::AssignmentStatement *stat) override;
@@ -613,6 +615,7 @@ class TypeInference : public virtual Transform, public TypeInferenceBase {
     const IR::Node *postorder(IR::ActionList *al) override;
 
     const IR::Node *postorder(IR::ReturnStatement *stat) override;
+    const IR::Node *postorder(IR::ForStatement *stat) override;
     const IR::Node *postorder(IR::IfStatement *stat) override;
     const IR::Node *postorder(IR::SwitchStatement *stat) override;
     const IR::Node *postorder(IR::AssignmentStatement *stat) override;

frontends/p4/typeChecking/typeInference.cpp

@@ -134,6 +134,7 @@ DEFINE_POSTORDER(IR::AssignmentStatement)
 DEFINE_POSTORDER(IR::OpAssignmentStatement)
 DEFINE_POSTORDER(IR::ShlAssign)
 DEFINE_POSTORDER(IR::ShrAssign)
+DEFINE_POSTORDER(IR::ForStatement)
 DEFINE_POSTORDER(IR::ForInStatement)
 DEFINE_POSTORDER(IR::ActionListElement)
 DEFINE_POSTORDER(IR::KeyElement)

testdata/p4_16_errors/loop4-err.p4

@@ -0,0 +1,15 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Nvidia Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+extern void fn(in bit<8> c);
+
+control c() {
+    apply {
+        for (bit<8> a = 15; a; a -= 1) {
+            fn(a);
+        }
+    }
+}

testdata/p4_16_errors_outputs/loop4-err.p4

@@ -0,0 +1,9 @@
+extern void fn(in bit<8> c);
+control c() {
+    apply {
+        for (bit<8> a = 15; a; a -= 1) {
+            fn(a);
+        }
+    }
+}
+

testdata/p4_16_errors_outputs/loop4-err.p4-stderr

@@ -0,0 +1,6 @@
+loop4-err.p4(9): [--Wwarn=unused] warning: control 'c' is unused
+control c() {
+        ^
+loop4-err.p4(11): [--Werror=type-error] error: Condition of ForStatement does not evaluate to a bool but bit<8>
+        for (bit<8> a = 15; a; a -= 1) {
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^