clear done/visit_in_progress when revisiting node (#4608)

Reset the done/visit_in_progress flag when revisiting a node in
Visitor::Tracker::try_start or Visitor::ChangeTracker::try_start.

For inspectors, fixes a small regression introduced in #4447. For
Modifiers/Transforms, fixes a bug that hadn't been previously
encountered. (Bug revealed by test program.)

ir/visitor.cpp

@@ -78,6 +78,7 @@ class Visitor::ChangeTracker {
         if (!inserted) {  // We already seen this node, determine its status
             if (it->second.visit_in_progress) return VisitStatus::Busy;
             if (it->second.visitOnce) return VisitStatus::Done;
+            it->second.visit_in_progress = true;
             return VisitStatus::Revisit;
         }
 
@@ -250,6 +251,7 @@ class Visitor::Tracker {
         if (!inserted) {  // We already seen this node, determine its status
             if (!it->second.done) return VisitStatus::Busy;
             if (it->second.visitOnce) return VisitStatus::Done;
+            it->second.done = false;
             return VisitStatus::Revisit;
         }
 

test/CMakeLists.txt

@@ -53,6 +53,7 @@ set (GTEST_UNITTEST_SOURCES
   gtest/stringify.cpp
   gtest/rtti_test.cpp
   gtest/nethash.cpp
+  gtest/visitor.cpp
 )
 
 # Combine the executable and the non-backend-specific unit tests into a single

test/gtest/visitor.cpp

@@ -0,0 +1,163 @@
+/*
+Copyright 2024 Intel Corp.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+#include "frontends/common/parseInput.h"
+#include "frontends/common/resolveReferences/resolveReferences.h"
+#include "gtest/gtest.h"
+#include "helpers.h"
+#include "ir/ir.h"
+#include "midend_pass.h"
+
+namespace Test {
+
+using P4TestContext = P4CContextWithOptions<CompilerOptions>;
+
+class P4CVisitor : public P4CTest {};
+
+struct MultiVisitInspector : public Inspector, virtual public P4::ResolutionContext {
+    MultiVisitInspector() { visitDagOnce = false; }
+
+ private:
+    // ignore parser and declaration loops for now
+    void loop_revisit(const IR::ParserState *) override {}
+
+    void visit_def(const IR::PathExpression *pe) {
+        auto *d = resolveUnique(pe->path->name, P4::ResolutionType::Any);
+        BUG_CHECK(d, "failed to resolve %s", pe);
+        if (auto *ps = d->to<IR::ParserState>()) {
+            visit(ps, "transition");
+        } else if (auto *act = d->to<IR::P4Action>()) {
+            visit(act, "actions");
+        } else {
+            auto *obj = d->getNode();  // FIXME -- should be able to visit an INode
+            visit(obj);
+        }
+    }
+
+    bool preorder(const IR::PathExpression *path) {
+        visit_def(path);
+        return true;
+    }
+
+    MultiVisitInspector(const MultiVisitInspector &) = default;
+};
+
+struct MultiVisitModifier : public Modifier,
+                            // protected ControlFlowVisitor,
+                            virtual public P4::ResolutionContext {
+    MultiVisitModifier() { visitDagOnce = false; }
+
+ private:
+    // ignore parser and declaration loops for now
+    void loop_revisit(const IR::ParserState *) override {}
+
+    void visit_def(const IR::PathExpression *pe) {
+        auto *d = resolveUnique(pe->path->name, P4::ResolutionType::Any);
+        BUG_CHECK(d, "failed to resolve %s", pe);
+        if (auto *ps = d->to<IR::ParserState>()) {
+            visit(ps, "transition");
+        } else if (auto *act = d->to<IR::P4Action>()) {
+            visit(act, "actions");
+        } else {
+            auto *obj = d->getNode();  // FIXME -- should be able to visit an INode
+            visit(obj);
+        }
+    }
+
+    bool preorder(IR::PathExpression *path) {
+        visit_def(path);
+        return true;
+    }
+
+    MultiVisitModifier(const MultiVisitModifier &) = default;
+};
+
+std::string getMultiVisitLoopSource() {
+    // Non-sensical parser with loops
+    return R"(
+        extern packet_in {
+            void extract<T> (out T hdr);
+        }
+
+        header Header {
+            bit<32> data;
+        }
+
+        struct H {
+            Header h1;
+            Header h2;
+        }
+
+        struct M { }
+
+        parser MyParser(packet_in pkt, out H hdr, out M meta) {
+            state start {
+                transition next;
+            }
+
+            state next {
+                transition select (hdr.h1.data) {
+                    0: state0;
+                    1: state1;
+                    default: accept;
+                }
+            }
+
+            state state0 {
+                hdr.h1.setInvalid();
+                transition select (hdr.h2.data) {
+                    2: state1;
+                    default: next;
+                }
+            }
+
+            state state1 {
+                hdr.h2.setValid();
+                transition select (hdr.h2.data) {
+                    1: state1;
+                    2: state0;
+                    default: accept;
+                }
+            }
+
+            state accept { }
+        }
+    )";
+}
+
+// This test fails when Visitor::Tracker::try_start does _not_ reset done on a previously-visited
+// node
+TEST_F(P4CVisitor, MultiVisitInspectorLoop) {
+    auto *program =
+        P4::parseP4String(getMultiVisitLoopSource(), CompilerOptions::FrontendVersion::P4_16);
+    ASSERT_TRUE(program != nullptr);
+
+    program = program->apply(MultiVisitInspector());
+    ASSERT_TRUE(program != nullptr);
+}
+
+// This test fails when Visitor::ChangeTracker::try_start does _not_ reset visit_in_progress on a
+// previously-visited node
+TEST_F(P4CVisitor, MultiVisitModifierLoop) {
+    auto *program =
+        P4::parseP4String(getMultiVisitLoopSource(), CompilerOptions::FrontendVersion::P4_16);
+    ASSERT_TRUE(program != nullptr);
+
+    program = program->apply(MultiVisitModifier());
+    ASSERT_TRUE(program != nullptr);
+}
+
+}  // namespace Test