Tables cannot be compared (#3590)

Signed-off-by: Mihai Budiu <[email protected]>

frontends/p4/typeChecking/typeChecker.cpp

@@ -1727,7 +1727,7 @@ const IR::Node* TypeInference::postorder(IR::BoolLiteral* expression) {
     return expression;
 }
 
-// Returns nullptr on error
+// Returns false on error
 bool TypeInference::compare(const IR::Node* errorPosition,
                             const IR::Type* ltype,
                             const IR::Type* rtype,
@@ -1737,6 +1737,10 @@ bool TypeInference::compare(const IR::Node* errorPosition,
         typeError("%1%: cannot be applied to action results", errorPosition);
         return false;
     }
+    if (ltype->is<IR::Type_Table>() || rtype->is<IR::Type_Table>()) {
+        typeError("%1%: tables cannot be compared", errorPosition);
+        return false;
+    }
 
     bool defined = false;
     if (typeMap->equivalent(ltype, rtype) &&

testdata/p4_16_errors/issue3589.p4

@@ -0,0 +1,24 @@
+action NoAction(){}
+control eq0()
+{
+  table t {
+    actions = {NoAction;}
+  }
+  apply {
+    bool b = t == t; // { dg-error "" }
+  }
+}
+control ne0()
+{
+  table t {
+    actions = {NoAction;}
+  }
+  apply {
+    bool b = t != t; // { dg-error "" }
+  }
+}
+
+control c();
+
+package top(c c1, c c2);
+top(eq0(), ne0()) main;

testdata/p4_16_errors_outputs/issue3589.p4

@@ -0,0 +1,28 @@
+action NoAction() {
+}
+control eq0() {
+    table t {
+        actions = {
+            NoAction;
+        }
+    }
+    apply {
+        bool b = t == t;
+    }
+}
+
+control ne0() {
+    table t {
+        actions = {
+            NoAction;
+        }
+    }
+    apply {
+        bool b = t != t;
+    }
+}
+
+control c();
+package top(c c1, c c2);
+top(eq0(), ne0()) main;
+

testdata/p4_16_errors_outputs/issue3589.p4-stderr

@@ -0,0 +1,6 @@
+issue3589.p4(8): [--Werror=type-error] error: ==: tables cannot be compared
+    bool b = t == t; // { dg-error "" }
+             ^^^^^^
+issue3589.p4(17): [--Werror=type-error] error: !=: tables cannot be compared
+    bool b = t != t; // { dg-error "" }
+             ^^^^^^