Not all Type_InfInt are the same - keep track of ones that need to be unified

frontends/p4/typeChecking/typeChecker.cpp

@@ -51,10 +51,13 @@ class ConstantTypeSubstitution : public Transform {
         auto cstType = typeMap->getType(getOriginal(), true);
         if (!cstType->is<IR::ITypeVar>()) return cst;
         auto repl = cstType;
-        while (repl != nullptr && repl->is<IR::ITypeVar>())
-            repl = subst->get(repl->to<IR::ITypeVar>());
-        if (repl != nullptr && !repl->is<IR::ITypeVar>()) {
-            // maybe the substitution could not infer a width...
+        while (repl->is<IR::ITypeVar>()) {
+            auto next = subst->get(repl->to<IR::ITypeVar>());
+            if (!next) break;
+            repl = next;
+        }
+        if (repl != cstType) {
+            // We may replace a type variable with another one
             LOG2("Inferred type " << repl << " for " << cst);
             cst = new IR::Constant(cst->srcInfo, repl, cst->value, cst->base);
         } else {
@@ -2118,7 +2121,7 @@ const IR::Node* TypeInference::postorder(IR::P4ListExpression* expression) {
             ConstantTypeSubstitution cts(tvs, refMap, typeMap, this);
             auto converted = cts.convert(c);
             vec->push_back(converted);
-            changed = true;
+            changed = changed || converted != c;
         } else {
             vec->push_back(c);
         }

frontends/p4/typeChecking/typeConstraints.cpp

@@ -38,7 +38,7 @@ TypeVariableSubstitution* TypeConstraints::solve() {
         if (!success) return nullptr;
     }
     LOG3("Constraint solution:\n" << currentSubstitution);
-    return currentSubstitution->trim();
+    return currentSubstitution;
 }
 
 bool TypeConstraints::isUnifiableTypeVariable(const IR::Type* type) {

frontends/p4/typeChecking/typeSubstitution.cpp

@@ -110,15 +110,6 @@ bool TypeVariableSubstitution::setBindings(const IR::Node* errorLocation,
     return true;
 }
 
-TypeVariableSubstitution* TypeVariableSubstitution::trim() const {
-    TypeVariableSubstitution* result = new TypeVariableSubstitution();
-    for (auto it : binding) {
-        if (it.first->is<IR::Type_InfInt>() && it.second->is<IR::Type_InfInt>()) continue;
-        result->setBinding(it.first, it.second);
-    }
-    return result;
-}
-
 // to call from gdb
 void dump(P4::TypeVariableSubstitution& tvs) { std::cout << tvs << std::endl; }
 void dump(P4::TypeVariableSubstitution* tvs) { std::cout << *tvs << std::endl; }

frontends/p4/typeChecking/typeSubstitution.h

@@ -75,15 +75,13 @@ class TypeVariableSubstitution final : public TypeSubstitution<const IR::ITypeVa
     TypeVariableSubstitution(const TypeVariableSubstitution& other) = default;
     bool setBindings(const IR::Node* errorLocation, const IR::TypeParameters* params,
                      const IR::Vector<IR::Type>* args);
-    /// Returns an empyty string on error, or an error message format otherwise.
+    /// Returns an empty string on error, or an error message format otherwise.
     /// The error message should be used with 'var' and 'substitution' as arguments when
     /// reporting an error (i.e., it may contain %1% and %2% inside).
     cstring compose(const IR::ITypeVar* var, const IR::Type* substitution);
     // In this variant of compose all variables in 'other' that are
     // assigned to are disjoint from all variables already in 'this'.
     void simpleCompose(const TypeVariableSubstitution* other);
-    // Remove substitutions of the form int->int.
-    TypeVariableSubstitution* trim() const;
 };
 
 }  // namespace P4

testdata/p4_16_samples/issue3806.p4

@@ -0,0 +1,12 @@
+header ethernet_t {
+    bit<48> dst_addr;
+    bit<48> src_addr;
+    bit<16> eth_type;
+}
+struct Headers {
+    ethernet_t eth_hdr;
+}
+
+void f (inout Headers h) {
+  h.eth_hdr = h.eth_hdr.eth_type == 1 ? {1, 1, 1} : {2, 2, 2};
+}

testdata/p4_16_samples_outputs/issue3806-first.p4

@@ -0,0 +1,13 @@
+header ethernet_t {
+    bit<48> dst_addr;
+    bit<48> src_addr;
+    bit<16> eth_type;
+}
+
+struct Headers {
+    ethernet_t eth_hdr;
+}
+
+void f(inout Headers h) {
+    h.eth_hdr = (h.eth_hdr.eth_type == 16w1 ? (ethernet_t){dst_addr = 48w1,src_addr = 48w1,eth_type = 16w1} : (ethernet_t){dst_addr = 48w2,src_addr = 48w2,eth_type = 16w2});
+}

testdata/p4_16_samples_outputs/issue3806-frontend.p4

@@ -0,0 +1,10 @@
+header ethernet_t {
+    bit<48> dst_addr;
+    bit<48> src_addr;
+    bit<16> eth_type;
+}
+
+struct Headers {
+    ethernet_t eth_hdr;
+}
+

testdata/p4_16_samples_outputs/issue3806.p4

@@ -0,0 +1,13 @@
+header ethernet_t {
+    bit<48> dst_addr;
+    bit<48> src_addr;
+    bit<16> eth_type;
+}
+
+struct Headers {
+    ethernet_t eth_hdr;
+}
+
+void f(inout Headers h) {
+    h.eth_hdr = (h.eth_hdr.eth_type == 1 ? { 1, 1, 1 } : { 2, 2, 2 });
+}

testdata/p4_16_samples_outputs/issue3806.p4-stderr

@@ -0,0 +1 @@
+[--Wwarn=missing] warning: Program does not contain a `main' module