RequirementMachine: More debugging messages and a new assert

Author: slavapestov

lib/AST/RequirementMachine/SimplifySubstitutions.cpp

@@ -193,12 +193,29 @@ void RewriteSystem::processTypeDifference(const TypeDifference &difference,
                                           unsigned differenceID,
                                           unsigned lhsRuleID,
                                           const RewritePath &rhsPath) {
-  if (!CheckedDifferences.insert(differenceID).second)
-    return;
-
   bool debug = Debug.contains(DebugFlags::ConcreteUnification);
 
+  if (!CheckedDifferences.insert(differenceID).second) {
+    if (debug) {
+      llvm::dbgs() << "%% Already processed difference ID "
+                   << differenceID << "\n";
+    }
+
+    auto &lhsRule = getRule(lhsRuleID);
+    if (lhsRule.getRHS() == difference.BaseTerm &&
+        !lhsRule.isSubstitutionSimplified()) {
+      llvm::errs() << "Rule should already be subst-simplified: "
+                   << lhsRule << "\n";
+      llvm::errs() << "Difference ID: " << differenceID << "\n\n";
+      dump(llvm::errs());
+      abort();
+    }
+
+    return;
+  }
+
   if (debug) {
+    llvm::dbgs() << "%% Processing difference ID " << differenceID << "\n";
     difference.dump(llvm::dbgs());
   }
 
@@ -263,7 +280,8 @@ void RewriteSystem::processTypeDifference(const TypeDifference &difference,
       !lhsRule.isSubstitutionSimplified()) {
     if (lhsRule.isFrozen()) {
       llvm::errs() << "Frozen rule should already be subst-simplified: "
-                   << lhsRule << "\n\n";
+                   << lhsRule << "\n";
+      llvm::errs() << "Difference ID: " << differenceID << "\n\n";
       dump(llvm::errs());
       abort();
     }