RequirementMachine: Fold RewriteSystem::processConflicts() into recordConflict() and add debug output

Author: slavapestov

lib/AST/RequirementMachine/Debug.h

@@ -72,6 +72,9 @@ enum class DebugFlags : unsigned {
 
   /// Print a trace of requirement machines constructed and how long each took.
   Timers = (1<<16),
+
+  /// Print conflicting rules.
+  ConflictingRules = (1<<17),
 };
 
 using DebugOptions = OptionSet<DebugFlags>;

lib/AST/RequirementMachine/HomotopyReduction.cpp

@@ -167,30 +167,6 @@ void RewriteSystem::propagateRedundantRequirementIDs() {
   }
 }
 
-/// Process pairs of conflicting rules, marking the more specific rule as
-/// conflicting, which instructs minimization to drop this rule.
-void RewriteSystem::processConflicts() {
-  for (auto pair : ConflictingRules) {
-    auto *existingRule = &getRule(pair.first);
-    auto *newRule = &getRule(pair.second);
-
-    // The identity conformance rule ([P].[P] => [P]) will conflict with
-    // a concrete type requirement in an invalid protocol declaration
-    // where 'Self' is constrained to a type that does not conform to
-    // the protocol. This rule is permanent, so don't mark it as
-    // conflicting in this case.
-
-    if (!existingRule->isIdentityConformanceRule() &&
-        existingRule->getRHS().size() >= newRule->getRHS().size())
-      existingRule->markConflicting();
-    if (!newRule->isIdentityConformanceRule() &&
-        newRule->getRHS().size() >= existingRule->getRHS().size())
-      newRule->markConflicting();
-
-    // FIXME: Diagnose the conflict later.
-  }
-}
-
 /// Find a rule to delete by looking through all loops for rewrite rules appearing
 /// once in empty context. Returns a pair consisting of a loop ID and a rule ID,
 /// otherwise returns None.
@@ -477,7 +453,6 @@ void RewriteSystem::minimizeRewriteSystem() {
   Minimized = 1;
 
   propagateExplicitBits();
-  processConflicts();
 
   if (Context.getASTContext().LangOpts.EnableRequirementMachineLoopNormalization) {
     for (auto &loop : Loops) {

lib/AST/RequirementMachine/PropertyUnification.cpp

@@ -119,9 +119,37 @@ static void recordRelation(Term key,
   (void) system.addRule(lhs, rhs, &path);
 }
 
+/// Given two property rules that conflict because no concrete type
+/// can satisfy both, mark one or both rules conflicting.
+///
+/// The right hand side of one rule must be a suffix of the other
+/// (in which case the longer of the two rules is conflicting) or
+/// the right hand sides are equal (in which case both will be
+/// conflicting).
 void RewriteSystem::recordConflict(unsigned existingRuleID,
                                    unsigned newRuleID) {
   ConflictingRules.emplace_back(existingRuleID, newRuleID);
+
+  auto &existingRule = getRule(existingRuleID);
+  auto &newRule = getRule(newRuleID);
+
+  if (Debug.contains(DebugFlags::ConflictingRules)) {
+    llvm::dbgs() << "Conflicting rules:\n";
+    llvm::dbgs() << "- " << existingRule << "\n";
+    llvm::dbgs() << "- " << newRule << "\n";
+  }
+
+  // The identity conformance rule ([P].[P] => [P]) will conflict with
+  // a concrete type requirement in an invalid protocol declaration
+  // where 'Self' is constrained to a type that does not conform to
+  // the protocol. This rule is permanent, so don't mark it as
+  // conflicting in this case.
+  if (!existingRule.isIdentityConformanceRule() &&
+      existingRule.getRHS().size() >= newRule.getRHS().size())
+    existingRule.markConflicting();
+  if (!newRule.isIdentityConformanceRule() &&
+      newRule.getRHS().size() >= existingRule.getRHS().size())
+    newRule.markConflicting();
 }
 
 void PropertyMap::addConformanceProperty(

lib/AST/RequirementMachine/RewriteContext.cpp

@@ -177,6 +177,7 @@ static DebugOptions parseDebugFlags(StringRef debugFlags) {
       .Case("concrete-contraction", DebugFlags::ConcreteContraction)
       .Case("propagate-requirement-ids", DebugFlags::PropagateRequirementIDs)
       .Case("timers", DebugFlags::Timers)
+      .Case("conflicting-rules", DebugFlags::ConflictingRules)
       .Default(None);
     if (!flag) {
       llvm::errs() << "Unknown debug flag in -debug-requirement-machine "

lib/AST/RequirementMachine/RewriteSystem.h

@@ -361,8 +361,6 @@ class RewriteSystem final {
 
   void propagateRedundantRequirementIDs();
 
-  void processConflicts();
-
   using EliminationPredicate = llvm::function_ref<bool(unsigned loopID,
                                                        unsigned ruleID)>;