RequirementMachine: Implement GenericSignature::getLayoutConstraint() query

Author: slavapestov

include/swift/AST/RequirementMachine.h

@@ -20,6 +20,7 @@ class AssociatedTypeDecl;
 class CanGenericSignature;
 class CanType;
 class GenericSignature;
+class LayoutConstraint;
 class ProtocolDecl;
 class Requirement;
 class Type;
@@ -50,6 +51,7 @@ class RequirementMachine final {
   ~RequirementMachine();
 
   bool requiresClass(Type depType) const;
+  LayoutConstraint getLayoutConstraint(Type depType) const;
   bool requiresProtocol(Type depType, const ProtocolDecl *proto) const;
 };
 

lib/AST/GenericSignature.cpp

@@ -452,14 +452,44 @@ LayoutConstraint GenericSignatureImpl::getLayoutConstraint(Type type) const {
   assert(type->isTypeParameter() &&
          "Only type parameters can have layout constraints");
 
-  auto &builder = *getGenericSignatureBuilder();
-  auto equivClass =
-    builder.resolveEquivalenceClass(
-                                  type,
-                                  ArchetypeResolutionKind::CompleteWellFormed);
-  if (!equivClass) return LayoutConstraint();
+  auto computeViaGSB = [&]() {
+    auto &builder = *getGenericSignatureBuilder();
+    auto equivClass =
+      builder.resolveEquivalenceClass(
+                                    type,
+                                    ArchetypeResolutionKind::CompleteWellFormed);
+    if (!equivClass) return LayoutConstraint();
+
+    return equivClass->layout;
+  };
+
+  auto computeViaRQM = [&]() {
+    auto *machine = getRequirementMachine();
+    return machine->getLayoutConstraint(type);
+  };
+
+  auto &ctx = getASTContext();
+  if (ctx.LangOpts.EnableRequirementMachine) {
+    auto rqmResult = computeViaRQM();
+
+#ifndef NDEBUG
+    auto gsbResult = computeViaGSB();
+
+    if (gsbResult != rqmResult) {
+      llvm::errs() << "RequirementMachine::getLayoutConstraint() is broken\n";
+      llvm::errs() << "Generic signature: " << GenericSignature(this) << "\n";
+      llvm::errs() << "Dependent type: "; type.dump(llvm::errs());
+      llvm::errs() << "\n";
+      llvm::errs() << "GenericSignatureBuilder says: " << gsbResult << "\n";
+      llvm::errs() << "RequirementMachine says: " << rqmResult << "\n";
+      abort();
+    }
+#endif
 
-  return equivClass->layout;
+    return rqmResult;
+  } else {
+    return computeViaGSB();
+  }
 }
 
 bool GenericSignatureImpl::areSameTypeParameterInContext(Type type1,

lib/AST/RequirementMachine/RequirementMachine.cpp

@@ -353,6 +353,18 @@ bool RequirementMachine::requiresClass(Type depType) const {
   return (layout && layout->isClass());
 }
 
+LayoutConstraint RequirementMachine::getLayoutConstraint(Type depType) const {
+  auto term = Impl->Context.getMutableTermForType(depType->getCanonicalType(),
+                                                  /*proto=*/nullptr);
+  Impl->System.simplify(term);
+
+  auto *equivClass = Impl->Map.lookUpEquivalenceClass(term);
+  if (!equivClass)
+    return LayoutConstraint();
+
+  return equivClass->getLayoutConstraint();
+}
+
 bool RequirementMachine::requiresProtocol(Type depType,
                                           const ProtocolDecl *proto) const {
   auto term = Impl->Context.getMutableTermForType(depType->getCanonicalType(),