Merge pull request #18032 from rudkx/restore-order

Return to the old disjunction ordering until some test regressions are addressed.

Author: rudkx

lib/Sema/CSSolver.cpp

@@ -1858,24 +1858,98 @@ static bool shouldSkipDisjunctionChoice(ConstraintSystem &cs,
   return false;
 }
 
+// Attempt to find a disjunction of bind constraints where all options
+// in the disjunction are binding the same type variable.
+//
+// Prefer disjunctions where the bound type variable is also the
+// right-hand side of a conversion constraint, since having a concrete
+// type that we're converting to can make it possible to split the
+// constraint system into multiple ones.
+static Constraint *selectBestBindingDisjunction(
+    ConstraintSystem &cs, SmallVectorImpl<Constraint *> &disjunctions) {
+
+  if (disjunctions.empty())
+    return nullptr;
+
+  // Collect any disjunctions that simply attempt bindings for a
+  // type variable.
+  SmallVector<Constraint *, 8> bindingDisjunctions;
+  for (auto *disjunction : disjunctions) {
+    llvm::Optional<TypeVariableType *> commonTypeVariable;
+    if (llvm::all_of(
+            disjunction->getNestedConstraints(),
+            [&](Constraint *bindingConstraint) {
+              if (bindingConstraint->getKind() != ConstraintKind::Bind)
+                return false;
+
+              auto *tv =
+                  bindingConstraint->getFirstType()->getAs<TypeVariableType>();
+              // Only do this for simple type variable bindings, not for
+              // bindings like: ($T1) -> $T2 bind String -> Int
+              if (!tv)
+                return false;
+
+              if (!commonTypeVariable.hasValue())
+                commonTypeVariable = tv;
+
+              if (commonTypeVariable.getValue() != tv)
+                return false;
+
+              return true;
+            })) {
+      bindingDisjunctions.push_back(disjunction);
+    }
+  }
+
+  for (auto *disjunction : bindingDisjunctions) {
+    auto nested = disjunction->getNestedConstraints();
+    assert(!nested.empty());
+    auto *tv = cs.simplifyType(nested[0]->getFirstType())
+                   ->getRValueType()
+                   ->getAs<TypeVariableType>();
+    assert(tv);
+
+    SmallVector<Constraint *, 8> constraints;
+    cs.getConstraintGraph().gatherConstraints(
+        tv, constraints, ConstraintGraph::GatheringKind::EquivalenceClass);
+
+    for (auto *constraint : constraints) {
+      if (constraint->getKind() != ConstraintKind::Conversion)
+        continue;
+
+      auto toType =
+          cs.simplifyType(constraint->getSecondType())->getRValueType();
+      auto *toTV = toType->getAs<TypeVariableType>();
+      if (tv != toTV)
+        continue;
+
+      return disjunction;
+    }
+  }
+
+  // If we had any binding disjunctions, return the first of
+  // those. These ensure that we attempt to bind types earlier than
+  // trying the elements of other disjunctions, which can often mean
+  // we fail faster.
+  if (!bindingDisjunctions.empty())
+    return bindingDisjunctions[0];
+
+  return nullptr;
+}
+
 Constraint *ConstraintSystem::selectDisjunction() {
   SmallVector<Constraint *, 4> disjunctions;
 
   collectDisjunctions(disjunctions);
+  if (auto *disjunction = selectBestBindingDisjunction(*this, disjunctions))
+    return disjunction;
 
-  // Pick the disjunction with the lowest disjunction number in order
-  // to solve them in the order they were created (which should be
-  // stable within an expression).
+  // Pick the disjunction with the smallest number of active choices.
   auto minDisjunction =
       std::min_element(disjunctions.begin(), disjunctions.end(),
                        [&](Constraint *first, Constraint *second) -> bool {
-                         auto firstFound = DisjunctionNumber.find(first);
-                         auto secondFound = DisjunctionNumber.find(second);
-
-                         assert(firstFound != DisjunctionNumber.end() &&
-                                secondFound != DisjunctionNumber.end());
-
-                         return firstFound->second < secondFound->second;
+                         return first->countActiveNestedConstraints() <
+                                second->countActiveNestedConstraints();
                        });
 
   if (minDisjunction != disjunctions.end())

validation-test/stdlib/AnyHashable.swift.gyb

@@ -757,9 +757,8 @@ AnyHashableTests.test("AnyHashable(MinimalHashableRCSwiftError)/Hashable") {
     xs,
     equalityOracle: { $0 / 2 == $1 / 2 },
     hashEqualityOracle: { $0 / 4 == $1 / 4 })
-  let mapped = xs.map(AnyHashable.init)
   checkHashable(
-    mapped,
+    xs.map(AnyHashable.init),
     equalityOracle: { $0 / 2 == $1 / 2 },
     hashEqualityOracle: { $0 / 4 == $1 / 4 })
 }