[GSB] Stop collapsing "structurally equivalent" potential archetypes.

Now that we only record potential archetypes involving the "anchor"
archetypes, there is no need to collapse structurally-equivalent potential
archetypes. Delete some temporary code.

Author: DougGregor

lib/AST/GenericSignatureBuilder.cpp

@@ -5504,53 +5504,6 @@ static void collapseSameTypeComponentsThroughDelayedRequirements(
                          collapsedParents.end());
 }
 
-/// Check whether two potential archetypes "structurally" match, e.g.,
-/// the names match up to the root (which must match).
-static bool potentialArchetypesStructurallyMatch(PotentialArchetype *pa1,
-                                                 PotentialArchetype *pa2) {
-  auto parent1 = pa1->getParent();
-  auto parent2 = pa2->getParent();
-  if (!parent1 && !parent2)
-    return pa1->getGenericParamKey() == pa2->getGenericParamKey();
-
-  // Check for depth mismatch.
-  if (static_cast<bool>(parent1) != static_cast<bool>(parent2))
-    return false;
-
-  // Check names.
-  if (pa1->getNestedName() != pa2->getNestedName())
-    return false;
-
-  return potentialArchetypesStructurallyMatch(parent1, parent2);
-}
-
-/// Look for structurally-equivalent types within the given equivalence class,
-/// collapsing their components.
-static void collapseStructurallyEquivalentSameTypeComponents(
-              EquivalenceClass *equivClass,
-              llvm::SmallDenseMap<PotentialArchetype *, unsigned> &componentOf,
-              SmallVectorImpl<unsigned> &collapsedParents,
-              unsigned &remainingComponents) {
-  for (unsigned i : indices(equivClass->members)) {
-    auto pa1 = equivClass->members[i];
-    auto rep1 = findRepresentative(collapsedParents, componentOf[pa1]);
-    for (unsigned j : indices(equivClass->members).slice(i + 1)) {
-      auto pa2 = equivClass->members[j];
-      auto rep2 = findRepresentative(collapsedParents, componentOf[pa2]);
-      if (rep1 == rep2) continue;
-
-      auto depth = pa1->getNestingDepth();
-      if (depth < 2 || depth != pa2->getNestingDepth()) continue;
-
-      if (potentialArchetypesStructurallyMatch(pa1, pa2) &&
-          unionSets(collapsedParents, rep1, rep2)) {
-        --remainingComponents;
-        rep1 = findRepresentative(collapsedParents, componentOf[pa1]);
-      }
-    }
-  }
-}
-
 /// Collapse same-type components within an equivalence class, minimizing the
 /// number of requirements required to express the equivalence class.
 static void collapseSameTypeComponents(
@@ -5611,14 +5564,6 @@ static void collapseSameTypeComponents(
       builder, equivClass, componentOf, collapsedParents, remainingComponents);
   }
 
-  if (remainingComponents > 1) {
-    // Collapse structurally-equivalent components.
-    collapseStructurallyEquivalentSameTypeComponents(equivClass,
-                                                     componentOf,
-                                                     collapsedParents,
-                                                     remainingComponents);
-  }
-
   // If needed, collapse the same-type components merged by a derived
   // nested-type-name-match edge.
   unsigned maxComponents = equivClass->derivedSameTypeComponents.size();

test/IRGen/associated_types.swift

@@ -66,11 +66,12 @@ protocol FastRuncible {
 // information for archetypes from all paths to that archetype, not just
 // its parent relationships.
 
-func testFastRuncible<T: Runcible, U: FastRuncible where T.RuncerType == U.RuncerType>(_ t: T, u: U) {
+func testFastRuncible<T: Runcible, U: FastRuncible>(_ t: T, u: U)
+   where T.RuncerType == U.RuncerType {
   U.RuncerType.Runcee.accelerate()
 }
 
-// CHECK: define hidden swiftcc void @_T016associated_types16testFastRuncibleyx_q_1utAA0E0RzAA0dE0R_10RuncerTypeQy_AFRtzr0_lF(%swift.opaque* noalias nocapture, %swift.opaque* noalias nocapture, %swift.type* %T, %swift.type* %U, i8** %T.Runcible, i8** %U.FastRuncible) #0 {
+// CHECK: define hidden swiftcc void @_T016associated_types16testFastRuncibleyx_q_1utAA0E0RzAA0dE0R_10RuncerTypeQy_AFRtzAF_6RunceeAA0F0PQZAF_AiA0dF0PRTzr0_lF(%swift.opaque* noalias nocapture, %swift.opaque* noalias nocapture, %swift.type* %T, %swift.type* %U, i8** %T.Runcible, i8** %U.FastRuncible) #0 {
 //   1. Get the type metadata for U.RuncerType.Runcee.
 //     1a. Get the type metadata for U.RuncerType.
 //         Note that we actually look things up in T, which is going to prove unfortunate.