[NFC] Store the list of opened pack parameters as a flat array in

opened generic environments

Finding these is very hot for these environments, so doing it once
is a pretty nice win in both speed and code complexity.

I'm not actually using this yet.

Author: rjmccall

include/swift/AST/GenericEnvironment.h

@@ -129,6 +129,12 @@ class alignas(1 << DeclAlignInBits) GenericEnvironment final
   /// generic signature.
   ArrayRef<Type> getContextTypes() const;
 
+  /// Retrieve the array of opened pack parameters for this opened-element
+  /// environment.  This is parallel to the array of element parameters,
+  /// i.e. the innermost generic context.
+  MutableArrayRef<Type> getOpenedPackParams();
+  ArrayRef<Type> getOpenedPackParams() const;
+
   /// Get the nested type storage, allocating it if required.
   NestedTypeStorage &getOrCreateNestedTypeStorage();
 
@@ -201,6 +207,9 @@ class alignas(1 << DeclAlignInBits) GenericEnvironment final
   /// Retrieve the UUID for an opened element environment.
   UUID getOpenedElementUUID() const;
 
+  /// Return the number of opened pack parameters.
+  unsigned getNumOpenedPackParams() const;
+
   void forEachPackElementArchetype(
           llvm::function_ref<void(ElementArchetypeType*)> function) const;
 

lib/AST/ASTContext.cpp

@@ -5164,10 +5164,12 @@ GenericEnvironment::forOpenedElement(GenericSignature signature,
 
   // Allocate and construct the new environment.
   unsigned numGenericParams = signature.getGenericParams().size();
+  unsigned numOpenedParams = signature.getInnermostGenericParams().size();
   size_t bytes = totalSizeToAlloc<OpaqueEnvironmentData,
                                   OpenedExistentialEnvironmentData,
-                                  OpenedElementEnvironmentData, Type>(
-      0, 0, 1, numGenericParams);
+                                  OpenedElementEnvironmentData,
+                                  Type>(
+      0, 0, 1, numGenericParams + numOpenedParams);
   void *mem = ctx.Allocate(bytes, alignof(GenericEnvironment));
   auto *genericEnv = new (mem) GenericEnvironment(signature,
                                                   uuid, shapeClass,

lib/AST/GenericEnvironment.cpp

@@ -63,7 +63,8 @@ size_t GenericEnvironment::numTrailingObjects(
 }
 
 size_t GenericEnvironment::numTrailingObjects(OverloadToken<Type>) const {
-  return getGenericParams().size();
+  return getGenericParams().size()
+       + (getKind() == Kind::OpenedElement ? getNumOpenedPackParams() : 0);
 }
 
 /// Retrieve the array containing the context types associated with the
@@ -82,6 +83,21 @@ ArrayRef<Type> GenericEnvironment::getContextTypes() const {
                         getGenericParams().size());
 }
 
+unsigned GenericEnvironment::getNumOpenedPackParams() const {
+  assert(getKind() == Kind::OpenedElement);
+  return getGenericSignature().getInnermostGenericParams().size();
+}
+
+MutableArrayRef<Type> GenericEnvironment::getOpenedPackParams() {
+  auto begin = getTrailingObjects<Type>() + getGenericParams().size();
+  return MutableArrayRef<Type>(begin, getNumOpenedPackParams());
+}
+
+ArrayRef<Type> GenericEnvironment::getOpenedPackParams() const {
+  auto begin = getTrailingObjects<Type>() + getGenericParams().size();
+  return ArrayRef<Type>(begin, getNumOpenedPackParams());
+}
+
 TypeArrayView<GenericTypeParamType>
 GenericEnvironment::getGenericParams() const {
   return getGenericSignature().getGenericParams();
@@ -230,6 +246,16 @@ GenericEnvironment::GenericEnvironment(GenericSignature signature,
   // Clear out the memory that holds the context types.
   std::uninitialized_fill(getContextTypes().begin(), getContextTypes().end(),
                           Type());
+
+  // Fill in the array of opened pack parameters.
+  auto openedPacksBuffer = getOpenedPackParams();
+  unsigned i = 0;
+  for (auto param : signature.getGenericParams()) {
+    if (!param->isParameterPack()) continue;
+    if (!signature->haveSameShape(param, shapeClass)) continue;
+    openedPacksBuffer[i++] = param;
+  }
+  assert(i == openedPacksBuffer.size());
 }
 
 void GenericEnvironment::addMapping(GenericParamKey key,