Add a couple convenience APIs for working with abstraction patterns

Author: rjmccall

include/swift/SIL/AbstractionPattern.h

@@ -18,6 +18,7 @@
 #ifndef SWIFT_SIL_ABSTRACTIONPATTERN_H
 #define SWIFT_SIL_ABSTRACTIONPATTERN_H
 
+#include "swift/Basic/IndexedViewRange.h"
 #include "swift/AST/Decl.h"
 #include "swift/AST/Types.h"
 
@@ -1332,6 +1333,17 @@ class AbstractionPattern {
     llvm_unreachable("bad kind");
   }
 
+  static AbstractionPattern
+  projectTupleElementType(const AbstractionPattern *base, size_t index) {
+    return base->getTupleElementType(index);
+  }
+
+  IndexedViewRange<const AbstractionPattern *, AbstractionPattern,
+                   projectTupleElementType> getTupleElementTypes() const {
+    assert(isTuple());
+    return { { this, 0 }, { this, getNumTupleElements() } };
+  }
+
   /// Is the given pack type a valid substitution of this abstraction
   /// pattern?
   bool matchesPack(CanPackType substType);
@@ -1472,6 +1484,8 @@ class AbstractionPattern {
   void forEachPackExpandedComponent(
       llvm::function_ref<void(AbstractionPattern pattern)> fn) const;
 
+  SmallVector<AbstractionPattern, 4> getPackExpandedComponents() const;
+
   /// If this pattern refers to a foreign ObjC method that was imported as 
   /// async, return the bridged-back-to-ObjC completion handler type.
   CanType getObjCMethodAsyncCompletionHandlerForeignType(

lib/SIL/IR/AbstractionPattern.cpp

@@ -588,6 +588,15 @@ AbstractionPattern AbstractionPattern::getPackExpansionCountType() const {
   llvm_unreachable("bad kind");
 }
 
+SmallVector<AbstractionPattern, 4>
+AbstractionPattern::getPackExpandedComponents() const {
+  SmallVector<AbstractionPattern, 4> result;
+  forEachPackExpandedComponent([&](AbstractionPattern pattern) {
+    result.push_back(pattern);
+  });
+  return result;
+}
+
 void AbstractionPattern::forEachPackExpandedComponent(
           llvm::function_ref<void (AbstractionPattern)> fn) const {
   assert(isPackExpansion());

lib/SILGen/SILGenApply.cpp

@@ -3229,11 +3229,8 @@ class ArgEmitter {
 
       // Otherwise we need to emit a pack argument.
       } else {
-        SmallVector<AbstractionPattern, 4> origPackEltPatterns;
-        origFormalParamType.forEachPackExpandedComponent(
-                              [&](AbstractionPattern pattern) {
-          origPackEltPatterns.push_back(pattern);
-        });
+        auto origPackEltPatterns =
+          origFormalParamType.getPackExpandedComponents();
 
         auto argSourcesSlice =
           argSources.slice(nextArgSourceIndex, origPackEltPatterns.size());

lib/SILGen/SILGenStmt.cpp

@@ -504,11 +504,7 @@ preparePackResultInit(SILGenFunction &SGF, SILLocation loc,
                       SmallVectorImpl<CleanupHandle> &cleanups,
                       SmallVectorImpl<InitializationPtr> &inits) {
   assert(origExpansionType.isPackExpansion());
-  SmallVector<AbstractionPattern, 4> origComponentTypes;
-  origExpansionType.forEachPackExpandedComponent(
-      [&](AbstractionPattern component) {
-    origComponentTypes.push_back(component);
-  });
+  auto origComponentTypes = origExpansionType.getPackExpandedComponents();
 
   auto loweredPackType = packAddr->getType().castTo<SILPackType>();
   assert(loweredPackType->getNumElements() == origComponentTypes.size() &&