[Async CC] Move self after formal arguments.

Partial applies of methods supply only self.  When applies of the
resulting thick function are performed, that self was one of the
arguments is not known.  As a result, self must appear after the fields
that might be supplied at the apply site, which  is to say all the
arguments.

Author: nate-chandler

lib/IRGen/GenCall.cpp

@@ -143,29 +143,6 @@ AsyncContextLayout irgen::getAsyncContextLayout(
   if (hasLocalContextParameter) {
     parameters = parameters.drop_back();
   }
-  Optional<AsyncContextLayout::ArgumentInfo> localContextInfo = llvm::None;
-  if (hasLocalContext) {
-    if (hasLocalContextParameter) {
-      SILType ty =
-          IGF.IGM.silConv.getSILType(localContextParameter, substitutedType,
-                                     IGF.IGM.getMaximalTypeExpansionContext());
-      auto argumentLoweringType =
-          getArgumentLoweringType(ty.getASTType(), localContextParameter,
-                                  /*isNoEscape*/ true);
-
-      auto &ti = IGF.getTypeInfoForLowered(argumentLoweringType);
-      valTypes.push_back(ty);
-      typeInfos.push_back(&ti);
-      localContextInfo = {ty, localContextParameter.getConvention()};
-    } else {
-      // TODO: DETERMINE: Is there a field in this case to match the sync ABI?
-      auto &ti = IGF.IGM.getNativeObjectTypeInfo();
-      SILType ty = SILType::getNativeObjectType(IGF.IGM.Context);
-      valTypes.push_back(ty);
-      typeInfos.push_back(&ti);
-      localContextInfo = {ty, substitutedType->getCalleeConvention()};
-    }
-  }
 
   //   ArgTypes formalArguments...;
   for (auto parameter : parameters) {
@@ -192,6 +169,31 @@ AsyncContextLayout irgen::getAsyncContextLayout(
     typeInfos.push_back(&bindingsTI);
   }
 
+  Optional<AsyncContextLayout::ArgumentInfo> localContextInfo = llvm::None;
+  if (hasLocalContext) {
+    if (hasLocalContextParameter) {
+      SILType ty =
+          IGF.IGM.silConv.getSILType(localContextParameter, substitutedType,
+                                     IGF.IGM.getMaximalTypeExpansionContext());
+      auto argumentLoweringType =
+          getArgumentLoweringType(ty.getASTType(), localContextParameter,
+                                  /*isNoEscape*/ true);
+
+      auto &ti = IGF.getTypeInfoForLowered(argumentLoweringType);
+      valTypes.push_back(ty);
+      typeInfos.push_back(&ti);
+      localContextInfo = {ty, localContextParameter.getConvention()};
+    } else {
+      // TODO: DETERMINE: Is there a field in this case to match the sync ABI?
+      auto &ti = IGF.IGM.getNativeObjectTypeInfo();
+      SILType ty = SILType::getNativeObjectType(IGF.IGM.Context);
+      valTypes.push_back(ty);
+      typeInfos.push_back(&ti);
+      localContextInfo = {ty, substitutedType->getCalleeConvention()};
+    }
+  }
+
+
   Optional<AsyncContextLayout::TrailingWitnessInfo> trailingWitnessInfo;
   if (originalType->getRepresentation() ==
       SILFunctionTypeRepresentation::WitnessMethod) {

lib/IRGen/GenCall.h

@@ -83,6 +83,8 @@ namespace irgen {
   //     };
   //     ResultTypes directResults...;
   //   };
+  //   ArgTypes formalArguments...;
+  //   SelfType self?;
   // };
   struct AsyncContextLayout : StructLayout {
     struct ArgumentInfo {
@@ -124,14 +126,7 @@ namespace irgen {
     unsigned getIndexAfterDirectReturns() {
       return getFirstDirectReturnIndex() + getDirectReturnCount();
     }
-    unsigned getLocalContextIndex() {
-      assert(hasLocalContext());
-      return getIndexAfterDirectReturns();
-    }
-    unsigned getIndexAfterLocalContext() {
-      return getIndexAfterDirectReturns() + (hasLocalContext() ? 1 : 0);
-    }
-    unsigned getFirstArgumentIndex() { return getIndexAfterLocalContext(); }
+    unsigned getFirstArgumentIndex() { return getIndexAfterDirectReturns(); }
     unsigned getIndexAfterArguments() {
       return getFirstArgumentIndex() + getArgumentCount();
     }
@@ -142,16 +137,24 @@ namespace irgen {
     unsigned getIndexAfterBindings() {
       return getIndexAfterArguments() + (hasBindings() ? 1 : 0);
     }
+    unsigned getLocalContextIndex() {
+      assert(hasLocalContext());
+      return getIndexAfterBindings();
+    }
+    unsigned getIndexAfterLocalContext() {
+      return getIndexAfterBindings() +
+             (hasLocalContext() ? 1 : 0);
+    }
     unsigned getSelfMetadataIndex() {
       assert(hasTrailingWitnesses());
-      return getIndexAfterBindings();
+      return getIndexAfterLocalContext();
     }
     unsigned getSelfWitnessTableIndex() {
       assert(hasTrailingWitnesses());
-      return getIndexAfterBindings() + 1;
+      return getIndexAfterLocalContext() + 1;
     }
     unsigned getIndexAfterTrailingWitnesses() {
-      return getIndexAfterBindings() + (hasTrailingWitnesses() ? 2 : 0);
+      return getIndexAfterLocalContext() + (hasTrailingWitnesses() ? 2 : 0);
     }
 
   public: