[coroutines] Add DependentCoawaitExpr and fix re-building CoroutineBodyStmt.

Summary:
The changes contained in this patch are:

1. Defines a new AST node `CoawaitDependentExpr` for representing co_await expressions while the promise type is still dependent.
2. Correctly detect and transform the 'co_await' operand to  `p.await_transform(<expr>)`  when possible.
3. Change the initial/final suspend points to build during the initial parse, so they have the correct operator co_await lookup results.
4.  Fix transformation of the CoroutineBodyStmt so that it doesn't re-build the final/initial suspends.


@rsmith: This change is a little big, but it's not trivial for me to split it up. Please let me know if you would prefer this submitted as multiple patches.



Reviewers: rsmith, GorNishanov

Reviewed By: rsmith

Subscribers: ABataev, rsmith, mehdi_amini, cfe-commits

Differential Revision: https://reviews.llvm.org/D26057

llvm-svn: 297093

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/AST/StmtPrinter.cpp b/clang/lib/AST/StmtPrinter.cpp
index 1ba1aa40ec5..21f5259c3ca 100644
--- a/clang/lib/AST/StmtPrinter.cpp
+++ b/clang/lib/AST/StmtPrinter.cpp
@@ -2475,6 +2475,13 @@ void StmtPrinter::VisitCoawaitExpr(CoawaitExpr *S) {
   PrintExpr(S->getOperand());
 }
 
+
+void StmtPrinter::VisitDependentCoawaitExpr(DependentCoawaitExpr *S) {
+  OS << "co_await ";
+  PrintExpr(S->getOperand());
+}
+
+
 void StmtPrinter::VisitCoyieldExpr(CoyieldExpr *S) {
   OS << "co_yield ";
   PrintExpr(S->getOperand());