[coroutines] Add __builtin_coro_noop => llvm.coro.noop

A recent addition to Coroutines TS (https://wg21.link/p0913) adds a pre-defined
coroutine noop_coroutine that does nothing. To implement this feature, we implemented
an llvm.coro.noop intrinsic that returns a coroutine handle to a coroutine that
does nothing when resumed or destroyed.

This patch adds a builtin __builtin_coro_noop() that maps to llvm.coro.noop intrinsic.

Related llvm change: https://reviews.llvm.org/D45114

llvm-svn: 328993

clang/include/clang/Basic/Builtins.def

@@ -1391,6 +1391,7 @@ BUILTIN(__builtin_coro_promise, "v*v*IiIb", "n")
 
 BUILTIN(__builtin_coro_size, "z", "n")
 BUILTIN(__builtin_coro_frame, "v*", "n")
+BUILTIN(__builtin_coro_noop, "v*", "n")
 BUILTIN(__builtin_coro_free, "v*v*", "n")
 
 BUILTIN(__builtin_coro_id, "v*Iiv*v*v*", "n")

clang/lib/CodeGen/CGBuiltin.cpp

@@ -2796,6 +2796,8 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
     return EmitCoroutineIntrinsic(E, Intrinsic::coro_resume);
   case Builtin::BI__builtin_coro_frame:
     return EmitCoroutineIntrinsic(E, Intrinsic::coro_frame);
+  case Builtin::BI__builtin_coro_noop:
+    return EmitCoroutineIntrinsic(E, Intrinsic::coro_noop);
   case Builtin::BI__builtin_coro_free:
     return EmitCoroutineIntrinsic(E, Intrinsic::coro_free);
   case Builtin::BI__builtin_coro_destroy:

clang/test/CodeGenCoroutines/coro-builtins.c

@@ -17,6 +17,9 @@ void f(int n) {
   // CHECK-NEXT: call i1 @llvm.coro.alloc(token %[[COROID]])
   __builtin_coro_alloc();
 
+  // CHECK-NEXT: call i8* @llvm.coro.noop()
+  __builtin_coro_noop();
+
   // CHECK-NEXT: %[[SIZE:.+]] = call i64 @llvm.coro.size.i64()
   // CHECK-NEXT: %[[MEM:.+]] = call i8* @myAlloc(i64 %[[SIZE]])
   // CHECK-NEXT: %[[FRAME:.+]] = call i8* @llvm.coro.begin(token %[[COROID]], i8* %[[MEM]])