[CoroutineAccessors] Adopt ret.popless intrinsic.

And annotate it musttail.

Author: nate-chandler

lib/IRGen/GenCall.cpp

@@ -5149,9 +5149,10 @@ static llvm::Constant *getCoroAllocWrapperFn(IRGenModule &IGM) {
         auto *alloca =
             IGF.Builder.IRBuilderBase::CreateAlloca(IGF.IGM.Int8Ty, size);
         alloca->setAlignment(llvm::Align(MaximumAlignment));
-        auto *ret = IGF.Builder.CreateIntrinsic(
-            alloca->getType(), llvm::Intrinsic::coro_return, {alloca});
-        IGF.Builder.CreateRet(ret);
+        auto *retPopless = IGF.Builder.CreateIntrinsic(
+            IGF.IGM.VoidTy, llvm::Intrinsic::ret_popless, {});
+        retPopless->setTailCallKind(llvm::CallInst::TailCallKind::TCK_MustTail);
+        IGF.Builder.CreateRet(alloca);
         IGF.Builder.emitBlock(normalReturn);
         auto *call = IGF.Builder.CreateCall(
             IGF.IGM.getCoroAllocFunctionPointer(), {allocator, size});

test/IRGen/coroutine_accessors_popless.swift

@@ -0,0 +1,40 @@
+// RUN: %target-swift-emit-irgen                                            \
+// RUN:     %s                                                              \
+// RUN:     -enable-experimental-feature CoroutineAccessors                 \
+// RUN:     -enable-arm64-corocc                                            \
+// RUN:     -enable-x86_64-corocc                                           \
+// RUN: | %IRGenFileCheck %s
+
+// REQUIRES: CPU=arm64 || CPU=arm64e || CPU=x86_64
+// REQUIRES: swift_feature_CoroutineAccessors
+
+// CHECK-LABEL: @__swift_coro_alloc_(
+// CHECK-SAME:      ptr [[ALLOCATOR:%[^,]+]]
+// CHECK-SAME:      i64 [[SIZE:%[^)]+]]
+// CHECK-SAME:  )
+// CHECK-SAME:  {
+// CHECK:       entry:
+// CHECK:         [[USE_POPLESS:%[^,]+]] = icmp eq ptr [[ALLOCATOR]], null
+// CHECK:         br i1 [[USE_POPLESS]], 
+// CHECK-SAME:        label %coro.return.popless
+// CHECK-SAME:        label %coro.return.normal
+// CHECK:       coro.return.popless:
+// CHECK:         [[STACK_ALLOCATION:%[^,]+]] = alloca i8, i64 [[SIZE]], align 16
+// CHECK:         musttail call void @llvm.ret.popless()
+// CHECK:         ret ptr [[STACK_ALLOCATION]]
+// CHECK:       coro.return.normal:
+// CHECK:         [[OTHER_ALLOCATION:%[^,]+]] = call swiftcc ptr @swift_coro_alloc(
+// CHECK-SAME:        ptr [[ALLOCATOR]]
+// CHECK-SAME:        i64 [[SIZE]]
+// CHECK-SAME:    )
+// CHECK:         ret ptr [[OTHER_ALLOCATION]]
+// CHECK:       }
+
+public var _i: Int = 0
+
+public var i: Int {
+  read {
+    yield _i
+  }
+}
+