[coroutines] Promote cleanup.dest.slot allocas to registers to avoid storing it in the coroutine frame

Summary:
We don't want to store cleanup dest slot saved into the coroutine frame (as some of the cleanup code may
access them after coroutine frame destroyed).

This is an alternative to https://reviews.llvm.org/D37093

It is possible to do this for all functions, but, cursory check showed that in -O0, we get slightly longer function (by 1-3 instructions), thus, we are only limiting cleanup.dest.slot elimination to coroutines.

Reviewers: rjmccall, hfinkel, eric_niebler

Reviewed By: eric_niebler

Subscribers: EricWF, cfe-commits

Differential Revision: https://reviews.llvm.org/D39768

llvm-svn: 317981

1 files changed, 26 insertions, 0 deletions

diff --git a/clang/test/CodeGenCoroutines/coro-dest-slot.cpp b/clang/test/CodeGenCoroutines/coro-dest-slot.cpp
new file mode 100644
index 00000000000..4c7395ba608
--- /dev/null
+++ b/clang/test/CodeGenCoroutines/coro-dest-slot.cpp
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcoroutines-ts -std=c++14 -emit-llvm %s -o - -disable-llvm-passes | FileCheck %s
+
+#include "Inputs/coroutine.h"
+
+using namespace std::experimental;
+
+struct coro {
+  struct promise_type {
+    coro get_return_object();
+    suspend_always initial_suspend();
+    suspend_never final_suspend();
+    void return_void();
+    static void unhandled_exception();
+  };
+};
+
+extern "C" coro f(int) { co_return; }
+// Verify that cleanup.dest.slot is eliminated in a coroutine.
+// CHECK-LABEL: f(
+// CHECK: call void @_ZNSt12experimental13coroutines_v113suspend_never12await_resumeEv(
+// CHECK: %[[CLEANUP_DEST:.+]] = phi i32 [ 0, %{{.+}} ], [ 2, %{{.+}} ], [ 2, %{{.+}} ]
+// CHECK: call i8* @llvm.coro.free(
+// CHECK: switch i32 %cleanup.dest.slot.0, label %{{.+}} [
+// CHECK-NEXT: i32 0
+// CHECK-NEXT: i32 2
+// CHECK-NEXT: ]