[Coroutines] Set presplit attribute in Clang instead of CoroEarly pass

[lxfind]

Summary

Presplit coroutines cannot be inlined. During AlwaysInliner we check if a function is a presplit coroutine, if so we skip inlining.
The presplit coroutine attributes are set in CoroEarly pass.
However in O0 pipeline, AlwaysInliner runs before CoroEarly, so the attribute isn't set yet and will still inline the coroutine.
This causes Clang to crash: https://bugs.llvm.org/show_bug.cgi?id=49920

To fix this, we set the attributes in the Clang front-end instead of in CoroEarly pass.

[rjmccall]

Why does this pass even exist? We should just expect the frontend to set the attribute. It's not like frontends don't have to otherwise know that they're emitting a coroutine; a ton of things about the expected entire IR pattern are different.

[lxfind]

In D100282#2682251, @rjmccall wrote:

Why does this pass even exist? We should just expect the frontend to set the attribute. It's not like frontends don't have to otherwise know that they're emitting a coroutine; a ton of things about the expected entire IR pattern are different.

The attribute setting can totally be moved to the front-end.
One thing that's not clear to me is whether we should simply set coroutine functions noinline instead of replying on the attributres for this.
GCC seems to complain about inlining coroutines: https://godbolt.org/z/KrzE1znno, not fully sure why.

As for the CoroEarly pass, it lowers a bunch of intrinsics. Technically I think they can all be done in the front-end. But moving some complexity out of front-end to IR seems reasonable to me.

[rjmccall]

In D100282#2682269, @lxfind wrote:

In D100282#2682251, @rjmccall wrote:

Why does this pass even exist? We should just expect the frontend to set the attribute. It's not like frontends don't have to otherwise know that they're emitting a coroutine; a ton of things about the expected entire IR pattern are different.

The attribute setting can totally be moved to the front-end.
One thing that's not clear to me is whether we should simply set coroutine functions noinline instead of replying on the attributres for this.
GCC seems to complain about inlining coroutines: https://godbolt.org/z/KrzE1znno, not fully sure why.

Well, *properly* inlining a coroutine requires merging the functions in ways that LLVM's representation wouldn't really support, and I assume that's true of GCC's representation as well. The best we can do is lower the coroutine and then inline the ramp function, which is not really the same thing. So warning about marking a coroutine always_inline does make some sense.

As for the CoroEarly pass, it lowers a bunch of intrinsics. Technically I think they can all be done in the front-end. But moving some complexity out of front-end to IR seems reasonable to me.

Ah, if the pass does more than just setting the attribute, then sure, it makes sense to keep it. But I do think we should be requiring the attribute to be added by frontends, since it's really an IR invariant that it's present on all unlowered coroutines.

[ChuanqiXu]

This patch looks OK to me.

The best we can do is lower the coroutine and then inline the ramp function, which is not really the same thing. So warning about marking a coroutine always_inline does make some sense.

It makes sense to emit a warning instead of an error. The example above emits an error which is surprising.

[lxfind]

Ah, if the pass does more than just setting the attribute, then sure, it makes sense to keep it. But I do think we should be requiring the attribute to be added by frontends, since it's really an IR invariant that it's present on all unlowered coroutines.

By the way, it also sets these attributes for other types of coroutines (retcon and async). So the down-side would be then we need to do this for all front-ends (clang and swift).

[ChuanqiXu]

In D100282#2682297, @lxfind wrote:

Ah, if the pass does more than just setting the attribute, then sure, it makes sense to keep it. But I do think we should be requiring the attribute to be added by frontends, since it's really an IR invariant that it's present on all unlowered coroutines.

By the way, it also sets these attributes for other types of coroutines (retcon and async). So the down-side would be then we need to do this for all front-ends (clang and swift).

If it is OK to add these attributes in clang only, and leave other codes handling retcon and async in the Coro-early pass? Since they use special intrinsics, it looks good if we don't edit corresponding part in Coro-early pass.

[rjmccall]

We don't have so many coroutine-emitting frontends that it's unreasonable to modify them all. Swift can make this change; it's not on you to do it. (I also work on the Swift frontend, so don't worry, I'm signing my own teammates up for work here.)

[lxfind]

Set the attributes in Clang instead of CoroEarly

[lxfind]

Update test

[rjmccall]

LGTM

[ychen]

I think the setting is in CoroEarly from the beginning is that it is an implementation detail? Clients should only worry about coroutine shape. Maybe we could set noinline in frontends to express the intent and remove it in coroearly/corosplit?

[rjmccall]

That something is an (unlowered) coroutine is an important semantic property of the function that should be represented more explicitly in IR than just whether it contains a call to an intrinsic in the llvm.coro.id family. Coroutines have somewhat different structural rules from ordinary functions, as is natural for a somewhat different high-level concept. noinline is an independent attribute that should affect whether the ramp function is inlinable after coroutine lowering is complete.

In principle, I would prefer that we use a better attribute than this coro.presplit thing — a few years ago, I proposed adding a directly-supported coroutine attribute which would take the lowering style as an argument. So if someone's willing to do to the work to jump to that instead of going through this intermediate stage, then okay, let's do it.

[lxfind]

In D100282#2687532, @ychen wrote:

I think the setting is in CoroEarly from the beginning is that it is an implementation detail? Clients should only worry about coroutine shape. Maybe we could set noinline in frontends to express the intent and remove it in coroearly/corosplit?

We cannot do that, because we need to distinguish between user-specified noinline vs coroutine. Some coroutines in theory could potentially be inlined.
Our choice is really just between setting it in the front-end or moving CoroEarly to the beginning of the pipeline.

[ChuanqiXu]

I agree with the idea we should set the attribute in the frontend or move Coro-early pass in the front. It looks more weird to add a noinline attribute and move it later.

[lxfind]

This broke MLIR tests.
It seems that MLIR tests depend on CoroEarly to be able to annotate coroutine function properly based on the intrinsics.
Given that, I am now convinced we shouldn't set the attribute in the frontend. Instead we should simply move CoroEarly to before AlwaysInliner.

[rjmccall]

MLIR is an in-tree project that can be updated.

[lxfind]

In D100282#2699171, @rjmccall wrote:

MLIR is an in-tree project that can be updated.

Sure, but I think there are some important differences.
As far as I understand, in MLIR, unlike in C++/Swift frontend where a coroutine function body is represented by an explicit AST type, there is no concept for coroutine functions. Instead functions just contain async dialects. So for MLIR to properly annotate coroutine functions, it will need to look for either those dialects or these intrinsics after IRGen in order to do so, which is pretty much the same thing that we were doing in CoroEarly to annotate coroutine functions. The complexity introduced by duplicating this to all frontends, especially in MLIR where we need to do the same thing as we were doing in CoroEarly, seems to out-weight the benefits on conceptual clarity.

[ChuanqiXu]

This should be covered in: https://reviews.llvm.org/D115790

clang/lib/CodeGen/CGCoroutine.cpp

void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
 
   auto *CoroId = Builder.CreateCall(
       CGM.getIntrinsic(llvm::Intrinsic::coro_id),
       {Builder.getInt32(NewAlign), NullPtr, NullPtr, NullPtr});
   createCoroData(*this, CurCoro, CoroId);
   CurCoro.Data->SuspendBB = RetBB;
   assert(ShouldEmitLifetimeMarkers &&
          "Must emit lifetime intrinsics for coroutines");
+  // CORO_PRESPLIT_ATTR = UNPREPARED_FOR_SPLIT
+  CurFn->addFnAttr("coroutine.presplit", "0");
 
   // Backend is allowed to elide memory allocations, to help it, emit
   // auto mem = coro.alloc() ? 0 : ... allocation code ...;
   auto *CoroAlloc = Builder.CreateCall(
       CGM.getIntrinsic(llvm::Intrinsic::coro_alloc), {CoroId});
 
   Builder.CreateCondBr(CoroAlloc, AllocBB, InitBB);
 

clang/test/CodeGenCoroutines/coro-always-inline-resume.cpp

 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
 // RUN:   -fexperimental-new-pass-manager -O0 %s -o - | FileCheck %s
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
 // RUN:   -fexperimental-new-pass-manager -fno-inline -O0 %s -o - | FileCheck %s
 
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
 // RUN:   -O0 %s -o - | FileCheck %s
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
 // RUN:   -fno-inline -O0 %s -o - | FileCheck %s
 
 namespace std {
 namespace experimental {
 
 struct handle {};
 
 struct awaitable {
   bool await_ready() noexcept { return true; }
   // CHECK-NOT: await_suspend
   inline void __attribute__((__always_inline__)) await_suspend(handle) noexcept {}
   bool await_resume() noexcept { return true; }
 };
 
 template <typename T>
 struct coroutine_handle {
   static handle from_address(void *address) noexcept { return {}; }
 };
 
 template <typename T = void>
 struct coroutine_traits {
   struct promise_type {
     awaitable initial_suspend() { return {}; }
     awaitable final_suspend() noexcept { return {}; }
     void return_void() {}
     T get_return_object() { return T(); }
     void unhandled_exception() {}
   };
 };
 } // namespace experimental
 } // namespace std
 
 // CHECK-LABEL: @_Z3foov
 // CHECK-LABEL: entry:
 // CHECK-NEXT: %this.addr.i{{[0-9]*}} = alloca %"struct.std::experimental::awaitable"*, align 8
 // CHECK-NEXT: %this.addr.i{{[0-9]*}} = alloca %"struct.std::experimental::awaitable"*, align 8
 // CHECK: [[CAST0:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 8, i8* [[CAST0]])
 // CHECK: [[CAST1:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 8, i8* [[CAST1]])
 
 // CHECK: [[CAST2:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 8, i8* [[CAST2]])
 // CHECK: [[CAST3:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
 // CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 8, i8* [[CAST3]])
 void foo() { co_return; }

clang/test/CodeGenCoroutines/coro-always-inline.cpp

-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
-// RUN:   -fexperimental-new-pass-manager -O0 %s -o - | FileCheck %s
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
-// RUN:   -fexperimental-new-pass-manager -fno-inline -O0 %s -o - | FileCheck %s
-
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
-// RUN:   -O0 %s -o - | FileCheck %s
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fcoroutines-ts \
-// RUN:   -fno-inline -O0 %s -o - | FileCheck %s
-
-namespace std {
-namespace experimental {
-
-struct handle {};
-
-struct awaitable {
-  bool await_ready() noexcept { return true; }
-  // CHECK-NOT: await_suspend
-  inline void __attribute__((__always_inline__)) await_suspend(handle) noexcept {}
-  bool await_resume() noexcept { return true; }
+// RUN: %clang -std=c++2a %s -emit-llvm -S -o - | FileCheck %s
+
+#include "Inputs/coroutine.h"
+
+namespace coro = std::experimental::coroutines_v1;
+
+class task {
+public:
+  class promise_type {
+  public:
+    task get_return_object() noexcept;
+    coro::suspend_always initial_suspend() noexcept;
+    void return_void() noexcept;
+    void unhandled_exception() noexcept;
+
+    struct final_awaiter {
+      bool await_ready() noexcept;
+      void await_suspend(coro::coroutine_handle<promise_type> h) noexcept;
+      void await_resume() noexcept;
     };
 
-template <typename T>
-struct coroutine_handle {
-  static handle from_address(void *address) noexcept { return {}; }
+    final_awaiter final_suspend() noexcept;
+
+    coro::coroutine_handle<> continuation;
   };
 
-template <typename T = void>
-struct coroutine_traits {
-  struct promise_type {
-    awaitable initial_suspend() { return {}; }
-    awaitable final_suspend() noexcept { return {}; }
-    void return_void() {}
-    T get_return_object() { return T(); }
-    void unhandled_exception() {}
+  task(task &&t) noexcept;
+  ~task();
+
+  class awaiter {
+  public:
+    bool await_ready() noexcept;
+    void await_suspend(coro::coroutine_handle<> continuation) noexcept;
+    void await_resume() noexcept;
+
+  private:
+    friend task;
+    explicit awaiter(coro::coroutine_handle<promise_type> h) noexcept;
+    coro::coroutine_handle<promise_type> coro_;
   };
+
+  awaiter operator co_await() &&noexcept;
+
+private:
+  explicit task(coro::coroutine_handle<promise_type> h) noexcept;
+  coro::coroutine_handle<promise_type> coro_;
 };
-} // namespace experimental
-} // namespace std
 
-// CHECK-LABEL: @_Z3foov
-// CHECK-LABEL: entry:
-// CHECK-NEXT: %this.addr.i{{[0-9]*}} = alloca %"struct.std::experimental::awaitable"*, align 8
-// CHECK-NEXT: %this.addr.i{{[0-9]*}} = alloca %"struct.std::experimental::awaitable"*, align 8
-// CHECK: [[CAST0:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
-// CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 8, i8* [[CAST0]])
-// CHECK: [[CAST1:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
-// CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 8, i8* [[CAST1]])
-
-// CHECK: [[CAST2:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
-// CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 8, i8* [[CAST2]])
-// CHECK: [[CAST3:%[0-9]+]] = bitcast %"struct.std::experimental::awaitable"** %this.addr.i{{[0-9]*}} to i8*
-// CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 8, i8* [[CAST3]])
-void foo() { co_return; }
+task cee();
+
+__attribute__((always_inline)) inline task bar() {
+  co_await cee();
+  co_return;
+}
+
+task foo() {
+  co_await bar();
+  co_return;
+}
+
+// check that bar is not inlined even it's marked as always_inline
+
+// CHECK-LABEL: define void @_Z3foov(
+// CHECK:         invoke void @_Z3barv(

llvm/lib/Transforms/Coroutines/CoroEarly.cpp

if (auto *CB = dyn_cast<CallBase>(&I)) {
       case Intrinsic::coro_noop:
         lowerCoroNoop(cast<IntrinsicInst>(&I));
         break;
       case Intrinsic::coro_id:
         // Mark a function that comes out of the frontend that has a coro.id
         // with a coroutine attribute.
         if (auto *CII = cast<CoroIdInst>(&I)) {
           if (CII->getInfo().isPreSplit()) {
-            F.addFnAttr(CORO_PRESPLIT_ATTR, UNPREPARED_FOR_SPLIT);
             setCannotDuplicate(CII);
             CII->setCoroutineSelf();
             CoroId = cast<CoroIdInst>(&I);
           }
         }
         break;
       case Intrinsic::coro_id_retcon:
       case Intrinsic::coro_id_retcon_once:

llvm/test/Transforms/Coroutines/coro-debug-O2.ll

 ; RUN: opt < %s -coro-early -coro-split -reuse-storage-in-coroutine-frame -coro-split -sroa -S | FileCheck %s
 
 ; Checks whether the dbg.declare for `__promise` remains valid under O2.
 
 ; CHECK-LABEL: define internal fastcc void @f.resume({{.*}})
 ; CHECK:       entry.resume:
 ; CHECK:        call void @llvm.dbg.declare(metadata %f.Frame* %FramePtr, metadata ![[PROMISEVAR_RESUME:[0-9]+]], metadata !DIExpression(
 ;
 ; CHECK: ![[PROMISEVAR_RESUME]] = !DILocalVariable(name: "__promise"
 %promise_type = type { i32, i32, double }
 
-define void @f() !dbg !8 {
+define void @f() "coroutine.presplit"="0" !dbg !8 {
 entry:
     %__promise = alloca %promise_type, align 8
     %0 = bitcast %promise_type* %__promise to i8*
     %id = call token @llvm.coro.id(i32 16, i8* %0, i8* null, i8* null)
     %alloc = call i1 @llvm.coro.alloc(token %id)
     br i1 %alloc, label %coro.alloc, label %coro.init
 
 coro.alloc:                                       ; preds = %entry

llvm/test/Transforms/Coroutines/coro-debug-frame-variable.ll

 ; CHECK: ![[JDBGLOC]] = !DILocation(line: 32, column: 7, scope: ![[SCOPE]])
 
 ; CHECK: ![[XVAR_RESUME]] = !DILocalVariable(name: "x"
 ; CHECK: ![[IDBGLOC_RESUME]] = !DILocation(line: 24, column: 7, scope: ![[RESUME_SCOPE:[0-9]+]])
 ; CHECK: ![[RESUME_SCOPE]] = distinct !DILexicalBlock(scope: !8, file: !1, line: 23, column: 12)
 ; CHECK: ![[IVAR_RESUME]] = !DILocalVariable(name: "i"
 ; CHECK: ![[JVAR_RESUME]] = !DILocalVariable(name: "j"
 ; CHECK: ![[JDBGLOC_RESUME]] = !DILocation(line: 32, column: 7, scope: ![[RESUME_SCOPE]])
-define void @f() {
+define void @f() "coroutine.presplit"="0" {
 entry:
   %__promise = alloca i8, align 8
   %i = alloca i32, align 4
   %j = alloca i32, align 4
   %x = alloca [10 x i32], align 16
   %id = call token @llvm.coro.id(i32 16, i8* %__promise, i8* null, i8* null)
   %alloc = call i1 @llvm.coro.alloc(token %id)
   br i1 %alloc, label %coro.alloc, label %coro.init

llvm/test/Transforms/Coroutines/coro-split-01.ll

 ; Tests that a coroutine is split, inlined into the caller and devirtualized.
 ; RUN: opt < %s -S -enable-coroutines -O2 | FileCheck %s
 ; RUN: opt < %s -S -enable-coroutines -passes='default<O2>' | FileCheck %s
 
-define i8* @f() {
+define i8* @f() "coroutine.presplit"="0" {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
   br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
 dyn.alloc:
   %size = call i32 @llvm.coro.size.i32()
   %alloc = call i8* @malloc(i32 %size)
   br label %coro.begin

llvm/test/Transforms/Coroutines/coro-split-recursive.ll

 ; RUN: opt -passes='default<O2>' -enable-coroutines -S < %s | FileCheck %s
 
 declare token @llvm.coro.id(i32, i8* readnone, i8* nocapture readonly, i8*)
 
 declare i8* @llvm.coro.begin(token, i8* writeonly)
 
 declare token @llvm.coro.save(i8*)
 
 declare i8 @llvm.coro.suspend(token, i1)
 
 ; CHECK-LABEL: define void @foo()
 ; CHECK-LABEL: define {{.*}}void @foo.resume(
 ; CHECK: call void @foo()
 ; CHECK-LABEL: define {{.*}}void @foo.destroy(
 
-define void @foo() {
+define void @foo() "coroutine.presplit"="0" {
 entry:
   %__promise = alloca i32, align 8
   %0 = bitcast i32* %__promise to i8*
   %1 = call token @llvm.coro.id(i32 16, i8* %0, i8* null, i8* null)
   %2 = call i8* @llvm.coro.begin(token %1, i8* null)
   br i1 undef, label %if.then154, label %init.suspend
 
 init.suspend:                                     ; preds = %entry

llvm/test/Transforms/Coroutines/ex0.ll

 ; First example from Doc/Coroutines.rst (two block loop)
 ; RUN: opt < %s -enable-coroutines -O2 -preserve-alignment-assumptions-during-inlining=false -S | FileCheck %s
 ; RUN: opt < %s -enable-coroutines -aa-pipeline=basic-aa -passes='default<O2>' -preserve-alignment-assumptions-during-inlining=false -S | FileCheck %s
 
-define i8* @f(i32 %n) {
+define i8* @f(i32 %n) "coroutine.presplit"="0" {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %size = call i32 @llvm.coro.size.i32()
   %alloc = call i8* @malloc(i32 %size)
   %hdl = call i8* @llvm.coro.begin(token %id, i8* %alloc)
   br label %loop
 
 loop:

llvm/test/Transforms/Coroutines/ex1.ll

 ; First example from Doc/Coroutines.rst (one block loop)
 ; RUN: opt < %s -O2 -enable-coroutines -preserve-alignment-assumptions-during-inlining=false -S | FileCheck %s
 ; RUN: opt < %s -aa-pipeline=basic-aa -passes='default<O2>' -enable-coroutines -preserve-alignment-assumptions-during-inlining=false -S | FileCheck %s
 
-define i8* @f(i32 %n) {
+define i8* @f(i32 %n) "coroutine.presplit"="0" {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %size = call i32 @llvm.coro.size.i32()
   %alloc = call i8* @malloc(i32 %size)
   %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
   br label %loop
 loop:
   %n.val = phi i32 [ %n, %entry ], [ %inc, %loop ]

llvm/test/Transforms/Coroutines/ex2.ll

 ; Second example from Doc/Coroutines.rst (custom alloc and free functions)
 ; RUN: opt < %s -O2 -enable-coroutines -S | FileCheck %s
 ; RUN: opt < %s -passes='default<O2>' -enable-coroutines -S | FileCheck %s
 
-define i8* @f(i32 %n) {
+define i8* @f(i32 %n) "coroutine.presplit"="0" {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
   br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
 dyn.alloc:
   %size = call i32 @llvm.coro.size.i32()
   %alloc = call i8* @CustomAlloc(i32 %size)
   br label %coro.begin

llvm/test/Transforms/Coroutines/ex3.ll

 ; Third example from Doc/Coroutines.rst (two suspend points)
 ; RUN: opt < %s -O2 -enable-coroutines -S | FileCheck %s
 ; RUN: opt < %s -aa-pipeline=basic-aa -passes='default<O2>' -enable-coroutines -S | FileCheck %s
 
-define i8* @f(i32 %n) {
+define i8* @f(i32 %n) "coroutine.presplit"="0" {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %size = call i32 @llvm.coro.size.i32()
   %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
   br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
 dyn.alloc:
   %alloc = call i8* @malloc(i32 %size)
   br label %coro.begin

llvm/test/Transforms/Coroutines/ex4.ll

 ; Fourth example from Doc/Coroutines.rst (coroutine promise)
 ; RUN: opt < %s -O2 -enable-coroutines -S | FileCheck %s
 ; RUN: opt < %s -passes='default<O2>' -enable-coroutines -S | FileCheck %s
 
-define i8* @f(i32 %n) {
+define i8* @f(i32 %n) "coroutine.presplit"="0" {
 entry:
   %promise = alloca i32
   %pv = bitcast i32* %promise to i8*
   %id = call token @llvm.coro.id(i32 0, i8* %pv, i8* null, i8* null)
   %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
   br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
 dyn.alloc:
   %size = call i32 @llvm.coro.size.i32()

llvm/test/Transforms/Coroutines/ex5.ll

 ; Fifth example from Doc/Coroutines.rst (final suspend)
 ; RUN: opt < %s -O2 -enable-coroutines -preserve-alignment-assumptions-during-inlining=false -S | FileCheck %s
 ; RUN: opt < %s -aa-pipeline=basic-aa -passes='default<O2>' -enable-coroutines -preserve-alignment-assumptions-during-inlining=false -S | FileCheck %s
 
-define i8* @f(i32 %n) {
+define i8* @f(i32 %n) "coroutine.presplit"="0" {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %size = call i32 @llvm.coro.size.i32()
   %alloc = call i8* @malloc(i32 %size)
   %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
   br label %while.cond
 while.cond:
   %n.val = phi i32 [ %n, %entry ], [ %dec, %while.body ]

llvm/test/Transforms/Coroutines/phi-coro-end.ll

 ; Verify that we correctly handle suspend when the coro.end block contains phi
 ; RUN: opt < %s -O2 -enable-coroutines -S | FileCheck %s
 ; RUN: opt < %s -aa-pipeline=basic-aa -passes='default<O2>' -enable-coroutines -S | FileCheck %s
 
-define i8* @f(i32 %n) {
+define i8* @f(i32 %n) "coroutine.presplit"="0" {
 entry:
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %size = call i32 @llvm.coro.size.i32()
   %alloc = call i8* @malloc(i32 %size)
   %hdl = call i8* @llvm.coro.begin(token %id, i8* %alloc)
   %0 = call i8 @llvm.coro.suspend(token none, i1 false)
   switch i8 %0, label %suspend [i8 0, label %cleanup i8 1, label %cleanup]
 

llvm/test/Transforms/Coroutines/restart-trigger.ll

 ; Verifies that the restart trigger that is used by legacy coroutine passes
 ; forces the legacy pass manager to restart IPO pipelines, thereby causing the
 ; same coroutine to be looked at by CoroSplit pass twice.
 ; REQUIRES: asserts
 ; RUN: opt < %s -S -O0 -enable-coroutines -debug-only=coro-split 2>&1 | FileCheck %s
 ; RUN: opt < %s -S -O1 -enable-coroutines -debug-only=coro-split 2>&1 | FileCheck %s
 ; The following tests use the new pass manager, and verify that the coroutine
 ; passes re-run the CGSCC pipeline.
 ; RUN: opt < %s -S -passes='default<O0>' -enable-coroutines -debug-only=coro-split 2>&1 | FileCheck %s
 ; RUN: opt < %s -S -passes='default<O1>' -enable-coroutines -debug-only=coro-split 2>&1 | FileCheck %s
 
 ; CHECK:      CoroSplit: Processing coroutine 'f' state: 0
 ; CHECK-NEXT: CoroSplit: Processing coroutine 'f' state: 1
 
-define void @f() {
+define void @f() "coroutine.presplit"="0" {
   %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
   %size = call i32 @llvm.coro.size.i32()
   %alloc = call i8* @malloc(i32 %size)
   %hdl = call i8* @llvm.coro.begin(token %id, i8* %alloc)
   call void @print(i32 0)
   %s1 = call i8 @llvm.coro.suspend(token none, i1 false)
   switch i8 %s1, label %suspend [i8 0, label %resume 
                                  i8 1, label %cleanup]