Index: clang/lib/CodeGen/CGCoroutine.cpp
===================================================================
--- clang/lib/CodeGen/CGCoroutine.cpp
+++ clang/lib/CodeGen/CGCoroutine.cpp
@@ -703,6 +703,9 @@
 
   if (Stmt *Ret = S.getReturnStmt())
     EmitStmt(Ret);
+
+  assert(CurFn);
+  CurFn->addFnAttr("coroutine.presplit", "0");
 }
 
 // Emit coroutine intrinsic and patch up arguments of the token type.
Index: clang/test/CodeGenCoroutines/coro-attributes.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCoroutines/coro-attributes.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 -disable-llvm-passes -emit-llvm %s -o - | FileCheck %s
+#include "Inputs/coroutine.h"
+
+using namespace std;
+
+struct coro {
+  struct promise_type {
+    coro get_return_object();
+    suspend_never initial_suspend();
+    suspend_never final_suspend() noexcept;
+    void return_void();
+    static void unhandled_exception();
+  };
+};
+
+// CHECK: void @_Z3foov() #[[FOO_ATTR_NUM:[0-9]+]]
+// CHECK: attributes #[[FOO_ATTR_NUM]] = { {{.*}} "coroutine.presplit"="0"
+coro foo() {
+  co_await suspend_always{};
+}
Index: llvm/docs/Coroutines.rst
===================================================================
--- llvm/docs/Coroutines.rst
+++ llvm/docs/Coroutines.rst
@@ -1175,6 +1175,9 @@
 
 A frontend should emit exactly one `coro.id` intrinsic per coroutine.
 
+The frontend should add attribute `"coroutine.presplit"` with value `"0"` for the coroutine
+containing `coro.id`.
+
 .. _coro.id.async:
 
 'llvm.coro.id.async' Intrinsic
Index: llvm/lib/Transforms/Coroutines/CoroEarly.cpp
===================================================================
--- llvm/lib/Transforms/Coroutines/CoroEarly.cpp
+++ llvm/lib/Transforms/Coroutines/CoroEarly.cpp
@@ -180,7 +180,6 @@
         // 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);
Index: llvm/lib/Transforms/Coroutines/CoroInternal.h
===================================================================
--- llvm/lib/Transforms/Coroutines/CoroInternal.h
+++ llvm/lib/Transforms/Coroutines/CoroInternal.h
@@ -36,6 +36,10 @@
 // adds coroutine subfunctions to the SCC to be processed by IPO pipeline.
 // Async lowering similarily triggers a restart of the pipeline after it has
 // split the coroutine.
+//
+// FIXME: Refactor these attributes as LLVM attributes instead of string
+// attributes since these attributes are already used outside the LLVM's
+// coroutine module.
 #define CORO_PRESPLIT_ATTR "coroutine.presplit"
 #define UNPREPARED_FOR_SPLIT "0"
 #define PREPARED_FOR_SPLIT "1"
Index: llvm/test/Transforms/Coroutines/coro-debug-O2.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-debug-O2.ll
+++ llvm/test/Transforms/Coroutines/coro-debug-O2.ll
@@ -9,7 +9,7 @@
 ; 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*
Index: llvm/test/Transforms/Coroutines/coro-debug-coro-frame.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-debug-coro-frame.ll
+++ llvm/test/Transforms/Coroutines/coro-debug-coro-frame.ll
@@ -56,7 +56,7 @@
 declare void @pi64(i64*)
 declare void @pdouble(double*)
 
-define void @f(i32 %a, i32 %b, i64 %c, double %d) !dbg !8 {
+define void @f(i32 %a, i32 %b, i64 %c, double %d) "coroutine.presplit"="0" !dbg !8 {
 entry:
     %__promise = alloca %promise_type, align 8
     %0 = bitcast %promise_type* %__promise to i8*
@@ -182,7 +182,7 @@
 
 }
 
-define void @bar(i32 %a, i64 %c, double %d) !dbg !19 {
+define void @bar(i32 %a, i64 %c, double %d) "coroutine.presplit"="0" !dbg !19 {
 entry:
     %__promise = alloca %promise_type, align 8
     %0 = bitcast %promise_type* %__promise to i8*
Index: llvm/test/Transforms/Coroutines/coro-debug-dbg.values-not_used_in_frame.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-debug-dbg.values-not_used_in_frame.ll
+++ llvm/test/Transforms/Coroutines/coro-debug-dbg.values-not_used_in_frame.ll
@@ -13,7 +13,7 @@
 
 source_filename = "../llvm/test/Transforms/Coroutines/coro-debug-dbg.values-O2.ll"
 
-define void @f(i32 %i, i32 %j) !dbg !8 {
+define void @f(i32 %i, i32 %j) "coroutine.presplit"="0" !dbg !8 {
 entry:
   %__promise = alloca i8, align 8
   %x = alloca [10 x i32], align 16
Index: llvm/test/Transforms/Coroutines/coro-debug-dbg.values.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-debug-dbg.values.ll
+++ llvm/test/Transforms/Coroutines/coro-debug-dbg.values.ll
@@ -19,7 +19,7 @@
 source_filename = "../llvm/test/Transforms/Coroutines/coro-debug-dbg.values-O2.ll"
 declare void @consume(i32)
 
-define void @f(i32 %i, i32 %j) !dbg !8 {
+define void @f(i32 %i, i32 %j) "coroutine.presplit"="0" !dbg !8 {
 entry:
   %__promise = alloca i8, align 8
   %x = alloca [10 x i32], align 16
Index: llvm/test/Transforms/Coroutines/coro-debug-frame-variable.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-debug-frame-variable.ll
+++ llvm/test/Transforms/Coroutines/coro-debug-frame-variable.ll
@@ -62,7 +62,7 @@
 ; 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
Index: llvm/test/Transforms/Coroutines/coro-split-01.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-split-01.ll
+++ llvm/test/Transforms/Coroutines/coro-split-01.ll
@@ -1,7 +1,7 @@
 ; Tests that a coroutine is split, inlined into the caller and devirtualized.
 ; 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)
Index: llvm/test/Transforms/Coroutines/coro-split-recursive.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-split-recursive.ll
+++ llvm/test/Transforms/Coroutines/coro-split-recursive.ll
@@ -13,7 +13,7 @@
 ; 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*
Index: llvm/test/Transforms/Coroutines/ex0.ll
===================================================================
--- llvm/test/Transforms/Coroutines/ex0.ll
+++ llvm/test/Transforms/Coroutines/ex0.ll
@@ -1,7 +1,7 @@
 ; First example from Doc/Coroutines.rst (two block loop)
 ; 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()
Index: llvm/test/Transforms/Coroutines/ex1.ll
===================================================================
--- llvm/test/Transforms/Coroutines/ex1.ll
+++ llvm/test/Transforms/Coroutines/ex1.ll
@@ -1,7 +1,7 @@
 ; First example from Doc/Coroutines.rst (one block loop)
 ; 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()
Index: llvm/test/Transforms/Coroutines/ex2.ll
===================================================================
--- llvm/test/Transforms/Coroutines/ex2.ll
+++ llvm/test/Transforms/Coroutines/ex2.ll
@@ -1,7 +1,7 @@
 ; Second example from Doc/Coroutines.rst (custom alloc and free functions)
 ; 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)
Index: llvm/test/Transforms/Coroutines/ex3.ll
===================================================================
--- llvm/test/Transforms/Coroutines/ex3.ll
+++ llvm/test/Transforms/Coroutines/ex3.ll
@@ -1,7 +1,7 @@
 ; Third example from Doc/Coroutines.rst (two suspend points)
 ; 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()
Index: llvm/test/Transforms/Coroutines/ex4.ll
===================================================================
--- llvm/test/Transforms/Coroutines/ex4.ll
+++ llvm/test/Transforms/Coroutines/ex4.ll
@@ -1,7 +1,7 @@
 ; Fourth example from Doc/Coroutines.rst (coroutine promise)
 ; 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*
Index: llvm/test/Transforms/Coroutines/ex5.ll
===================================================================
--- llvm/test/Transforms/Coroutines/ex5.ll
+++ llvm/test/Transforms/Coroutines/ex5.ll
@@ -1,7 +1,7 @@
 ; Fifth example from Doc/Coroutines.rst (final suspend)
 ; 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()
Index: llvm/test/Transforms/Coroutines/phi-coro-end.ll
===================================================================
--- llvm/test/Transforms/Coroutines/phi-coro-end.ll
+++ llvm/test/Transforms/Coroutines/phi-coro-end.ll
@@ -1,7 +1,7 @@
 ; Verify that we correctly handle suspend when the coro.end block contains phi
 ; 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()
Index: llvm/test/Transforms/Coroutines/restart-trigger.ll
===================================================================
--- llvm/test/Transforms/Coroutines/restart-trigger.ll
+++ llvm/test/Transforms/Coroutines/restart-trigger.ll
@@ -10,7 +10,7 @@
 ; CHECK-NEWPM-NOT:  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)