diff --git a/llvm/include/llvm/IR/Intrinsics.td b/llvm/include/llvm/IR/Intrinsics.td
--- a/llvm/include/llvm/IR/Intrinsics.td
+++ b/llvm/include/llvm/IR/Intrinsics.td
@@ -1216,6 +1216,7 @@
 def int_coro_async_resume : Intrinsic<[llvm_ptr_ty],
     [],
     []>;
+def int_coro_async_size_replace : Intrinsic<[], [llvm_ptr_ty, llvm_ptr_ty], []>;
 def int_coro_suspend_async
     : Intrinsic<[llvm_any_ty], [llvm_ptr_ty, llvm_ptr_ty, llvm_vararg_ty], []>;
 def int_coro_prepare_async : Intrinsic<[llvm_ptr_ty], [llvm_ptr_ty],
diff --git a/llvm/lib/Transforms/Coroutines/CoroCleanup.cpp b/llvm/lib/Transforms/Coroutines/CoroCleanup.cpp
--- a/llvm/lib/Transforms/Coroutines/CoroCleanup.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroCleanup.cpp
@@ -80,6 +80,23 @@
       case Intrinsic::coro_subfn_addr:
         lowerSubFn(Builder, cast<CoroSubFnInst>(II));
         break;
+      case Intrinsic::coro_async_size_replace:
+        auto *Target = cast<ConstantStruct>(
+            cast<GlobalVariable>(II->getArgOperand(0)->stripPointerCasts())
+                ->getInitializer());
+        auto *Source = cast<ConstantStruct>(
+            cast<GlobalVariable>(II->getArgOperand(1)->stripPointerCasts())
+                ->getInitializer());
+        auto *TargetSize = Target->getOperand(1);
+        auto *SourceSize = Source->getOperand(1);
+        if (TargetSize->isElementWiseEqual(SourceSize)) {
+          break;
+        }
+        auto *TargetRelativeFunOffset = Target->getOperand(0);
+        auto *NewFuncPtrStruct = ConstantStruct::get(
+            Target->getType(), TargetRelativeFunOffset, SourceSize);
+        Target->replaceAllUsesWith(NewFuncPtrStruct);
+        break;
       }
       II->eraseFromParent();
       Changed = true;
@@ -95,10 +112,10 @@
 }
 
 static bool declaresCoroCleanupIntrinsics(const Module &M) {
-  return coro::declaresIntrinsics(M, {"llvm.coro.alloc", "llvm.coro.begin",
-                                      "llvm.coro.subfn.addr", "llvm.coro.free",
-                                      "llvm.coro.id", "llvm.coro.id.retcon",
-                                      "llvm.coro.id.retcon.once"});
+  return coro::declaresIntrinsics(
+      M, {"llvm.coro.alloc", "llvm.coro.begin", "llvm.coro.subfn.addr",
+          "llvm.coro.free", "llvm.coro.id", "llvm.coro.id.retcon",
+          "llvm.coro.id.retcon.once", "llvm.coro.async.size.replace"});
 }
 
 PreservedAnalyses CoroCleanupPass::run(Function &F,
diff --git a/llvm/lib/Transforms/Coroutines/CoroInstr.h b/llvm/lib/Transforms/Coroutines/CoroInstr.h
--- a/llvm/lib/Transforms/Coroutines/CoroInstr.h
+++ b/llvm/lib/Transforms/Coroutines/CoroInstr.h
@@ -376,6 +376,18 @@
   }
 };
 
+/// This represents the llvm.coro.async.size.replace instruction.
+class LLVM_LIBRARY_VISIBILITY CoroAsyncSizeReplace : public IntrinsicInst {
+public:
+  // Methods to support type inquiry through isa, cast, and dyn_cast:
+  static bool classof(const IntrinsicInst *I) {
+    return I->getIntrinsicID() == Intrinsic::coro_async_size_replace;
+  }
+  static bool classof(const Value *V) {
+    return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
+  }
+};
+
 /// This represents the llvm.coro.frame instruction.
 class LLVM_LIBRARY_VISIBILITY CoroFrameInst : public IntrinsicInst {
 public:
diff --git a/llvm/lib/Transforms/Coroutines/Coroutines.cpp b/llvm/lib/Transforms/Coroutines/Coroutines.cpp
--- a/llvm/lib/Transforms/Coroutines/Coroutines.cpp
+++ b/llvm/lib/Transforms/Coroutines/Coroutines.cpp
@@ -126,6 +126,7 @@
       "llvm.coro.alloc",
       "llvm.coro.async.context.alloc",
       "llvm.coro.async.context.dealloc",
+      "llvm.coro.async.size.replace",
       "llvm.coro.async.store_resume",
       "llvm.coro.begin",
       "llvm.coro.destroy",
diff --git a/llvm/test/Transforms/Coroutines/coro-async.ll b/llvm/test/Transforms/Coroutines/coro-async.ll
--- a/llvm/test/Transforms/Coroutines/coro-async.ll
+++ b/llvm/test/Transforms/Coroutines/coro-async.ll
@@ -27,6 +27,15 @@
      to i32),
      i32 128    ; Initial async context size without space for frame
 }>
+@my_async_function_pa_fp = constant <{ i32, i32 }>
+  <{ i32 trunc (
+       i64 sub (
+         i64 ptrtoint (void (i8*, %async.task*, %async.actor*)* @my_async_function_pa to i64),
+         i64 ptrtoint (i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @my_async_function_pa_fp, i32 0, i32 1) to i64)
+       )
+     to i32),
+     i32 8
+}>
 
 ; Function that implements the dispatch to the callee function.
 define swiftcc void @my_async_function.my_other_async_function_fp.apply(i8* %fnPtr, i8* %async.ctxt, %async.task* %task, %async.actor* %actor) {
@@ -99,8 +108,15 @@
   unreachable
 }
 
+define void @my_async_function_pa(i8* %ctxt, %async.task* %task, %async.actor* %actor) {
+  call void @llvm.coro.async.size.replace(i8* bitcast (<{i32, i32}>* @my_async_function_pa_fp to i8*), i8* bitcast (<{i32, i32}>* @my_async_function_fp to i8*))
+  call swiftcc void @my_async_function(i8* %ctxt, %async.task* %task, %async.actor* %actor)
+  ret void
+}
+
 ; Make sure we update the async function pointer
 ; CHECK: @my_async_function_fp = constant <{ i32, i32 }> <{ {{.*}}, i32 176 }
+; CHECK: @my_async_function_pa_fp = constant <{ i32, i32 }> <{ {{.*}}, i32 176 }
 ; CHECK: @my_async_function2_fp = constant <{ i32, i32 }> <{ {{.*}}, i32 176 }
 
 ; CHECK-LABEL: define swiftcc void @my_async_function(i8* %async.ctxt, %async.task* %task, %async.actor* %actor) {
@@ -511,3 +527,4 @@
 declare swiftcc void @asyncReturn(i8*, %async.task*, %async.actor*)
 declare swiftcc void @asyncSuspend(i8*, %async.task*, %async.actor*)
 declare i8* @llvm.coro.async.resume()
+declare void @llvm.coro.async.size.replace(i8*, i8*)