From 422c1ecfb96ec0df41af0e3333383a5e01722990 Mon Sep 17 00:00:00 2001
From: Varun Gandhi <varun_gandhi@apple.com>
Date: Tue, 30 Mar 2021 15:03:16 -0700
Subject: [PATCH 1/3] Use musttail in MergeFunctions for swiftasync->swiftasync
 tail calls.

Fixes rdar://76024125.
---
 llvm/lib/Transforms/IPO/MergeFunctions.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 91af6e0cb72e1..d7892869525bc 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -709,7 +709,11 @@ void MergeFunctions::writeThunk(Function *F, Function *G) {
 
   CallInst *CI = Builder.CreateCall(F, Args);
   ReturnInst *RI = nullptr;
-  CI->setTailCall();
+  bool isSwiftTailCall =
+   F->getCallingConv() == CallingConv::SwiftTail &&
+   G->getCallingConv() == CallingConv::SwiftTail;
+  CI->setTailCallKind(
+    isSwiftTailCall ? llvm::CallInst::TCK_MustTail : llvm::CallInst::TCK_Tail);
   CI->setCallingConv(F->getCallingConv());
   CI->setAttributes(F->getAttributes());
   if (H->getReturnType()->isVoidTy()) {

From bdad91989b36e821021d137fafe5329765921c77 Mon Sep 17 00:00:00 2001
From: Varun Gandhi <varun_gandhi@apple.com>
Date: Tue, 30 Mar 2021 15:15:47 -0700
Subject: [PATCH 2/3] Update musttail verification to check all
 swiftasync->swiftasync tail calls.

When -enable-swifttailcc-musttail-check is passed (off by default), we will
check that all swiftasync->swiftasync tail calls are marked musttail.

Fixes rdar://75899279.
---
 llvm/lib/IR/Verifier.cpp | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index c0ff810458aa4..523e006bb34ac 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -3430,7 +3430,24 @@ static AttrBuilder getParameterABIAttributes(int I, AttributeList Attrs) {
   return Copy;
 }
 
+static cl::opt<bool>
+EnableSwiftTailCCMustTailCheck("enable-swifttailcc-musttail-check",
+cl::init(false), cl::desc("Check that tail calls from swifttailcc functions to"
+                          " swifttailcc functions are marked musttail."));
+
 void Verifier::verifyMustTailCall(CallInst &CI) {
+  if (!CI.isMustTailCall()) {
+    if (EnableSwiftTailCCMustTailCheck &&
+        CI.getCallingConv() == CallingConv::SwiftTail &&
+        CI.getCaller()->getCallingConv() == CallingConv::SwiftTail &&
+        isa_and_nonnull<ReturnInst>(CI.getNextNode())) {
+      Assert(
+        false, "tail call from swifttail->swiftail should be marked musttail",
+        &CI);
+    }
+    return;
+  }
+
   Assert(!CI.isInlineAsm(), "cannot use musttail call with inline asm", &CI);
 
   Function *F = CI.getParent()->getParent();
@@ -3515,9 +3532,7 @@ void Verifier::verifyMustTailCall(CallInst &CI) {
 
 void Verifier::visitCallInst(CallInst &CI) {
   visitCallBase(CI);
-
-  if (CI.isMustTailCall())
-    verifyMustTailCall(CI);
+  verifyMustTailCall(CI);
 }
 
 void Verifier::visitInvokeInst(InvokeInst &II) {

From 7220c40793d731ed06be0a05c7ec0838c33d475a Mon Sep 17 00:00:00 2001
From: Varun Gandhi <varun_gandhi@apple.com>
Date: Wed, 26 May 2021 11:28:24 -0700
Subject: [PATCH 3/3] Use additional musttail checking only in debug builds.

---
 llvm/lib/IR/Verifier.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 523e006bb34ac..3da7138d730a2 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -3437,6 +3437,7 @@ cl::init(false), cl::desc("Check that tail calls from swifttailcc functions to"
 
 void Verifier::verifyMustTailCall(CallInst &CI) {
   if (!CI.isMustTailCall()) {
+#ifndef NDEBUG
     if (EnableSwiftTailCCMustTailCheck &&
         CI.getCallingConv() == CallingConv::SwiftTail &&
         CI.getCaller()->getCallingConv() == CallingConv::SwiftTail &&
@@ -3445,6 +3446,7 @@ void Verifier::verifyMustTailCall(CallInst &CI) {
         false, "tail call from swifttail->swiftail should be marked musttail",
         &CI);
     }
+#endif
     return;
   }