From 1fb6c508965d39008f91182b44623a402b24d945 Mon Sep 17 00:00:00 2001
From: TB Schardl <neboat@mit.edu>
Date: Mon, 13 Jun 2022 11:29:55 +0000
Subject: [PATCH] [CGCilk] Fix code generation of unreachable _Cilk_sync
 statements.  Fixes issue #93.

---
 clang/lib/CodeGen/CGCilk.cpp         | 12 +++++++-----
 clang/test/Cilk/unreachable-sync.cpp | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+), 5 deletions(-)
 create mode 100644 clang/test/Cilk/unreachable-sync.cpp

diff --git a/clang/lib/CodeGen/CGCilk.cpp b/clang/lib/CodeGen/CGCilk.cpp
index fd3df8efcc8f0d..6bc5411cbfbca1 100644
--- a/clang/lib/CodeGen/CGCilk.cpp
+++ b/clang/lib/CodeGen/CGCilk.cpp
@@ -431,11 +431,13 @@ llvm::Instruction *CodeGenFunction::EmitSyncRegionStart() {
 void CodeGenFunction::EmitCilkSyncStmt(const CilkSyncStmt &S) {
   llvm::BasicBlock *ContinueBlock = createBasicBlock("sync.continue");
 
-  // If this code is reachable then emit a stop point (if generating
-  // debug info). We have to do this ourselves because we are on the
-  // "simple" statement path.
-  if (HaveInsertPoint())
-    EmitStopPoint(&S);
+  // Check if we are generating unreachable code.
+  if (!HaveInsertPoint())
+    // We don't need to generate actual code.
+    return;
+
+  // Generate a stoppoint if we are emitting debug info.
+  EmitStopPoint(&S);
 
   EnsureSyncRegion();
 
diff --git a/clang/test/Cilk/unreachable-sync.cpp b/clang/test/Cilk/unreachable-sync.cpp
new file mode 100644
index 00000000000000..7aa96518db65da
--- /dev/null
+++ b/clang/test/Cilk/unreachable-sync.cpp
@@ -0,0 +1,18 @@
+// Check that a sync is not inserted when clang recognizes that it is not reachable.
+//
+// RUN: %clang_cc1 -fopencilk -ftapir=none -triple x86_64-unknown-linux-gnu -std=c++11 -emit-llvm %s -o - | FileCheck %s
+int create() {
+  return 1;
+  _Cilk_sync;
+}
+
+// CHECK: define dso_local {{.*}}i32 @_Z6createv()
+// CHECK: {
+// CHECK: ret i32 1
+// CHECK-NOT: sync
+// CHECK: }
+
+int main([[maybe_unused]] int argc, char *argv[]) {
+  int e = create();
+  return 0;
+}