[clang] [coroutine] Suppress unreachable-code warning on coroutine statements. (PR #77454)

[Utkarsh Saxena via cfe-commits]

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@@ -453,26 +454,68 @@ bool DeadCodeScan::isDeadCodeRoot(const clang::CFGBlock *Block) {
   return isDeadRoot;
 }
 
-static bool isValidDeadStmt(const Stmt *S) {
+// Check if the given `DeadStmt` is a coroutine statement and is a substmt of
+// the coroutine statement.
+static bool isInCoroutineStmt(const Stmt* DeadStmt, const CFGBlock *Block) {
+  // The coroutine statement, co_return, co_await, or co_yield.
+  const Stmt* CoroStmt = nullptr;
+  // Find the first coroutine statement after the DeadStmt in the block.
+  bool AfterDeadStmt = false;
+  for (CFGBlock::const_iterator I = Block->begin(), E = Block->end(); I != E;
+       ++I)
+    if (std::optional<CFGStmt> CS = I->getAs<CFGStmt>()) {
+      const Stmt *S = CS->getStmt();
+      if (S == DeadStmt)
+        AfterDeadStmt = true;
+      if (AfterDeadStmt &&
+          (llvm::isa<CoreturnStmt>(S) || llvm::isa<CoroutineSuspendExpr>(S))) {
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usx95 wrote:

But... that could be fine as well. This could be something where we want the warning. Only simple coroutine stmt could be exempted from this check. (Feel free to ignore the above comment in that case.)

https://github.com/llvm/llvm-project/pull/77454