Reapply "[Analyzer][CFG] Correctly handle rebuilt default arg and default init expression" (#127338)

This PR reapply https://github.com/llvm/llvm-project/pull/117437.
The issue has been fixed by the 2nd commit, we need to ignore parens in
CXXDefaultArgExpr when build CFG, because CXXDefaultArgExpr::getExpr
stripped off the top level FullExpr and ConstantExpr, ParenExpr may
occurres in the top level.

---------

Signed-off-by: yronglin <yronglin777@gmail.com>

1 files changed, 19 insertions, 18 deletions

diff --git a/clang/lib/Analysis/ReachableCode.cpp b/clang/lib/Analysis/ReachableCode.cpp
index dd81c8e..3b1f716 100644
--- a/clang/lib/Analysis/ReachableCode.cpp
+++ b/clang/lib/Analysis/ReachableCode.cpp
@@ -454,11 +454,12 @@ bool DeadCodeScan::isDeadCodeRoot(const clang::CFGBlock *Block) {
   return isDeadRoot;
 }
 
-// Check if the given `DeadStmt` is a coroutine statement and is a substmt of
-// the coroutine statement. `Block` is the CFGBlock containing the `DeadStmt`.
-static bool isInCoroutineStmt(const Stmt *DeadStmt, const CFGBlock *Block) {
+// Check if the given `DeadStmt` is one of target statements or is a sub-stmt of
+// them. `Block` is the CFGBlock containing the `DeadStmt`.
+template <class... Ts>
+static bool isDeadStmtInOneOf(const Stmt *DeadStmt, const CFGBlock *Block) {
   // The coroutine statement, co_return, co_await, or co_yield.
-  const Stmt *CoroStmt = nullptr;
+  const Stmt *TargetStmt = 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;
@@ -467,32 +468,27 @@ static bool isInCoroutineStmt(const Stmt *DeadStmt, const CFGBlock *Block) {
       const Stmt *S = CS->getStmt();
       if (S == DeadStmt)
         AfterDeadStmt = true;
-      if (AfterDeadStmt &&
-          // For simplicity, we only check simple coroutine statements.
-          (llvm::isa<CoreturnStmt>(S) || llvm::isa<CoroutineSuspendExpr>(S))) {
-        CoroStmt = S;
+      if (AfterDeadStmt && llvm::isa<Ts...>(S)) {
+        TargetStmt = S;
         break;
       }
     }
-  if (!CoroStmt)
+  if (!TargetStmt)
     return false;
   struct Checker : DynamicRecursiveASTVisitor {
     const Stmt *DeadStmt;
-    bool CoroutineSubStmt = false;
-    Checker(const Stmt *S) : DeadStmt(S) {
-      // Statements captured in the CFG can be implicit.
-      ShouldVisitImplicitCode = true;
-    }
+    bool IsSubStmtOfTargetStmt = false;
+    Checker(const Stmt *S) : DeadStmt(S) { ShouldVisitImplicitCode = true; }
 
     bool VisitStmt(Stmt *S) override {
       if (S == DeadStmt)
-        CoroutineSubStmt = true;
+        IsSubStmtOfTargetStmt = true;
       return true;
     }
   };
   Checker checker(DeadStmt);
-  checker.TraverseStmt(const_cast<Stmt *>(CoroStmt));
-  return checker.CoroutineSubStmt;
+  checker.TraverseStmt(const_cast<Stmt *>(TargetStmt));
+  return checker.IsSubStmtOfTargetStmt;
 }
 
 static bool isValidDeadStmt(const Stmt *S, const clang::CFGBlock *Block) {
@@ -503,7 +499,12 @@ static bool isValidDeadStmt(const Stmt *S, const clang::CFGBlock *Block) {
   // Coroutine statements are never considered dead statements, because removing
   // them may change the function semantic if it is the only coroutine statement
   // of the coroutine.
-  return !isInCoroutineStmt(S, Block);
+  //
+  // If the dead stmt is a sub-stmt of CXXDefaultInitExpr and CXXDefaultArgExpr,
+  // we would rather expect to find CXXDefaultInitExpr and CXXDefaultArgExpr as
+  // a valid dead stmt.
+  return !isDeadStmtInOneOf<CoreturnStmt, CoroutineSuspendExpr,
+                            CXXDefaultArgExpr, CXXDefaultInitExpr>(S, Block);
 }
 
 const Stmt *DeadCodeScan::findDeadCode(const clang::CFGBlock *Block) {