[clang] [clang] Fix dangling false positives for conditional operators. (PR #120233)

[Haojian Wu via cfe-commits]

https://github.com/hokein created https://github.com/llvm/llvm-project/pull/120233

Fixes https://github.com/llvm/llvm-project/issues/120206

>From 36697bc0bc4047257b2307b26fdb5c4343dee340 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Tue, 17 Dec 2024 14:28:00 +0100
Subject: [PATCH] [clang] Fix dangling false positives for conditional
 operators.

---
 clang/docs/ReleaseNotes.rst                   |  2 ++
 clang/lib/Sema/CheckExprLifetime.cpp          |  9 ++++++
 .../Sema/warn-lifetime-analysis-nocfg.cpp     | 29 +++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index befa411e882b4c..2fb14da05bbef5 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -677,6 +677,8 @@ Improvements to Clang's diagnostics
       views.push_back(std::string("123")); // warning
     }
 
+- Fix -Wdangling false positives on conditional operators (#120206).
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index 843fdb4a65cd73..e4eb7d66575bb9 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -582,6 +582,15 @@ static void visitFunctionCallArguments(IndirectLocalPath &Path, Expr *Call,
     //   Temp().ptr; // Here ptr might not dangle.
     if (isa<MemberExpr>(Arg->IgnoreImpCasts()))
       return;
+    // Avoid false positives when the object is constructed from a conditional
+    // operator argument. A common case is:
+    //   // 'ptr' might not be owned by the Owner object.
+    //   std::string_view s = cond() ? Owner().ptr : sv;
+    if (const auto *Cond =
+            dyn_cast<AbstractConditionalOperator>(Arg->IgnoreImpCasts());
+        Cond && isPointerLikeType(Cond->getType()))
+      return;
+
     auto ReturnType = Callee->getReturnType();
 
     // Once we initialized a value with a non gsl-owner reference, it can no
diff --git a/clang/test/Sema/warn-lifetime-analysis-nocfg.cpp b/clang/test/Sema/warn-lifetime-analysis-nocfg.cpp
index 45b4dc838f44ed..4c19367bb7f3dd 100644
--- a/clang/test/Sema/warn-lifetime-analysis-nocfg.cpp
+++ b/clang/test/Sema/warn-lifetime-analysis-nocfg.cpp
@@ -777,3 +777,32 @@ void test4() {
 }
 
 } // namespace LifetimeboundInterleave
+
+namespace GH120206 {
+struct S {
+  std::string_view s;
+};
+
+struct [[gsl::Owner]] Q1 {
+  const S* get() const [[clang::lifetimebound]];
+};
+std::string_view test1(int c, std::string_view sv) {
+  std::string_view k = c > 1 ? Q1().get()->s : sv;
+  if (c == 1)
+    return  c > 1 ? Q1().get()->s : sv;
+  Q1 q;
+  return c > 1 ? q.get()->s : sv;
+}
+
+struct Q2 {
+  const S* get() const [[clang::lifetimebound]];
+};
+std::string_view test2(int c, std::string_view sv) {
+  std::string_view k = c > 1 ? Q2().get()->s : sv;
+  if (c == 1)
+    return c > 1 ? Q2().get()->s : sv;
+  Q2 q;
+  return c > 1 ? q.get()->s : sv;
+}
+
+} // namespace GH120206