[clang] [clang] Fix lifetime extension of temporaries in for-range-initializers in templates (PR #177191)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (yronglin)

<details>
<summary>Changes</summary>

Fixes https://github.com/llvm/llvm-project/issues/165182.

This patch fix the lifetime extension of temporaries in for-range-initializers in templates. Whether this issue was occurred when the for-range statement in a dependent context, but itself is not type/value dependent.

---
Full diff: https://github.com/llvm/llvm-project/pull/177191.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaStmt.cpp (+7-8) 
- (modified) clang/test/CXX/special/class.temporary/p6.cpp (+34) 


``````````diff
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 1b1643250d05e..5ab10fdfc7b74 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2753,14 +2753,6 @@ StmtResult Sema::BuildCXXForRangeStmt(
                             diag::err_for_range_incomplete_type))
       return StmtError();
 
-    // P2718R0 - Lifetime extension in range-based for loops.
-    if (getLangOpts().CPlusPlus23 && !LifetimeExtendTemps.empty()) {
-      InitializedEntity Entity =
-          InitializedEntity::InitializeVariable(RangeVar);
-      for (auto *MTE : LifetimeExtendTemps)
-        MTE->setExtendingDecl(RangeVar, Entity.allocateManglingNumber());
-    }
-
     // Build auto __begin = begin-expr, __end = end-expr.
     // Divide by 2, since the variables are in the inner scope (loop body).
     const auto DepthStr = std::to_string(S->getDepth() / 2);
@@ -3017,6 +3009,13 @@ StmtResult Sema::BuildCXXForRangeStmt(
   if (getLangOpts().OpenMP >= 50 && BeginDeclStmt.isUsable())
     OpenMP().ActOnOpenMPLoopInitialization(ForLoc, BeginDeclStmt.get());
 
+  // P2718R0 - Lifetime extension in range-based for loops.
+  if (getLangOpts().CPlusPlus23 && !LifetimeExtendTemps.empty()) {
+    InitializedEntity Entity = InitializedEntity::InitializeVariable(RangeVar);
+    for (auto *MTE : LifetimeExtendTemps)
+      MTE->setExtendingDecl(RangeVar, Entity.allocateManglingNumber());
+  }
+
   return new (Context) CXXForRangeStmt(
       InitStmt, RangeDS, cast_or_null<DeclStmt>(BeginDeclStmt.get()),
       cast_or_null<DeclStmt>(EndDeclStmt.get()), NotEqExpr.get(),
diff --git a/clang/test/CXX/special/class.temporary/p6.cpp b/clang/test/CXX/special/class.temporary/p6.cpp
index 2b1b531b7172c..12e760b60e65b 100644
--- a/clang/test/CXX/special/class.temporary/p6.cpp
+++ b/clang/test/CXX/special/class.temporary/p6.cpp
@@ -700,4 +700,38 @@ void default_init2() {
   for (auto &&x : B{0}.a.arr) {}
 }
 } // namespace default_init
+
+namespace GH165182 {
+extern "C" int printf(const char *, ...);
+
+const char* s = "1";
+
+struct Foo {
+  int& x;
+  Foo(int& x) noexcept : x{x} {}
+  ~Foo() noexcept { x = 42; }
+  const char* begin() const noexcept { return s; }
+  const char* end() const noexcept { return s + 1; }
+};
+
+const Foo& f1(const Foo& t) noexcept { return t; }
+Foo g(int& x) noexcept { return Foo(x); }
+
+// Lifetime extension is missing!
+template <typename T>
+int test1() {
+    int x = 5;
+    int sum = 0;
+    // CHECK-CXX23: for.cond.cleanup:
+    // CHECK-CXX23-NEXT: call void @_ZN7P2718R08GH1651823FooD1Ev(
+    for (int _ : f1(g(x))) sum += x;
+    sum += x;
+    return sum;
+}
+
+int foo() {
+    printf("%i\n", test1<int>());
+}
+
+} // namespace GH165182
 } // namespace P2718R0

``````````

</details>


https://github.com/llvm/llvm-project/pull/177191