[clang] [WIP][Clang] Extend lifetime of the temporary in default member init expression (PR #86960)

[via cfe-commits]

https://github.com/yronglin updated https://github.com/llvm/llvm-project/pull/86960

>From 107cf4fdda2680a3de4fd0cea6e9fc1eaaf5f8c7 Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Thu, 28 Mar 2024 22:02:16 +0800
Subject: [PATCH] [WIP][Clang] Extend lifetime of the temporary in default
 member init expression

Signed-off-by: yronglin <yronglin777 at gmail.com>
---
 clang/lib/Sema/SemaExpr.cpp |  9 ++++++---
 clang/lib/Sema/SemaInit.cpp | 27 ++++++++-------------------
 2 files changed, 14 insertions(+), 22 deletions(-)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 5f03b981428251..3c923d7c002feb 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -6372,7 +6372,7 @@ ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
   Expr *Init = nullptr;
 
   bool NestedDefaultChecking = isCheckingDefaultArgumentOrInitializer();
-
+  bool InLifetimeExtendingContext = isInLifetimeExtendingContext();
   EnterExpressionEvaluationContext EvalContext(
       *this, ExpressionEvaluationContext::PotentiallyEvaluated, Field);
 
@@ -6407,12 +6407,15 @@ ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
   ImmediateCallVisitor V(getASTContext());
   if (!NestedDefaultChecking)
     V.TraverseDecl(Field);
-  if (V.HasImmediateCalls) {
+  if (V.HasImmediateCalls || InLifetimeExtendingContext) {
     ExprEvalContexts.back().DelayedDefaultInitializationContext = {Loc, Field,
                                                                    CurContext};
     ExprEvalContexts.back().IsCurrentlyCheckingDefaultArgumentOrInitializer =
         NestedDefaultChecking;
-
+    // Pass down lifetime extending flag, and collect temporaries in
+    // CreateMaterializeTemporaryExpr when we rewrite the call argument.
+    keepInLifetimeExtendingContext();
+    keepInMaterializeTemporaryObjectContext();
     EnsureImmediateInvocationInDefaultArgs Immediate(*this);
     ExprResult Res;
     runWithSufficientStackSpace(Loc, [&] {
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index aa470adb30b47f..85baf52e1f074c 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -8052,11 +8052,7 @@ static void visitLocalsRetainedByInitializer(IndirectLocalPath &Path,
 enum PathLifetimeKind {
   /// Lifetime-extend along this path.
   Extend,
-  /// We should lifetime-extend, but we don't because (due to technical
-  /// limitations) we can't. This happens for default member initializers,
-  /// which we don't clone for every use, so we don't have a unique
-  /// MaterializeTemporaryExpr to update.
-  ShouldExtend,
+
   /// Do not lifetime extend along this path.
   NoExtend
 };
@@ -8067,9 +8063,7 @@ static PathLifetimeKind
 shouldLifetimeExtendThroughPath(const IndirectLocalPath &Path) {
   PathLifetimeKind Kind = PathLifetimeKind::Extend;
   for (auto Elem : Path) {
-    if (Elem.Kind == IndirectLocalPathEntry::DefaultInit)
-      Kind = PathLifetimeKind::ShouldExtend;
-    else if (Elem.Kind != IndirectLocalPathEntry::LambdaCaptureInit)
+    if (Elem.Kind != IndirectLocalPathEntry::LambdaCaptureInit)
       return PathLifetimeKind::NoExtend;
   }
   return Kind;
@@ -8182,6 +8176,12 @@ void Sema::checkInitializerLifetime(const InitializedEntity &Entity,
 
       switch (shouldLifetimeExtendThroughPath(Path)) {
       case PathLifetimeKind::Extend:
+
+        // If in a lifetime-extending context, delay extending action.
+        // e.g. Delayed lifetime extending until building for-range-stmt. 
+        if (isInLifetimeExtendingContext())
+          return true;
+
         // Update the storage duration of the materialized temporary.
         // FIXME: Rebuild the expression instead of mutating it.
         MTE->setExtendingDecl(ExtendingEntity->getDecl(),
@@ -8189,17 +8189,6 @@ void Sema::checkInitializerLifetime(const InitializedEntity &Entity,
         // Also visit the temporaries lifetime-extended by this initializer.
         return true;
 
-      case PathLifetimeKind::ShouldExtend:
-        // We're supposed to lifetime-extend the temporary along this path (per
-        // the resolution of DR1815), but we don't support that yet.
-        //
-        // FIXME: Properly handle this situation. Perhaps the easiest approach
-        // would be to clone the initializer expression on each use that would
-        // lifetime extend its temporaries.
-        Diag(DiagLoc, diag::warn_unsupported_lifetime_extension)
-            << RK << DiagRange;
-        break;
-
       case PathLifetimeKind::NoExtend:
         // If the path goes through the initialization of a variable or field,
         // it can't possibly reach a temporary created in this full-expression.