[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
mrcvtl wrote:
A couple of quick notes:
- This is my first LLVM PR, so if there are any issues with code style or
conventions, please let me know!
- I'm not entirely satisfied with the `VD->getName().starts_with("__range")`
check, but it was the most reliable approach I found. Walking up the AST from
the node didn’t seem feasible (likely due to optimizations?) and I noticed that
pattern here:
https://github.com/llvm/llvm-project/blob/075cb691a5e810f7114369c67b475dfd9127d4af/clang/lib/Sema/SemaStmt.cpp#L2481-L2485
https://github.com/llvm/llvm-project/pull/145164
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[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl ready_for_review https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
mrcvtl wrote: I’ve taken some time to better understand the code and think through the solution. I tried using `isInLifetimeExtendingContext()`, but it still returns false, and I believe I now understand why. In your PR, the flag is set here: https://github.com/llvm/llvm-project/blob/b581f9d056babadf55098b9d5d100271621b90db/clang/lib/Parse/ParseDecl.cpp#L2314-L2318 However, the warning is actually triggered starting from this location: https://github.com/llvm/llvm-project/blob/b581f9d056babadf55098b9d5d100271621b90db/clang/lib/Parse/ParseDecl.cpp#L2266 An alternative approach to apply your logic and set again the flag in here: https://github.com/llvm/llvm-project/blob/43d042b350af8ee8c7401d6b102df68d6c176b5a/clang/lib/Parse/ParseStmt.cpp#L2174-L2179 Maybe we could act on `ForRangeInfo.LifetimeExtendTemps.back()`, or even directly on `Actions.currentEvaluationContext();`. If that works, we might be able to rely solely on `isInLifetimeExtendingContext()` and remove the need for `isRangeBasedForLoopVariable` altogether. What do you think? I'm absolutely open to every approach (the cleaner, the better!). https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
mrcvtl wrote: > Could you associate this PR with the issue to fix, if any? Done! https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl edited https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl created
https://github.com/llvm/llvm-project/pull/145164
C++23 mandates that temporaries used in range-based for loops are
lifetime-extended
to cover the full loop. This patch adds a check for loop variables and compiler-
generated `__range` bindings to apply the correct extension.
Includes test cases based on examples from CWG900/P2644R1.
>From 4398de927292be66f8f54c93c1064b6230f5470a Mon Sep 17 00:00:00 2001
From: Marco Vitale
Date: Sat, 21 Jun 2025 14:01:53 +0200
Subject: [PATCH] [Sema] Fix lifetime extension for temporaries in range-based
for loops in C++23
C++23 mandates that temporaries used in range-based for loops are
lifetime-extended
to cover the full loop. This patch adds a check for loop variables and compiler-
generated `__range` bindings to apply the correct extension.
Includes test cases based on examples from CWG900/P2644R1.
---
clang/lib/Sema/CheckExprLifetime.cpp | 28 +++
.../test/SemaCXX/range-for-lifetime-cxx23.cpp | 79 +++
2 files changed, 107 insertions(+)
create mode 100644 clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
diff --git a/clang/lib/Sema/CheckExprLifetime.cpp
b/clang/lib/Sema/CheckExprLifetime.cpp
index 060ba31660556..0434aa0c29c26 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -57,6 +57,31 @@ enum LifetimeKind {
};
using LifetimeResult =
llvm::PointerIntPair;
+
+/// Returns true if the given entity is part of a range-based for loop and
+/// should trigger lifetime extension under C++23 rules.
+///
+/// This handles both explicit range loop variables and internal compiler-
+/// generated variables like `__range1`.
+static bool
+isRangeBasedForLoopVariable(const Sema &SemaRef,
+const InitializedEntity *ExtendingEntity) {
+ if (!SemaRef.getLangOpts().CPlusPlus23)
+return false;
+
+ const Decl *EntityDecl = ExtendingEntity->getDecl();
+ if (!EntityDecl)
+return false;
+
+ if (const auto *VD = dyn_cast(EntityDecl)) {
+if (VD->isCXXForRangeDecl() || VD->getName().starts_with("__range")) {
+ return true;
+}
+ }
+
+ return false;
+}
+
} // namespace
/// Determine the declaration which an initialized entity ultimately refers to,
@@ -1341,6 +1366,9 @@ checkExprLifetimeImpl(Sema &SemaRef, const
InitializedEntity *InitEntity,
}
if (IsGslPtrValueFromGslTempOwner && DiagLoc.isValid()) {
+if (isRangeBasedForLoopVariable(SemaRef, ExtendingEntity))
+ return true;
+
SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
<< DiagRange;
return false;
diff --git a/clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
b/clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
new file mode 100644
index 0..bb6e06ec4517c
--- /dev/null
+++ b/clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
@@ -0,0 +1,79 @@
+// RUN: %clangxx -std=c++23 -fsyntax-only -Xclang -verify %s
+
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+
+static std::vector getVector() {
+ return {"first", "second", "third"};
+}
+
+static std::map> getMap() {
+ return {{"key", {1, 2, 3}}};
+}
+
+static std::tuple> getTuple() {
+ return std::make_tuple(std::vector{3.14, 2.71});
+}
+
+static std::optional> getOptionalColl() {
+ return std::vector{'x', 'y', 'z'};
+}
+
+static std::variant getVariant() {
+ return std::string("variant");
+}
+
+static const std::array& arrOfConst() {
+ static const std::array arr = {10, 20, 30, 40};
+ return arr;
+}
+
+static void testGetVectorSubscript() {
+ for (auto e : getVector()[0]) {
+(void)e;
+ }
+}
+
+static void testGetMapSubscript() {
+ for (auto valueElem : getMap()["key"]) {
+(void)valueElem;
+ }
+}
+
+static void testGetTuple() {
+ for (auto e : std::get<0>(getTuple())) {
+(void)e;
+ }
+}
+
+static void testOptionalValue() {
+ for (auto e : getOptionalColl().value()) {
+(void)e;
+ }
+}
+
+static void testVariantGetString() {
+ for (char c : std::get(getVariant())) {
+(void)c;
+ }
+}
+
+static void testSpanLastFromConstArray() {
+ for (auto s : std::span{arrOfConst()}.last(2)) {
+(void)s;
+ }
+}
+
+static void testSpanFromVectorPtr() {
+ for (auto e : std::span(getVector().data(), 2)) {
+(void)e;
+ }
+}
+
+// expected-no-diagnostics
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[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
mrcvtl wrote:
> IMO, we have 2 options:
>
> 1. Add a flag variable into `ExpressionEvaluationContextRecord`. Represent
> that we are initializing the for-range __range variable.
>Eg.
>
> ```diff
> diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
> index 9397546c8fc5..c639a4b4af58 100644
> --- a/clang/include/clang/Sema/Sema.h
> +++ b/clang/include/clang/Sema/Sema.h
> @@ -6786,6 +6786,9 @@ public:
> /// Whether we should rebuild CXXDefaultArgExpr and CXXDefaultInitExpr.
> bool RebuildDefaultArgOrDefaultInit = false;
>
> +/// Whether we are initializing a C++ for-range implicit variable
> '__range'.
> +bool InitCXXForRangeVar = false;
> +
> // When evaluating immediate functions in the initializer of a default
> // argument or default member initializer, this is the declaration whose
> // default initializer is being evaluated and the location of the call
> diff --git a/clang/lib/Sema/CheckExprLifetime.cpp
> b/clang/lib/Sema/CheckExprLifetime.cpp
> index 060ba3166055..150e27f8acf7 100644
> --- a/clang/lib/Sema/CheckExprLifetime.cpp
> +++ b/clang/lib/Sema/CheckExprLifetime.cpp
> @@ -1341,6 +1341,8 @@ checkExprLifetimeImpl(Sema &SemaRef, const
> InitializedEntity *InitEntity,
>}
>
>if (IsGslPtrValueFromGslTempOwner && DiagLoc.isValid()) {
> +if (SemaRef.currentEvaluationContext().InitCXXForRangeVar)
> + return false;
> SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
> << DiagRange;
> return false;
> diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
> index 923a9e81fbd6..da97d34854ac 100644
> --- a/clang/lib/Sema/SemaStmt.cpp
> +++ b/clang/lib/Sema/SemaStmt.cpp
> @@ -2374,6 +2374,13 @@ static bool FinishForRangeVarDecl(Sema &SemaRef,
> VarDecl *Decl, Expr *Init,
>SemaRef.ObjC().inferObjCARCLifetime(Decl))
> Decl->setInvalidDecl();
>
> + // EnterExpressionEvaluationContext ForRangeInitContext(
> + // SemaRef, Sema::ExpressionEvaluationContext::PotentiallyEvaluated,
> + // /*LambdaContextDecl=*/nullptr,
> + // Sema::ExpressionEvaluationContextRecord::EK_Other,
> + // SemaRef.getLangOpts().CPlusPlus23);
> + if (SemaRef.getLangOpts().CPlusPlus23)
> +SemaRef.currentEvaluationContext().InitCXXForRangeVar = true;
>SemaRef.AddInitializerToDecl(Decl, Init, /*DirectInit=*/false);
>SemaRef.FinalizeDeclaration(Decl);
>SemaRef.CurContext->addHiddenDecl(Decl);
> ```
>
> 2. Introduce a bitfields into `clang::VarDecl::NonParmVarDeclBitfields`, like
> `CXXForRangeDecl`(Eg. `CXXForRangeImplicitVar`)
>
> CC @cor3ntin
I like option one! Maybe a stupid question, but why can’t we use
`InLifetimeExtendingContext` flag here? It feels like it’s meant to capture the
same kind of situation. Is there a subtle difference I’m missing?
I updated (locally) the PR to address the other feedbacks and I will push when
I have the green light to use option 1!
https://github.com/llvm/llvm-project/pull/145164
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[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl updated
https://github.com/llvm/llvm-project/pull/145164
>From b5146278ce5059b6bf0312f18f509022de5fd661 Mon Sep 17 00:00:00 2001
From: Marco Vitale
Date: Sat, 21 Jun 2025 14:01:53 +0200
Subject: [PATCH 1/2] [Sema] Fix lifetime extension for temporaries in
range-based for loops in C++23
C++23 mandates that temporaries used in range-based for loops are
lifetime-extended
to cover the full loop. This patch adds a check for loop variables and compiler-
generated `__range` bindings to apply the correct extension.
Includes test cases based on examples from CWG900/P2644R1.
---
clang/docs/ReleaseNotes.rst | 4 +++
clang/lib/Sema/CheckExprLifetime.cpp | 5
clang/lib/Sema/SemaStmt.cpp | 3 +++
.../test/SemaCXX/range-for-lifetime-cxx23.cpp | 27 +++
4 files changed, 39 insertions(+)
create mode 100644 clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index d9847fadc21e5..d79df8c9184be 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -648,6 +648,10 @@ Improvements to Clang's diagnostics
#GH142457, #GH139913, #GH138850, #GH137867, #GH137860, #GH107840, #GH93308,
#GH69470, #GH59391, #GH58172, #GH46215, #GH45915, #GH45891, #GH44490,
#GH36703, #GH32903, #GH23312, #GH69874.
+
+- Clang no longer emits a spurious -Wdangling-gsl warning in C++23 when
+ iterating over an element of a temporary container in a range-based
+ for loop.(#GH109793, #GH145164)
- Clang now avoids issuing `-Wreturn-type` warnings in some cases where
the final statement of a non-void function is a `throw` expression, or
diff --git a/clang/lib/Sema/CheckExprLifetime.cpp
b/clang/lib/Sema/CheckExprLifetime.cpp
index 060ba31660556..114e4f989ed9f 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -57,6 +57,7 @@ enum LifetimeKind {
};
using LifetimeResult =
llvm::PointerIntPair;
+
} // namespace
/// Determine the declaration which an initialized entity ultimately refers to,
@@ -1341,6 +1342,10 @@ checkExprLifetimeImpl(Sema &SemaRef, const
InitializedEntity *InitEntity,
}
if (IsGslPtrValueFromGslTempOwner && DiagLoc.isValid()) {
+if (SemaRef.getLangOpts().CPlusPlus23 &&
+SemaRef.isInLifetimeExtendingContext())
+ return false;
+
SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
<< DiagRange;
return false;
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 923a9e81fbd6a..633f73946b729 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2374,6 +2374,9 @@ static bool FinishForRangeVarDecl(Sema &SemaRef, VarDecl
*Decl, Expr *Init,
SemaRef.ObjC().inferObjCARCLifetime(Decl))
Decl->setInvalidDecl();
+ if (SemaRef.getLangOpts().CPlusPlus23)
+SemaRef.currentEvaluationContext().InLifetimeExtendingContext = true;
+
SemaRef.AddInitializerToDecl(Decl, Init, /*DirectInit=*/false);
SemaRef.FinalizeDeclaration(Decl);
SemaRef.CurContext->addHiddenDecl(Decl);
diff --git a/clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
b/clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
new file mode 100644
index 0..c36fd6c246347
--- /dev/null
+++ b/clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+
+using size_t = decltype(sizeof(void *));
+
+namespace std {
+template struct vector {
+ T &operator[](size_t I);
+};
+
+struct string {
+ const char *begin();
+ const char *end();
+};
+
+} // namespace std
+
+std::vector getData();
+
+void foo() {
+ // Verifies we don't trigger a diagnostic from -Wdangling-gsl
+ // when iterating over a temporary in C++23.
+ for (auto c : getData()[0]) {
+(void)c;
+ }
+}
+
+// expected-no-diagnostics
>From b2e1333c2b9e61ffb8b85d1613c137f8f96a73e4 Mon Sep 17 00:00:00 2001
From: Marco Vitale
Date: Sat, 28 Jun 2025 00:25:33 +0200
Subject: [PATCH 2/2] Add as a flag in VarDecl
---
clang/include/clang/AST/Decl.h| 19 +++
clang/lib/Sema/CheckExprLifetime.cpp | 9 ++---
clang/lib/Sema/SemaStmt.cpp | 1 +
clang/lib/Serialization/ASTReaderDecl.cpp | 1 +
clang/lib/Serialization/ASTWriterDecl.cpp | 2 ++
5 files changed, 29 insertions(+), 3 deletions(-)
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index c4202f1f3d07e..eee925b01d9e8 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -1086,6 +1086,11 @@ class VarDecl : public DeclaratorDecl, public
Redeclarable {
LLVM_PREFERRED_TYPE(bool)
unsigned IsCXXCondDecl : 1;
+
+/// Whether this variable is the implicit __range variable in a for-range
+/// loop.
+LLVM_PREFERRED_TYPE(bool)
+unsigned IsCXXForRangeImplicitVar : 1;
};
union {
@@ -1585
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
mrcvtl wrote: > > but why can’t we use InLifetimeExtendingContext flag here? > > Is there a subtle difference I’m missing? > > This flag will tiger subroutines to collect `MaterializedTemporaryExpr` and > rebuild default init/arg。 All we need to know here is that `ExtendingDecl` is > a C++ `__range` var in for-range-loop, so I think we should introduce a new > flag in VarDecl. We may need to also modify handling of VarDecl in ASTWriter > and ASTReader to ensure that the AST serialization is correct. WDYT? Agreed. My last commit should implement this. Let me know if something is wrong! https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
@@ -2740,6 +2741,7 @@ void ASTWriter::WriteDeclAbbrevs() {
// isInline, isInlineSpecified, isConstexpr,
// isInitCapture, isPrevDeclInSameScope, hasInitWithSideEffects,
// EscapingByref, HasDeducedType, ImplicitParamKind, isObjCForDecl
+// isCXXForRangeDecl
mrcvtl wrote:
This should be `IsCXXForRangeImplicitVar`
https://github.com/llvm/llvm-project/pull/145164
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[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
@@ -1585,6 +1590,20 @@ class VarDecl : public DeclaratorDecl, public
Redeclarable {
NonParmVarDeclBits.IsCXXCondDecl = true;
}
+ /// Determine whether this variable is the compiler-generated '__range'
+ /// variable used to hold the range expression in a C++11 and later for-range
+ /// statement.
+ bool isCXXForRangeImplicitVar() const {
+return isa(this) ? false
+ :
NonParmVarDeclBits.IsCXXForRangeImplicitVar;
+ }
+
+ void setCXXForRangeImplicitVar(bool FRV) {
+assert(!isa(this) &&
+ "Cannot set IsCXXForRangeRangeVar on ParmVarDecl");
mrcvtl wrote:
Also here should be `Cannot set IsCXXForRangeRangeVar...`.
https://github.com/llvm/llvm-project/pull/145164
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[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl deleted https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl deleted https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl updated
https://github.com/llvm/llvm-project/pull/145164
>From 37c57131c397d4aeaef7fe5b860d1983f1e4bdc2 Mon Sep 17 00:00:00 2001
From: Marco Vitale
Date: Sat, 21 Jun 2025 14:01:53 +0200
Subject: [PATCH] [Sema] Fix lifetime extension for temporaries in range-based
for loops in C++23
C++23 mandates that temporaries used in range-based for loops are
lifetime-extended
to cover the full loop. This patch adds a check for loop variables and compiler-
generated `__range` bindings to apply the correct extension.
Includes test cases based on examples from CWG900/P2644R1.
---
clang/docs/ReleaseNotes.rst | 4 +++
clang/include/clang/AST/Decl.h| 19 +
clang/lib/Sema/CheckExprLifetime.cpp | 8 ++
clang/lib/Sema/SemaStmt.cpp | 4 +++
clang/lib/Serialization/ASTReaderDecl.cpp | 1 +
clang/lib/Serialization/ASTWriterDecl.cpp | 2 ++
.../test/SemaCXX/range-for-lifetime-cxx23.cpp | 27 +++
7 files changed, 65 insertions(+)
create mode 100644 clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 89d86c3371247..184d1f0b188be 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -643,6 +643,10 @@ Improvements to Clang's diagnostics
#GH142457, #GH139913, #GH138850, #GH137867, #GH137860, #GH107840, #GH93308,
#GH69470, #GH59391, #GH58172, #GH46215, #GH45915, #GH45891, #GH44490,
#GH36703, #GH32903, #GH23312, #GH69874.
+
+- Clang no longer emits a spurious -Wdangling-gsl warning in C++23 when
+ iterating over an element of a temporary container in a range-based
+ for loop.(#GH109793, #GH145164)
Improvements to Clang's time-trace
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index 0da940883b6f5..ab23346cc2fad 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -1085,6 +1085,11 @@ class VarDecl : public DeclaratorDecl, public
Redeclarable {
LLVM_PREFERRED_TYPE(bool)
unsigned IsCXXCondDecl : 1;
+
+/// Whether this variable is the implicit __range variable in a for-range
+/// loop.
+LLVM_PREFERRED_TYPE(bool)
+unsigned IsCXXForRangeImplicitVar : 1;
};
union {
@@ -1584,6 +1589,20 @@ class VarDecl : public DeclaratorDecl, public
Redeclarable {
NonParmVarDeclBits.IsCXXCondDecl = true;
}
+ /// Determine whether this variable is the compiler-generated '__range'
+ /// variable used to hold the range expression in a C++11 and later for-range
+ /// statement.
+ bool isCXXForRangeImplicitVar() const {
+return isa(this) ? false
+ :
NonParmVarDeclBits.IsCXXForRangeImplicitVar;
+ }
+
+ void setCXXForRangeImplicitVar(bool FRV) {
+assert(!isa(this) &&
+ "Cannot set IsCXXForRangeImplicitVar on ParmVarDecl");
+NonParmVarDeclBits.IsCXXForRangeImplicitVar = FRV;
+ }
+
/// Determines if this variable's alignment is dependent.
bool hasDependentAlignment() const;
diff --git a/clang/lib/Sema/CheckExprLifetime.cpp
b/clang/lib/Sema/CheckExprLifetime.cpp
index 060ba31660556..fc52de1e6bd89 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -57,6 +57,7 @@ enum LifetimeKind {
};
using LifetimeResult =
llvm::PointerIntPair;
+
} // namespace
/// Determine the declaration which an initialized entity ultimately refers to,
@@ -1341,6 +1342,13 @@ checkExprLifetimeImpl(Sema &SemaRef, const
InitializedEntity *InitEntity,
}
if (IsGslPtrValueFromGslTempOwner && DiagLoc.isValid()) {
+
+if (SemaRef.getLangOpts().CPlusPlus23) {
+ if (const VarDecl *VD = cast(InitEntity->getDecl());
+ VD && VD->isCXXForRangeImplicitVar())
+return false;
+}
+
SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
<< DiagRange;
return false;
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 923a9e81fbd6a..ef0aff1b2838f 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2374,6 +2374,9 @@ static bool FinishForRangeVarDecl(Sema &SemaRef, VarDecl
*Decl, Expr *Init,
SemaRef.ObjC().inferObjCARCLifetime(Decl))
Decl->setInvalidDecl();
+ if (SemaRef.getLangOpts().CPlusPlus23)
+SemaRef.currentEvaluationContext().InLifetimeExtendingContext = true;
+
SemaRef.AddInitializerToDecl(Decl, Init, /*DirectInit=*/false);
SemaRef.FinalizeDeclaration(Decl);
SemaRef.CurContext->addHiddenDecl(Decl);
@@ -2423,6 +2426,7 @@ VarDecl *BuildForRangeVarDecl(Sema &SemaRef,
SourceLocation Loc,
VarDecl *Decl = VarDecl::Create(SemaRef.Context, DC, Loc, Loc, II, Type,
TInfo, SC_None);
Decl->setImplicit();
+ Decl->setCXXForRangeImplicitVar(true);
return Decl;
}
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
https://github.com/mrcvtl updated
https://github.com/llvm/llvm-project/pull/145164
>From 37c57131c397d4aeaef7fe5b860d1983f1e4bdc2 Mon Sep 17 00:00:00 2001
From: Marco Vitale
Date: Sat, 21 Jun 2025 14:01:53 +0200
Subject: [PATCH 1/2] [Sema] Fix lifetime extension for temporaries in
range-based for loops in C++23
C++23 mandates that temporaries used in range-based for loops are
lifetime-extended
to cover the full loop. This patch adds a check for loop variables and compiler-
generated `__range` bindings to apply the correct extension.
Includes test cases based on examples from CWG900/P2644R1.
---
clang/docs/ReleaseNotes.rst | 4 +++
clang/include/clang/AST/Decl.h| 19 +
clang/lib/Sema/CheckExprLifetime.cpp | 8 ++
clang/lib/Sema/SemaStmt.cpp | 4 +++
clang/lib/Serialization/ASTReaderDecl.cpp | 1 +
clang/lib/Serialization/ASTWriterDecl.cpp | 2 ++
.../test/SemaCXX/range-for-lifetime-cxx23.cpp | 27 +++
7 files changed, 65 insertions(+)
create mode 100644 clang/test/SemaCXX/range-for-lifetime-cxx23.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 89d86c3371247..184d1f0b188be 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -643,6 +643,10 @@ Improvements to Clang's diagnostics
#GH142457, #GH139913, #GH138850, #GH137867, #GH137860, #GH107840, #GH93308,
#GH69470, #GH59391, #GH58172, #GH46215, #GH45915, #GH45891, #GH44490,
#GH36703, #GH32903, #GH23312, #GH69874.
+
+- Clang no longer emits a spurious -Wdangling-gsl warning in C++23 when
+ iterating over an element of a temporary container in a range-based
+ for loop.(#GH109793, #GH145164)
Improvements to Clang's time-trace
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index 0da940883b6f5..ab23346cc2fad 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -1085,6 +1085,11 @@ class VarDecl : public DeclaratorDecl, public
Redeclarable {
LLVM_PREFERRED_TYPE(bool)
unsigned IsCXXCondDecl : 1;
+
+/// Whether this variable is the implicit __range variable in a for-range
+/// loop.
+LLVM_PREFERRED_TYPE(bool)
+unsigned IsCXXForRangeImplicitVar : 1;
};
union {
@@ -1584,6 +1589,20 @@ class VarDecl : public DeclaratorDecl, public
Redeclarable {
NonParmVarDeclBits.IsCXXCondDecl = true;
}
+ /// Determine whether this variable is the compiler-generated '__range'
+ /// variable used to hold the range expression in a C++11 and later for-range
+ /// statement.
+ bool isCXXForRangeImplicitVar() const {
+return isa(this) ? false
+ :
NonParmVarDeclBits.IsCXXForRangeImplicitVar;
+ }
+
+ void setCXXForRangeImplicitVar(bool FRV) {
+assert(!isa(this) &&
+ "Cannot set IsCXXForRangeImplicitVar on ParmVarDecl");
+NonParmVarDeclBits.IsCXXForRangeImplicitVar = FRV;
+ }
+
/// Determines if this variable's alignment is dependent.
bool hasDependentAlignment() const;
diff --git a/clang/lib/Sema/CheckExprLifetime.cpp
b/clang/lib/Sema/CheckExprLifetime.cpp
index 060ba31660556..fc52de1e6bd89 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -57,6 +57,7 @@ enum LifetimeKind {
};
using LifetimeResult =
llvm::PointerIntPair;
+
} // namespace
/// Determine the declaration which an initialized entity ultimately refers to,
@@ -1341,6 +1342,13 @@ checkExprLifetimeImpl(Sema &SemaRef, const
InitializedEntity *InitEntity,
}
if (IsGslPtrValueFromGslTempOwner && DiagLoc.isValid()) {
+
+if (SemaRef.getLangOpts().CPlusPlus23) {
+ if (const VarDecl *VD = cast(InitEntity->getDecl());
+ VD && VD->isCXXForRangeImplicitVar())
+return false;
+}
+
SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
<< DiagRange;
return false;
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 923a9e81fbd6a..ef0aff1b2838f 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2374,6 +2374,9 @@ static bool FinishForRangeVarDecl(Sema &SemaRef, VarDecl
*Decl, Expr *Init,
SemaRef.ObjC().inferObjCARCLifetime(Decl))
Decl->setInvalidDecl();
+ if (SemaRef.getLangOpts().CPlusPlus23)
+SemaRef.currentEvaluationContext().InLifetimeExtendingContext = true;
+
SemaRef.AddInitializerToDecl(Decl, Init, /*DirectInit=*/false);
SemaRef.FinalizeDeclaration(Decl);
SemaRef.CurContext->addHiddenDecl(Decl);
@@ -2423,6 +2426,7 @@ VarDecl *BuildForRangeVarDecl(Sema &SemaRef,
SourceLocation Loc,
VarDecl *Decl = VarDecl::Create(SemaRef.Context, DC, Loc, Loc, II, Type,
TInfo, SC_None);
Decl->setImplicit();
+ Decl->setCXXForRangeImplicitVar(true);
return Decl;
}
diff --git a/clang/lib/Serialization/ASTReaderDecl.c
[clang] [Sema] Fix lifetime extension for temporaries in range-based for loops in C++23 (PR #145164)
mrcvtl wrote: Old clang tidy test failing seems flaky, locally builds correctly. If it continue to fail I can rebase on upstream. https://github.com/llvm/llvm-project/pull/145164 ___ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
