[clang] [Clang] Support lifetime extension of temporary created by aggregate initialization using a default member initializer (PR #87933)
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Sun Apr 7 10:42:48 PDT 2024
https://github.com/yronglin created https://github.com/llvm/llvm-project/pull/87933
This PR complete [DR1815](https://wg21.link/CWG1815) under the guidance of `FIXME` comments. And reuse `CXXDefaultInitExpr` rewrite machinery to clone the initializer expression on each use that would lifetime extend its temporaries.
>From 9fba6da7cb1ffbc7d46b69c6ac0cfd15a89c4b56 Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Mon, 8 Apr 2024 01:38:23 +0800
Subject: [PATCH] [Clang] Support lifetime extension of temporary created by
aggregate initialization using a default member initializer
Signed-off-by: yronglin <yronglin777 at gmail.com>
---
.../clang/Basic/DiagnosticSemaKinds.td | 6 ---
clang/lib/Sema/SemaExpr.cpp | 16 ++++----
clang/lib/Sema/SemaInit.cpp | 39 +++++++++++++------
.../Analysis/lifetime-extended-regions.cpp | 2 +-
clang/test/CXX/drs/dr16xx.cpp | 2 -
clang/test/CXX/drs/dr18xx.cpp | 5 +--
clang/test/CXX/special/class.temporary/p6.cpp | 20 ++++++++++
clang/test/SemaCXX/constexpr-default-arg.cpp | 4 +-
clang/test/SemaCXX/eval-crashes.cpp | 6 +--
9 files changed, 62 insertions(+), 38 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index a1dda2d2461c31..ba779e83d2afd4 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -10010,12 +10010,6 @@ def warn_new_dangling_initializer_list : Warning<
"the allocated initializer list}0 "
"will be destroyed at the end of the full-expression">,
InGroup<DanglingInitializerList>;
-def warn_unsupported_lifetime_extension : Warning<
- "lifetime extension of "
- "%select{temporary|backing array of initializer list}0 created "
- "by aggregate initialization using a default member initializer "
- "is not yet supported; lifetime of %select{temporary|backing array}0 "
- "will end at the end of the full-expression">, InGroup<Dangling>;
// For non-floating point, expressions of the form x == x or x != x
// should result in a warning, since these always evaluate to a constant.
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8db4fffeecfe35..b2e0f2a2a60113 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -6338,10 +6338,9 @@ ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
Res = Immediate.TransformInitializer(Param->getInit(),
/*NotCopy=*/false);
});
- if (Res.isInvalid())
- return ExprError();
- Res = ConvertParamDefaultArgument(Param, Res.get(),
- Res.get()->getBeginLoc());
+ if (Res.isUsable())
+ Res = ConvertParamDefaultArgument(Param, Res.get(),
+ Res.get()->getBeginLoc());
if (Res.isInvalid())
return ExprError();
Init = Res.get();
@@ -6377,7 +6376,7 @@ ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
Expr *Init = nullptr;
bool NestedDefaultChecking = isCheckingDefaultArgumentOrInitializer();
-
+ bool InLifetimeExtendingContext = isInLifetimeExtendingContext();
EnterExpressionEvaluationContext EvalContext(
*this, ExpressionEvaluationContext::PotentiallyEvaluated, Field);
@@ -6412,11 +6411,14 @@ 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();
EnsureImmediateInvocationInDefaultArgs Immediate(*this);
ExprResult Res;
@@ -6424,7 +6426,7 @@ ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
Res = Immediate.TransformInitializer(Field->getInClassInitializer(),
/*CXXDirectInit=*/false);
});
- if (!Res.isInvalid())
+ if (Res.isUsable())
Res = ConvertMemberDefaultInitExpression(Field, Res.get(), Loc);
if (Res.isInvalid()) {
Field->setInvalidDecl();
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index a75e9925a43146..842412cd674d8c 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -710,6 +710,26 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
if (VerifyOnly)
return;
+ // Enter a lifetime extension context, then we can support lifetime
+ // extension of temporary created by aggregate initialization using a
+ // default member initializer (DR1815 https://wg21.link/CWG1815).
+ //
+ // In a lifetime extension context, BuildCXXDefaultInitExpr will clone the
+ // initializer expression on each use that would lifetime extend its
+ // temporaries.
+ EnterExpressionEvaluationContext LifetimeExtensionContext(
+ SemaRef, Sema::ExpressionEvaluationContext::PotentiallyEvaluated,
+ /*LambdaContextDecl=*/nullptr,
+ Sema::ExpressionEvaluationContextRecord::EK_Other, true);
+
+ // Lifetime extension in default-member-init.
+ auto &LastRecord = SemaRef.ExprEvalContexts.back();
+
+ // Just copy previous record, make sure we haven't forget anything.
+ LastRecord =
+ SemaRef.ExprEvalContexts[SemaRef.ExprEvalContexts.size() - 2];
+ LastRecord.InLifetimeExtendingContext = true;
+
ExprResult DIE = SemaRef.BuildCXXDefaultInitExpr(Loc, Field);
if (DIE.isInvalid()) {
hadError = true;
@@ -7699,6 +7719,8 @@ static void visitLocalsRetainedByReferenceBinding(IndirectLocalPath &Path,
// Step into CXXDefaultInitExprs so we can diagnose cases where a
// constructor inherits one as an implicit mem-initializer.
if (auto *DIE = dyn_cast<CXXDefaultInitExpr>(Init)) {
+ assert(DIE->hasRewrittenInit() &&
+ "CXXDefaultInitExpr must has rewritten init");
Path.push_back(
{IndirectLocalPathEntry::DefaultInit, DIE, DIE->getField()});
Init = DIE->getExpr();
@@ -8193,6 +8215,11 @@ void Sema::checkInitializerLifetime(const InitializedEntity &Entity,
}
switch (shouldLifetimeExtendThroughPath(Path)) {
+ case PathLifetimeKind::ShouldExtend:
+ // We're supposed to lifetime-extend the temporary along this path (per
+ // the resolution of DR1815), we supported that by clone the initializer
+ // expression on each use that would lifetime extend its temporaries.
+ [[fallthrough]];
case PathLifetimeKind::Extend:
// Update the storage duration of the materialized temporary.
// FIXME: Rebuild the expression instead of mutating it.
@@ -8200,18 +8227,6 @@ void Sema::checkInitializerLifetime(const InitializedEntity &Entity,
ExtendingEntity->allocateManglingNumber());
// 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.
diff --git a/clang/test/Analysis/lifetime-extended-regions.cpp b/clang/test/Analysis/lifetime-extended-regions.cpp
index 4e98bd4b0403eb..8df9b8a54a7e02 100644
--- a/clang/test/Analysis/lifetime-extended-regions.cpp
+++ b/clang/test/Analysis/lifetime-extended-regions.cpp
@@ -122,7 +122,7 @@ void aggregateWithReferences() {
clang_analyzer_dump(viaReference.ry); // expected-warning-re {{&lifetime_extended_object{Composite, viaReference, S{{[0-9]+}}} }}
// clang does not currently implement extending lifetime of object bound to reference members of aggregates,
- // that are created from default member initializer (see `warn_unsupported_lifetime_extension` from `-Wdangling`)
+ // that are created from default member initializer (see `warn_unsupported_lifetime_extension` from `-Wdangling`) (Supported now).
RefAggregate defaultInitExtended{i}; // clang-bug does not extend `Composite`
clang_analyzer_dump(defaultInitExtended.ry); // expected-warning {{Unknown }}
}
diff --git a/clang/test/CXX/drs/dr16xx.cpp b/clang/test/CXX/drs/dr16xx.cpp
index f4d6c04fb8e073..52002a7d0db002 100644
--- a/clang/test/CXX/drs/dr16xx.cpp
+++ b/clang/test/CXX/drs/dr16xx.cpp
@@ -484,8 +484,6 @@ namespace dr1696 { // dr1696: 7
const A &a = A(); // #dr1696-D1-a
};
D1 d1 = {}; // #dr1696-d1
- // since-cxx14-warning at -1 {{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported; lifetime of temporary will end at the end of the full-expression}}
- // since-cxx14-note@#dr1696-D1-a {{initializing field 'a' with default member initializer}}
struct D2 {
const A &a = A(); // #dr1696-D2-a
diff --git a/clang/test/CXX/drs/dr18xx.cpp b/clang/test/CXX/drs/dr18xx.cpp
index e78730e8992cf8..52a90ea3a05d26 100644
--- a/clang/test/CXX/drs/dr18xx.cpp
+++ b/clang/test/CXX/drs/dr18xx.cpp
@@ -206,13 +206,10 @@ namespace dr1814 { // dr1814: yes
#endif
}
-namespace dr1815 { // dr1815: no
+namespace dr1815 { // dr1815: yes
#if __cplusplus >= 201402L
- // FIXME: needs codegen test
struct A { int &&r = 0; }; // #dr1815-A
A a = {};
- // since-cxx14-warning at -1 {{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported; lifetime of temporary will end at the end of the full-expression}} FIXME
- // since-cxx14-note@#dr1815-A {{initializing field 'r' with default member initializer}}
struct B { int &&r = 0; }; // #dr1815-B
// since-cxx14-error at -1 {{reference member 'r' binds to a temporary object whose lifetime would be shorter than the lifetime of the constructed object}}
diff --git a/clang/test/CXX/special/class.temporary/p6.cpp b/clang/test/CXX/special/class.temporary/p6.cpp
index 5554363cc69abb..002bf3e1c26740 100644
--- a/clang/test/CXX/special/class.temporary/p6.cpp
+++ b/clang/test/CXX/special/class.temporary/p6.cpp
@@ -269,6 +269,26 @@ void init_capture_init_list() {
// CHECK: }
}
+void check_dr1815() { // dr1815: yes
+#if __cplusplus >= 201402L
+
+ struct A {
+ int &&r = 0;
+ ~A() {}
+ };
+
+ struct B {
+ A &&a = A{};
+ ~B() {}
+ };
+
+ // CHECK: void @_Z12check_dr1815v()
+ // CHECK: call void @_ZZ12check_dr1815vEN1BD1Ev(
+ // CHECK: call void @_ZZ12check_dr1815vEN1AD1Ev(
+ B a = {};
+#endif
+}
+
namespace P2718R0 {
namespace basic {
template <typename E> using T2 = std::list<E>;
diff --git a/clang/test/SemaCXX/constexpr-default-arg.cpp b/clang/test/SemaCXX/constexpr-default-arg.cpp
index 7c883692829548..8510a6ddc80399 100644
--- a/clang/test/SemaCXX/constexpr-default-arg.cpp
+++ b/clang/test/SemaCXX/constexpr-default-arg.cpp
@@ -32,8 +32,8 @@ void test_default_arg2() {
}
// Check that multiple CXXDefaultInitExprs don't cause an assertion failure.
-struct A { int &&r = 0; }; // expected-note 2{{default member initializer}}
+struct A { int &&r = 0; };
struct B { A x, y; };
-B b = {}; // expected-warning 2{{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported}}
+B b = {}; // expected-no-diagnostics
}
diff --git a/clang/test/SemaCXX/eval-crashes.cpp b/clang/test/SemaCXX/eval-crashes.cpp
index 017df977b26b7b..a06f60f71e9c7e 100644
--- a/clang/test/SemaCXX/eval-crashes.cpp
+++ b/clang/test/SemaCXX/eval-crashes.cpp
@@ -25,11 +25,9 @@ namespace pr33140_0b {
}
namespace pr33140_2 {
- // FIXME: The declaration of 'b' below should lifetime-extend two int
- // temporaries.
- struct A { int &&r = 0; }; // expected-note 2{{initializing field 'r' with default member initializer}}
+ struct A { int &&r = 0; };
struct B { A x, y; };
- B b = {}; // expected-warning 2{{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported}}
+ B b = {};
}
namespace pr33140_3 {
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