[clang] [Clang] Remove workaround for libstdc++4.7 (PR #139693)
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Tue May 13 22:54:22 PDT 2025
https://github.com/cor3ntin updated https://github.com/llvm/llvm-project/pull/139693
>From 79bb502c9ca1e35fb76b71b528cc7a12940ce1d8 Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Tue, 13 May 2025 11:00:51 +0200
Subject: [PATCH] [Clang] Remove workaround for libstdc++4.7
We document libstdc++4.8 as the minimum supported version,
and we carried a hack for `include/tr1/hashtable.h` fixed in 4.7.
Cleanup some libstdc++ compatibility comments.
---
clang/docs/ReleaseNotes.rst | 2 +
clang/lib/Parse/ParseDecl.cpp | 7 ++--
clang/lib/Sema/SemaInit.cpp | 38 +++++--------------
clang/test/SemaCXX/libstdcxx_gets_hack.cpp | 28 --------------
.../libstdcxx_pointer_return_false_hack.cpp | 34 -----------------
5 files changed, 15 insertions(+), 94 deletions(-)
delete mode 100644 clang/test/SemaCXX/libstdcxx_gets_hack.cpp
delete mode 100644 clang/test/SemaCXX/libstdcxx_pointer_return_false_hack.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index fb0318146aa60..6dc911c220603 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -58,6 +58,8 @@ C++ Specific Potentially Breaking Changes
- The type trait builtin ``__is_referenceable`` has been removed, since it has
very few users and all the type traits that could benefit from it in the
standard library already have their own bespoke builtins.
+- A workaround for libstdc++4.7 has been removed. Note that 4.8.3 remains the oldest
+ supported libstdc++ version.
ABI Changes in This Version
---------------------------
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 4fe3565687905..02b3a14134873 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -4024,13 +4024,14 @@ void Parser::ParseDeclarationSpecifiers(
}
case tok::kw___is_signed:
- // GNU libstdc++ 4.4 uses __is_signed as an identifier, but Clang
- // typically treats it as a trait. If we see __is_signed as it appears
- // in libstdc++, e.g.,
+ // HACK: before 2022-12, libstdc++ uses __is_signed as an identifier,
+ // but Clang typically treats it as a trait.
+ // If we see __is_signed as it appears in libstdc++, e.g.,
//
// static const bool __is_signed;
//
// then treat __is_signed as an identifier rather than as a keyword.
+ // This was fixed by libstdc++ in December 2022.
if (DS.getTypeSpecType() == TST_bool &&
DS.getTypeQualifiers() == DeclSpec::TQ_const &&
DS.getStorageClassSpec() == DeclSpec::SCS_static)
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index e5670dab03cb0..dc12bacc0158b 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -637,11 +637,11 @@ ExprResult InitListChecker::PerformEmptyInit(SourceLocation Loc,
}
InitializationSequence InitSeq(SemaRef, Entity, Kind, SubInit);
- // libstdc++4.6 marks the vector default constructor as explicit in
- // _GLIBCXX_DEBUG mode, so recover using the C++03 logic in that case.
- // stlport does so too. Look for std::__debug for libstdc++, and for
- // std:: for stlport. This is effectively a compiler-side implementation of
- // LWG2193.
+ // HACK: libstdc++ prior to 4.9 marks the vector default constructor
+ // as explicit in _GLIBCXX_DEBUG mode, so recover using the C++03 logic
+ // in that case. stlport does so too.
+ // Look for std::__debug for libstdc++, and for std:: for stlport.
+ // This is effectively a compiler-side implementation of LWG2193.
if (!InitSeq && EmptyInitList && InitSeq.getFailureKind() ==
InitializationSequence::FK_ExplicitConstructor) {
OverloadCandidateSet::iterator Best;
@@ -6240,24 +6240,6 @@ static void TryUserDefinedConversion(Sema &S,
}
}
-/// An egregious hack for compatibility with libstdc++-4.2: in <tr1/hashtable>,
-/// a function with a pointer return type contains a 'return false;' statement.
-/// In C++11, 'false' is not a null pointer, so this breaks the build of any
-/// code using that header.
-///
-/// Work around this by treating 'return false;' as zero-initializing the result
-/// if it's used in a pointer-returning function in a system header.
-static bool isLibstdcxxPointerReturnFalseHack(Sema &S,
- const InitializedEntity &Entity,
- const Expr *Init) {
- return S.getLangOpts().CPlusPlus11 &&
- Entity.getKind() == InitializedEntity::EK_Result &&
- Entity.getType()->isPointerType() &&
- isa<CXXBoolLiteralExpr>(Init) &&
- !cast<CXXBoolLiteralExpr>(Init)->getValue() &&
- S.getSourceManager().isInSystemHeader(Init->getExprLoc());
-}
-
/// The non-zero enum values here are indexes into diagnostic alternatives.
enum InvalidICRKind { IIK_okay, IIK_nonlocal, IIK_nonscalar };
@@ -6943,12 +6925,10 @@ void InitializationSequence::InitializeFrom(Sema &S,
AddPassByIndirectCopyRestoreStep(DestType, ShouldCopy);
} else if (ICS.isBad()) {
- if (isLibstdcxxPointerReturnFalseHack(S, Entity, Initializer))
- AddZeroInitializationStep(Entity.getType());
- else if (DeclAccessPair Found;
- Initializer->getType() == Context.OverloadTy &&
- !S.ResolveAddressOfOverloadedFunction(Initializer, DestType,
- /*Complain=*/false, Found))
+ if (DeclAccessPair Found;
+ Initializer->getType() == Context.OverloadTy &&
+ !S.ResolveAddressOfOverloadedFunction(Initializer, DestType,
+ /*Complain=*/false, Found))
SetFailed(InitializationSequence::FK_AddressOfOverloadFailed);
else if (Initializer->getType()->isFunctionType() &&
isExprAnUnaddressableFunction(S, Initializer))
diff --git a/clang/test/SemaCXX/libstdcxx_gets_hack.cpp b/clang/test/SemaCXX/libstdcxx_gets_hack.cpp
deleted file mode 100644
index 0d915d01474c3..0000000000000
--- a/clang/test/SemaCXX/libstdcxx_gets_hack.cpp
+++ /dev/null
@@ -1,28 +0,0 @@
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++14 -verify
-
-// This is a test for an egregious hack in Clang that works around
-// an issue with libstdc++'s detection of whether glibc provides a
-// ::gets function. If there is no ::gets, ignore
-// using ::gets;
-// in namespace std.
-//
-// See PR18402 and gcc.gnu.org/PR77795 for more details.
-
-#ifdef BE_THE_HEADER
-
-#pragma GCC system_header
-namespace std {
- using ::gets;
- using ::getx; // expected-error {{no member named 'getx'}}
-}
-
-#else
-
-#define BE_THE_HEADER
-#include "libstdcxx_pointer_return_false_hack.cpp"
-
-namespace foo {
- using ::gets; // expected-error {{no member named 'gets'}}
-}
-
-#endif
diff --git a/clang/test/SemaCXX/libstdcxx_pointer_return_false_hack.cpp b/clang/test/SemaCXX/libstdcxx_pointer_return_false_hack.cpp
deleted file mode 100644
index 17e1548ac50d6..0000000000000
--- a/clang/test/SemaCXX/libstdcxx_pointer_return_false_hack.cpp
+++ /dev/null
@@ -1,34 +0,0 @@
-// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify
-
-// This is a test for an egregious hack in Clang that works around
-// an issue with libstdc++-4.2's <tr1/hashtable> implementation.
-// The code in question returns 'false' from a function with a pointer
-// return type, which is ill-formed in C++11.
-
-#ifdef BE_THE_HEADER
-
-#pragma GCC system_header
-namespace std {
- namespace tr1 {
- template<typename T> struct hashnode;
- template<typename T> struct hashtable {
- typedef hashnode<T> node;
- node *find_node() {
- // This is ill-formed in C++11, per core issue 903, but we accept
- // it anyway in a system header.
- return false;
- }
- };
- }
-}
-
-#else
-
-#define BE_THE_HEADER
-#include "libstdcxx_pointer_return_false_hack.cpp"
-
-auto *test1 = std::tr1::hashtable<int>().find_node();
-
-void *test2() { return false; } // expected-error {{cannot initialize}}
-
-#endif
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