Skip to content

Clang Crash When Defining operator<< as a Friend Template Function of a Class Template since clang 20 #139052

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom
Closed
mariete1223 opened this issue May 8, 2025 · 2 comments · Fixed by #139436
Closed

Clang Crash When Defining operator<< as a Friend Template Function of a Class Template since clang 20 #139052

mariete1223 opened this issue May 8, 2025 · 2 comments · Fixed by #139436
Labels
clang:frontend Language frontend issues, e.g. anything involving "Sema" confirmed Verified by a second party crash-on-invalid regression:20 Regression in 20 release

Comments

@mariete1223
Copy link

Clang crashes during instantiation of a friend function template declared outside the class when used with BinaryTree. The crash occurs in the function InstantiateFunctionDefinition in clang 20. Haven´t been able to reduce code more

Assertion

clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:5767: void clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool): Assertion `It != Primary->redecls().end() && "Should't get here without a definition"' failed.`

Stack dump

Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -x c++ <source>
1.	<eof> parser at end of file
2.	<source>:19:26: instantiating function definition 'operator<<<int>'
 #0 0x0000000003f7c0a8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f7c0a8)
 #1 0x0000000003f79d34 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f79d34)
 #2 0x0000000003ebebf8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x0000790a8e642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x0000790a8e6969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x0000790a8e642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x0000790a8e6287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000790a8e62871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x0000790a8e639e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x0000000007244186 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7244186)
#10 0x0000000007241b46 clang::Sema::PerformPendingInstantiations(bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7241b46)
#11 0x0000000006790242 clang::Sema::ActOnEndOfTranslationUnitFragment(clang::TUFragmentKind) (.part.0) Sema.cpp:0:0
#12 0x0000000006790ae2 clang::Sema::ActOnEndOfTranslationUnit() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6790ae2)
#13 0x00000000065fe6eb clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65fe6eb)
#14 0x00000000065f09ea clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65f09ea)
#15 0x000000000491ebe8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x491ebe8)
#16 0x0000000004c11f15 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c11f15)
#17 0x0000000004b9131e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b9131e)
#18 0x0000000004d05d39 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4d05d39)
#19 0x0000000000da788f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda788f)
#20 0x0000000000d9da5a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#21 0x00000000049854a9 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#22 0x0000000003ebf094 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ebf094)
#23 0x0000000004985abf clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#24 0x0000000004947f0d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4947f0d)
#25 0x0000000004948f9e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4948f9e)
#26 0x0000000004950df5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4950df5)
#27 0x0000000000da37f8 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda37f8)
#28 0x0000000000c28b74 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc28b74)
#29 0x0000790a8e629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#30 0x0000790a8e629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#31 0x0000000000d9d505 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9d505)

Program

#include <iostream>
#include <memory>
template <typename T>
class BinaryTree;
template <typename T>
std::ostream& operator<<(std::ostream& os, BinaryTree<T>& b);
template <typename T>
struct Node {
    Node(T data) : data(data) {}
    T data;
};
template <typename T>
struct BinaryTree {
    std::unique_ptr<Node<T>> root;
    BinaryTree() = default;
    BinaryTree(T data) {
        root = std::make_unique<Node<T>>(data);
    }
    friend std::ostream& operator<< <T>(std::ostream& os, BinaryTree& b) {
        return (b.root)? os << b.root->data : os << "<empty tree>";
    }
};
int main() {
    BinaryTree<int> a(1);
    std::cout << a << std::endl;
}

To quickly reproduce

it happens since clang 20

https://gcc.godbolt.org/z/WWWqdcbjj
@llvmbot llvmbot added the clang Clang issues not falling into any other category label May 8, 2025
@frederick-vs-ja
Copy link
Contributor

Reduced library-free example (Godbolt link):

struct FakeStream {};

template <typename T>
class BinaryTree;
template <typename T>
FakeStream& operator<<(FakeStream& os, BinaryTree<T>& b);

template <typename T>
struct BinaryTree {
  T* root{};
  friend FakeStream& operator<< <T>(FakeStream& os, BinaryTree&) {
    return os;
  }
};

int main() {
  FakeStream fakeout;
  BinaryTree<int> a{};
  fakeout << a;
}

@frederick-vs-ja frederick-vs-ja added clang:frontend Language frontend issues, e.g. anything involving "Sema" crash-on-invalid regression:20 Regression in 20 release and removed clang Clang issues not falling into any other category labels May 8, 2025
@llvmbot
Copy link
Member

llvmbot commented May 8, 2025

@llvm/issue-subscribers-clang-frontend

Author: None (mariete1223)

Clang crashes during instantiation of a friend function template declared outside the class when used with BinaryTree<T>. The crash occurs in the function InstantiateFunctionDefinition in clang 20. **Haven´t been able to reduce code more**

Assertion

clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:5767: void clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool): Assertion `It != Primary-&gt;redecls().end() &amp;&amp; "Should't get here without a definition"' failed.`

Stack dump

Stack dump:
0.	Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -x c++ &lt;source&gt;
1.	&lt;eof&gt; parser at end of file
2.	&lt;source&gt;:19:26: instantiating function definition 'operator&lt;&lt;&lt;int&gt;'
 #<!-- -->0 0x0000000003f7c0a8 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f7c0a8)
 #<!-- -->1 0x0000000003f79d34 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f79d34)
 #<!-- -->2 0x0000000003ebebf8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x0000790a8e642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #<!-- -->4 0x0000790a8e6969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #<!-- -->5 0x0000790a8e642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #<!-- -->6 0x0000790a8e6287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #<!-- -->7 0x0000790a8e62871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #<!-- -->8 0x0000790a8e639e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #<!-- -->9 0x0000000007244186 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7244186)
#<!-- -->10 0x0000000007241b46 clang::Sema::PerformPendingInstantiations(bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7241b46)
#<!-- -->11 0x0000000006790242 clang::Sema::ActOnEndOfTranslationUnitFragment(clang::TUFragmentKind) (.part.0) Sema.cpp:0:0
#<!-- -->12 0x0000000006790ae2 clang::Sema::ActOnEndOfTranslationUnit() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6790ae2)
#<!-- -->13 0x00000000065fe6eb clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65fe6eb)
#<!-- -->14 0x00000000065f09ea clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65f09ea)
#<!-- -->15 0x000000000491ebe8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x491ebe8)
#<!-- -->16 0x0000000004c11f15 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c11f15)
#<!-- -->17 0x0000000004b9131e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b9131e)
#<!-- -->18 0x0000000004d05d39 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4d05d39)
#<!-- -->19 0x0000000000da788f cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda788f)
#<!-- -->20 0x0000000000d9da5a ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->21 0x00000000049854a9 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::'lambda'()&gt;(long) Job.cpp:0:0
#<!-- -->22 0x0000000003ebf094 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ebf094)
#<!-- -->23 0x0000000004985abf clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (.part.0) Job.cpp:0:0
#<!-- -->24 0x0000000004947f0d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4947f0d)
#<!-- -->25 0x0000000004948f9e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4948f9e)
#<!-- -->26 0x0000000004950df5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4950df5)
#<!-- -->27 0x0000000000da37f8 clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda37f8)
#<!-- -->28 0x0000000000c28b74 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc28b74)
#<!-- -->29 0x0000790a8e629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#<!-- -->30 0x0000790a8e629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#<!-- -->31 0x0000000000d9d505 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9d505)

Program

#include &lt;iostream&gt;
#include &lt;memory&gt;
template &lt;typename T&gt;
class BinaryTree;
template &lt;typename T&gt;
std::ostream&amp; operator&lt;&lt;(std::ostream&amp; os, BinaryTree&lt;T&gt;&amp; b);
template &lt;typename T&gt;
struct Node {
    Node(T data) : data(data) {}
    T data;
};
template &lt;typename T&gt;
struct BinaryTree {
    std::unique_ptr&lt;Node&lt;T&gt;&gt; root;
    BinaryTree() = default;
    BinaryTree(T data) {
        root = std::make_unique&lt;Node&lt;T&gt;&gt;(data);
    }
    friend std::ostream&amp; operator&lt;&lt; &lt;T&gt;(std::ostream&amp; os, BinaryTree&amp; b) {
        return (b.root)? os &lt;&lt; b.root-&gt;data : os &lt;&lt; "&lt;empty tree&gt;";
    }
};
int main() {
    BinaryTree&lt;int&gt; a(1);
    std::cout &lt;&lt; a &lt;&lt; std::endl;
}

To quickly reproduce

it happens since clang 20

https://gcc.godbolt.org/z/WWWqdcbjj

@cor3ntin cor3ntin added the confirmed Verified by a second party label May 9, 2025
@zyn0217 zyn0217 mentioned this issue May 11, 2025
Merged
llvm-sync bot pushed a commit to arm/arm-toolchain that referenced this issue May 14, 2025
@zyn0217 @github-actions
Automerge: [Clang] Stop changing DC when instantiating dependent frie…
46f6c41 
…nd specializations (#139436)

Since 346077a, we began using the primary template's lexical
DeclContext for template arguments in order to properly instantiate a
friend definition.

There is a missed peculiar case, as in a friend template is specialized
within a dependent context. In this scenario, the primary template is
not a definition, whereas the specialization is. So the primary
template's DeclContext doesn't provide anything meaningful
for instantiation.

Fixes llvm/llvm-project#139052
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
clang:frontend Language frontend issues, e.g. anything involving "Sema" confirmed Verified by a second party crash-on-invalid regression:20 Regression in 20 release
Projects
None yet
Milestone
No milestone
Development

Successfully merging a pull request may close this issue.

[Clang] Stop changing DC when instantiating dependent friend specializations zyn0217/llvm-project
4 participants
@cor3ntin @frederick-vs-ja @llvmbot @mariete1223