[clang] Crash from constexpr-evaluation of structured-binding variable

[hazohelet]

The use of &c at the end of the following code causes clang ICE.

using size_t = decltype(sizeof(0));

namespace std {
template <typename T> struct tuple_size;
template <size_t, typename> struct tuple_element;
} // namespace std

template <typename T> struct std::tuple_size<const T> : std::tuple_size<T> {};
template <size_t N, typename T> struct std::tuple_element<N, const T> {
  typedef const typename std::tuple_element<N, T>::type type;
};

struct C {
  template <int> int get() const;
};
template <> struct std::tuple_size<C> {
  static const int value = 1;
};
template <> struct std::tuple_element<0, C> {
  typedef int type;
};

template <const C *p> void f() {
  const auto &[c] = *p;
  &c;
}

Live demo: https://godbolt.org/z/918oE41Ke
Backtrace:

clang++: /root/llvm-project/clang/lib/AST/ExprConstant.cpp:3381: bool evaluateVarDeclInit({anonymous}::EvalInfo&, const clang::Expr*, const clang::VarDecl*, {anonymous}::CallStackFrame*, unsigned int, clang::APValue*&):
Assertion `!VD->mightBeUsableInConstantExpressions(Info.Ctx)' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
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 -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++2b <source>
1.	<source>:25:5: current parser token ';'
2.	<source>:23:32: parsing function body 'f'
3.	<source>:23:32: in compound statement ('{}')
 #0 0x0000000003708fb8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3708fb8)
 #1 0x0000000003706c7c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3706c7c)
 #2 0x000000000364f8d8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f76867d4420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00007f768629700b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #5 0x00007f7686276859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #6 0x00007f7686276729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #7 0x00007f7686287fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #8 0x0000000006f80225 (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f80225)
 #9 0x0000000006fa9b66 (anonymous namespace)::LValueExprEvaluator::VisitVarDecl(clang::Expr const*, clang::VarDecl const*) ExprConstant.cpp:0:0
#10 0x0000000006fe7e9b (anonymous namespace)::LValueExprEvaluator::VisitDeclRefExpr(clang::DeclRefExpr const*) ExprConstant.cpp:0:0
#11 0x0000000006fc4837 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::LValueExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#12 0x0000000006fe7eb6 (anonymous namespace)::LValueExprEvaluator::VisitDeclRefExpr(clang::DeclRefExpr const*) ExprConstant.cpp:0:0
#13 0x0000000006fc4837 clang::StmtVisitorBase<llvm::make_const_ptr, (anonymous namespace)::LValueExprEvaluator, bool>::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#14 0x0000000006fc5d8d EvaluateLValue(clang::Expr const*, (anonymous namespace)::LValue&, (anonymous namespace)::EvalInfo&, bool) ExprConstant.cpp:0:0
#15 0x0000000006f9a14e Evaluate(clang::APValue&, (anonymous namespace)::EvalInfo&, clang::Expr const*) ExprConstant.cpp:0:0
#16 0x0000000006fb8e42 EvaluateInPlace(clang::APValue&, (anonymous namespace)::EvalInfo&, (anonymous namespace)::LValue const&, clang::Expr const*, bool) ExprConstant.cpp:0:0
#17 0x0000000006ff4208 clang::Expr::EvaluateAsConstantExpr(clang::Expr::EvalResult&, clang::ASTContext const&, clang::Expr::ConstantExprKind) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ff4208)
#18 0x0000000006eaf122 clang::computeDependence(clang::UnaryOperator*, clang::ASTContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6eaf122)
#19 0x0000000006f623f3 clang::UnaryOperator::Create(clang::ASTContext const&, clang::Expr*, clang::UnaryOperatorKind, clang::QualType, clang::ExprValueKind, clang::ExprObjectKind, clang::SourceLocation, bool, clang::FPOptionsOverride) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f623f3)
#20 0x00000000063ffa0f clang::Sema::CreateBuiltinUnaryOp(clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63ffa0f)
#21 0x00000000064004ed clang::Sema::BuildUnaryOp(clang::Scope*, clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64004ed)
#22 0x0000000005ed5bf9 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ed5bf9)
#23 0x0000000005ed7d8a clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ed7d8a)
#24 0x0000000005ed7f29 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ed7f29)
#25 0x0000000005edcc29 clang::Parser::ParseExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5edcc29)
#26 0x0000000005f57dc7 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f57dc7)
#27 0x0000000005f4e43d clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f4e43d)
#28 0x0000000005f4f278 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f4f278)
#29 0x0000000005f501b9 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f501b9)
#30 0x0000000005f51ada clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f51ada)
#31 0x0000000005e7f1c1 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e7f1c1)
#32 0x0000000005f6b520 clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f6b520)
#33 0x0000000005f70a18 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#34 0x0000000005f70cd3 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f70cd3)
#35 0x0000000005eaea0b clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5eaea0b)
#36 0x0000000005e79814 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e79814)
#37 0x0000000005e7a71d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e7a71d)
#38 0x0000000005e6ea5a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6ea5a)
#39 0x00000000049724d8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49724d8)
#40 0x00000000041d6509 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41d6509)
#41 0x00000000041571ee clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41571ee)
#42 0x00000000042b584e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42b584e)
#43 0x0000000000bdcb46 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbdcb46)
#44 0x0000000000bd440a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#45 0x0000000003fb4a69 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
#46 0x000000000364fd84 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x364fd84)
#47 0x0000000003fb505f 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
#48 0x0000000003f7d3a5 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f7d3a5)
#49 0x0000000003f7de0d 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+++0x3f7de0d)
#50 0x0000000003f85d35 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f85d35)
#51 0x0000000000bd9fec clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd9fec)
#52 0x0000000000ad4d61 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xad4d61)
#53 0x00007f7686278083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#54 0x0000000000bd3eee _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd3eee)

[llvmbot]

@llvm/issue-subscribers-clang-frontend

The use of `&c` at the end of the following code causes clang ICE.

using size_t = decltype(sizeof(0));

namespace std {
template <typename T> struct tuple_size;
template <size_t, typename> struct tuple_element;
} // namespace std

template <typename T> struct std::tuple_size<const T> : std::tuple_size<T> {};
template <size_t N, typename T> struct std::tuple_element<N, const T> {
  typedef const typename std::tuple_element<N, T>::type type;
};

struct C {
  template <int> int get() const;
};
template <> struct std::tuple_size<C> {
  static const int value = 1;
};
template <> struct std::tuple_element<0, C> {
  typedef int type;
};

template <const C *p> void f() {
  const auto &[c] = *p;
  &c;
}

Live demo: https://godbolt.org/z/918oE41Ke
Backtrace:

clang++: /root/llvm-project/clang/lib/AST/ExprConstant.cpp:3381: bool evaluateVarDeclInit({anonymous}::EvalInfo&, const clang::Expr*, const clang::VarDecl*, {anonymous}::CallStackFrame*, unsigned int, clang::APValue*&):
Assertion `!VD->mightBeUsableInConstantExpressions(Info.Ctx)' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
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 -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++2b <source>
1.	<source>:25:5: current parser token ';'
2.	<source>:23:32: parsing function body 'f'
3.	<source>:23:32: in compound statement ('{}')
 #<!-- -->0 0x0000000003708fb8 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3708fb8)
 #<!-- -->1 0x0000000003706c7c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3706c7c)
 #<!-- -->2 0x000000000364f8d8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007f76867d4420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #<!-- -->4 0x00007f768629700b raise (/lib/x86_64-linux-gnu/libc.so.6+0x4300b)
 #<!-- -->5 0x00007f7686276859 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22859)
 #<!-- -->6 0x00007f7686276729 (/lib/x86_64-linux-gnu/libc.so.6+0x22729)
 #<!-- -->7 0x00007f7686287fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
 #<!-- -->8 0x0000000006f80225 (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f80225)
 #<!-- -->9 0x0000000006fa9b66 (anonymous namespace)::LValueExprEvaluator::VisitVarDecl(clang::Expr const*, clang::VarDecl const*) ExprConstant.cpp:0:0
#<!-- -->10 0x0000000006fe7e9b (anonymous namespace)::LValueExprEvaluator::VisitDeclRefExpr(clang::DeclRefExpr const*) ExprConstant.cpp:0:0
#<!-- -->11 0x0000000006fc4837 clang::StmtVisitorBase&lt;llvm::make_const_ptr, (anonymous namespace)::LValueExprEvaluator, bool&gt;::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#<!-- -->12 0x0000000006fe7eb6 (anonymous namespace)::LValueExprEvaluator::VisitDeclRefExpr(clang::DeclRefExpr const*) ExprConstant.cpp:0:0
#<!-- -->13 0x0000000006fc4837 clang::StmtVisitorBase&lt;llvm::make_const_ptr, (anonymous namespace)::LValueExprEvaluator, bool&gt;::Visit(clang::Stmt const*) ExprConstant.cpp:0:0
#<!-- -->14 0x0000000006fc5d8d EvaluateLValue(clang::Expr const*, (anonymous namespace)::LValue&amp;, (anonymous namespace)::EvalInfo&amp;, bool) ExprConstant.cpp:0:0
#<!-- -->15 0x0000000006f9a14e Evaluate(clang::APValue&amp;, (anonymous namespace)::EvalInfo&amp;, clang::Expr const*) ExprConstant.cpp:0:0
#<!-- -->16 0x0000000006fb8e42 EvaluateInPlace(clang::APValue&amp;, (anonymous namespace)::EvalInfo&amp;, (anonymous namespace)::LValue const&amp;, clang::Expr const*, bool) ExprConstant.cpp:0:0
#<!-- -->17 0x0000000006ff4208 clang::Expr::EvaluateAsConstantExpr(clang::Expr::EvalResult&amp;, clang::ASTContext const&amp;, clang::Expr::ConstantExprKind) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ff4208)
#<!-- -->18 0x0000000006eaf122 clang::computeDependence(clang::UnaryOperator*, clang::ASTContext const&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6eaf122)
#<!-- -->19 0x0000000006f623f3 clang::UnaryOperator::Create(clang::ASTContext const&amp;, clang::Expr*, clang::UnaryOperatorKind, clang::QualType, clang::ExprValueKind, clang::ExprObjectKind, clang::SourceLocation, bool, clang::FPOptionsOverride) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f623f3)
#<!-- -->20 0x00000000063ffa0f clang::Sema::CreateBuiltinUnaryOp(clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63ffa0f)
#<!-- -->21 0x00000000064004ed clang::Sema::BuildUnaryOp(clang::Scope*, clang::SourceLocation, clang::UnaryOperatorKind, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x64004ed)
#<!-- -->22 0x0000000005ed5bf9 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&amp;, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ed5bf9)
#<!-- -->23 0x0000000005ed7d8a clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ed7d8a)
#<!-- -->24 0x0000000005ed7f29 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ed7f29)
#<!-- -->25 0x0000000005edcc29 clang::Parser::ParseExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5edcc29)
#<!-- -->26 0x0000000005f57dc7 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f57dc7)
#<!-- -->27 0x0000000005f4e43d clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector&lt;clang::Stmt*, 32u&gt;&amp;, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f4e43d)
#<!-- -->28 0x0000000005f4f278 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector&lt;clang::Stmt*, 32u&gt;&amp;, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f4f278)
#<!-- -->29 0x0000000005f501b9 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f501b9)
#<!-- -->30 0x0000000005f51ada clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f51ada)
#<!-- -->31 0x0000000005e7f1c1 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e7f1c1)
#<!-- -->32 0x0000000005f6b520 clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&amp;, clang::ParsingDeclRAIIObject&amp;, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f6b520)
#<!-- -->33 0x0000000005f70a18 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#<!-- -->34 0x0000000005f70cd3 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5f70cd3)
#<!-- -->35 0x0000000005eaea0b clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5eaea0b)
#<!-- -->36 0x0000000005e79814 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e79814)
#<!-- -->37 0x0000000005e7a71d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e7a71d)
#<!-- -->38 0x0000000005e6ea5a clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6ea5a)
#<!-- -->39 0x00000000049724d8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49724d8)
#<!-- -->40 0x00000000041d6509 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41d6509)
#<!-- -->41 0x00000000041571ee clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41571ee)
#<!-- -->42 0x00000000042b584e clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42b584e)
#<!-- -->43 0x0000000000bdcb46 cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbdcb46)
#<!-- -->44 0x0000000000bd440a ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->45 0x0000000003fb4a69 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
#<!-- -->46 0x000000000364fd84 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x364fd84)
#<!-- -->47 0x0000000003fb505f 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
#<!-- -->48 0x0000000003f7d3a5 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f7d3a5)
#<!-- -->49 0x0000000003f7de0d 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+++0x3f7de0d)
#<!-- -->50 0x0000000003f85d35 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+++0x3f85d35)
#<!-- -->51 0x0000000000bd9fec clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd9fec)
#<!-- -->52 0x0000000000ad4d61 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xad4d61)
#<!-- -->53 0x00007f7686278083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#<!-- -->54 0x0000000000bd3eee _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd3eee)

[shafik]

Looks like it started in clang12: https://godbolt.org/z/n9z9P1fca

Looks related to but not identical to: #53598

[shafik]

I reduced it to this: https://godbolt.org/z/3c5rzxorT

struct C {
  int x;
};

template <const C *p> void f() {
  const auto &[c] = *p;
  &c;
}

and then the backtrace looks like: #53598

so I think these are probably the same problem but different ways of hitting it but not 💯

[tbaederr]

llvm-project/clang/lib/AST/ExprConstant.cpp

Lines 3375 to 3390 in 4b4d383

	if (Init->isValueDependent()) {
	// The DeclRefExpr is not value-dependent, but the variable it refers to
	// has a value-dependent initializer. This should only happen in
	// constant-folding cases, where the variable is not actually of a suitable
	// type for use in a constant expression (otherwise the DeclRefExpr would
	// have been value-dependent too), so diagnose that.
	assert(!VD->mightBeUsableInConstantExpressions(Info.Ctx));
	if (!Info.checkingPotentialConstantExpression()) {
	Info.FFDiag(E, Info.getLangOpts().CPlusPlus11
	? diag::note_constexpr_ltor_non_constexpr
	: diag::note_constexpr_ltor_non_integral, 1)
	<< VD << VD->getType();
	NoteLValueLocation(Info, Base);
	}
	return false;
	}

The comment here says "The DeclRefExpr is not value-dependent" - but it is:

(lldb) p Init->isValueDependent()
(bool) $0 = true
(lldb) p E->isValueDependent()
(bool) $1 = true
(lldb)

[tbaederr]

So, this fixes the reproducer:

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 04a751f1b4d0..a3a9ccdab523 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -3306,6 +3306,8 @@ static bool HandleLValueComplexElement(EvalInfo &Info, const Expr *E,
 static bool evaluateVarDeclInit(EvalInfo &Info, const Expr *E,
                                 const VarDecl *VD, CallStackFrame *Frame,
                                 unsigned Version, APValue *&Result) {
+  if (E->isValueDependent())
+    return false;
   APValue::LValueBase Base(VD, Frame ? Frame->Index : 0, Version);

   // If this is a local variable, dig out its value.

[shafik]

How do we end up in HandleLValueComplexElement(...)?

[tbaederr]

we aren't, this is in evaluateVarDeclInit

[cor3ntin]

@tbaederr are you going to submit a patch?