[clang++] Assertion `isa<IncompleteArrayType>(AT) && "Expected incomplete array"' failed.

[yijan4845]

This testcase is generated by a fuzzer.

Compiler Explorer: https://godbolt.org/z/a5Y7138jx

This invalid code will crash on Clang Trunk and Clang Assertion Trunk:

int F();
int b(int(&&)[F()]); 

void f() {
  b({1});
}

It seems that this goes back to clang-6.

Stack dump:

clang++: /root/llvm-project/clang/lib/Sema/SemaOverload.cpp:5520: clang::ImplicitConversionSequence TryListConversion(clang::Sema&, clang::InitListExpr*, clang::QualType, bool, bool, bool): Assertion `isa<IncompleteArrayType>(AT) && "Expected incomplete array"' 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 -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -O3 <source>
1.	<source>:5:8: current parser token ')'
2.	<source>:4:10: parsing function body 'f'
3.	<source>:4:10: in compound statement ('{}')
 #0 0x0000000003bba5a8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bba5a8)
 #1 0x0000000003bb826c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bb826c)
 #2 0x0000000003b05858 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x000078fd28842520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x000078fd288969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x000078fd28842476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x000078fd288287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x000078fd2882871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x000078fd28839e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x000000000710295f TryListConversion(clang::Sema&, clang::InitListExpr*, clang::QualType, bool, bool, bool) SemaOverload.cpp:0:0
#10 0x0000000007101bfb TryListConversion(clang::Sema&, clang::InitListExpr*, clang::QualType, bool, bool, bool) SemaOverload.cpp:0:0
#11 0x00000000071029c6 TryCopyInitialization(clang::Sema&, clang::Expr*, clang::QualType, bool, bool, bool, bool) SemaOverload.cpp:0:0
#12 0x00000000071054f0 clang::Sema::AddOverloadCandidate(clang::FunctionDecl*, clang::DeclAccessPair, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, bool, bool, bool, clang::CallExpr::ADLCallKind, llvm::MutableArrayRef<clang::ImplicitConversionSequence>, clang::OverloadCandidateParamOrder, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71054f0)
#13 0x000000000710f4e8 AddOverloadedCallCandidate(clang::Sema&, clang::DeclAccessPair, clang::TemplateArgumentListInfo*, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, bool) SemaOverload.cpp:0:0
#14 0x000000000710f809 clang::Sema::AddOverloadedCallCandidates(clang::UnresolvedLookupExpr*, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x710f809)
#15 0x000000000710fb0e clang::Sema::buildOverloadedCallSet(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::OverloadCandidateSet*, clang::ActionResult<clang::Expr*, true>*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x710fb0e)
#16 0x000000000711c205 clang::Sema::BuildOverloadedCallExpr(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x711c205)
#17 0x0000000006c8d5b8 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c8d5b8)
#18 0x0000000006c8fb1c clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c8fb1c)
#19 0x00000000066fb2fd clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult<clang::Expr*, true>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66fb2fd)
#20 0x00000000066f3cc1 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f3cc1)
#21 0x00000000066f5e17 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f5e17)
#22 0x00000000066f5ea9 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f5ea9)
#23 0x00000000066fa8c9 clang::Parser::ParseExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66fa8c9)
#24 0x000000000677d6d9 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x677d6d9)
#25 0x0000000006773a4c 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+++0x6773a4c)
#26 0x0000000006774960 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6774960)
#27 0x0000000006775835 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6775835)
#28 0x0000000006776f8a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6776f8a)
#29 0x000000000668ab13 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x668ab13)
#30 0x00000000066bf1cd clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66bf1cd)
#31 0x000000000667e85e clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x667e85e)
#32 0x000000000667f01e clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x667f01e)
#33 0x00000000066867b3 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66867b3)
#34 0x000000000668769d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x668769d)
#35 0x0000000006679bba clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6679bba)
#36 0x0000000004530518 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4530518)
#37 0x00000000047eb7d9 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47eb7d9)
#38 0x000000000476a2ce clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x476a2ce)
#39 0x00000000048d0eae clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48d0eae)
#40 0x0000000000cde2ef cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcde2ef)
#41 0x0000000000cd5ffa ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#42 0x0000000004574239 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
#43 0x0000000003b05d04 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b05d04)
#44 0x000000000457482f 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
#45 0x000000000453a12d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x453a12d)
#46 0x000000000453b21d 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+++0x453b21d)
#47 0x0000000004542b45 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4542b45)
#48 0x0000000000cdb1bf clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdb1bf)
#49 0x0000000000baa2b4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbaa2b4)
#50 0x000078fd28829d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#51 0x000078fd28829e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#52 0x0000000000cd5aae _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcd5aae)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Yihan Yang (yijan4845)

**This testcase is generated by a fuzzer.**

Compiler Explorer: https://godbolt.org/z/a5Y7138jx

This invalid code will crash on Clang Trunk and Clang Assertion Trunk:

int F();
int b(int(&&)[F()]); 

void f() {
  b({1});
}

It seems that this goes back to clang-6.

Stack dump:

clang++: /root/llvm-project/clang/lib/Sema/SemaOverload.cpp:5520: clang::ImplicitConversionSequence TryListConversion(clang::Sema&, clang::InitListExpr*, clang::QualType, bool, bool, bool): Assertion `isa<IncompleteArrayType>(AT) && "Expected incomplete array"' 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 -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -O3 <source>
1.	<source>:5:8: current parser token ')'
2.	<source>:4:10: parsing function body 'f'
3.	<source>:4:10: in compound statement ('{}')
 #<!-- -->0 0x0000000003bba5a8 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bba5a8)
 #<!-- -->1 0x0000000003bb826c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bb826c)
 #<!-- -->2 0x0000000003b05858 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x000078fd28842520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #<!-- -->4 0x000078fd288969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #<!-- -->5 0x000078fd28842476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #<!-- -->6 0x000078fd288287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #<!-- -->7 0x000078fd2882871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #<!-- -->8 0x000078fd28839e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #<!-- -->9 0x000000000710295f TryListConversion(clang::Sema&amp;, clang::InitListExpr*, clang::QualType, bool, bool, bool) SemaOverload.cpp:0:0
#<!-- -->10 0x0000000007101bfb TryListConversion(clang::Sema&amp;, clang::InitListExpr*, clang::QualType, bool, bool, bool) SemaOverload.cpp:0:0
#<!-- -->11 0x00000000071029c6 TryCopyInitialization(clang::Sema&amp;, clang::Expr*, clang::QualType, bool, bool, bool, bool) SemaOverload.cpp:0:0
#<!-- -->12 0x00000000071054f0 clang::Sema::AddOverloadCandidate(clang::FunctionDecl*, clang::DeclAccessPair, llvm::ArrayRef&lt;clang::Expr*&gt;, clang::OverloadCandidateSet&amp;, bool, bool, bool, bool, clang::CallExpr::ADLCallKind, llvm::MutableArrayRef&lt;clang::ImplicitConversionSequence&gt;, clang::OverloadCandidateParamOrder, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71054f0)
#<!-- -->13 0x000000000710f4e8 AddOverloadedCallCandidate(clang::Sema&amp;, clang::DeclAccessPair, clang::TemplateArgumentListInfo*, llvm::ArrayRef&lt;clang::Expr*&gt;, clang::OverloadCandidateSet&amp;, bool, bool) SemaOverload.cpp:0:0
#<!-- -->14 0x000000000710f809 clang::Sema::AddOverloadedCallCandidates(clang::UnresolvedLookupExpr*, llvm::ArrayRef&lt;clang::Expr*&gt;, clang::OverloadCandidateSet&amp;, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x710f809)
#<!-- -->15 0x000000000710fb0e clang::Sema::buildOverloadedCallSet(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::OverloadCandidateSet*, clang::ActionResult&lt;clang::Expr*, true&gt;*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x710fb0e)
#<!-- -->16 0x000000000711c205 clang::Sema::BuildOverloadedCallExpr(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x711c205)
#<!-- -->17 0x0000000006c8d5b8 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c8d5b8)
#<!-- -->18 0x0000000006c8fb1c clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c8fb1c)
#<!-- -->19 0x00000000066fb2fd clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult&lt;clang::Expr*, true&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66fb2fd)
#<!-- -->20 0x00000000066f3cc1 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&amp;, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f3cc1)
#<!-- -->21 0x00000000066f5e17 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f5e17)
#<!-- -->22 0x00000000066f5ea9 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f5ea9)
#<!-- -->23 0x00000000066fa8c9 clang::Parser::ParseExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66fa8c9)
#<!-- -->24 0x000000000677d6d9 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x677d6d9)
#<!-- -->25 0x0000000006773a4c 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+++0x6773a4c)
#<!-- -->26 0x0000000006774960 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector&lt;clang::Stmt*, 32u&gt;&amp;, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6774960)
#<!-- -->27 0x0000000006775835 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6775835)
#<!-- -->28 0x0000000006776f8a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6776f8a)
#<!-- -->29 0x000000000668ab13 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x668ab13)
#<!-- -->30 0x00000000066bf1cd clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&amp;, clang::DeclaratorContext, clang::ParsedAttributes&amp;, clang::Parser::ParsedTemplateInfo&amp;, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66bf1cd)
#<!-- -->31 0x000000000667e85e clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec&amp;, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x667e85e)
#<!-- -->32 0x000000000667f01e clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x667f01e)
#<!-- -->33 0x00000000066867b3 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66867b3)
#<!-- -->34 0x000000000668769d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x668769d)
#<!-- -->35 0x0000000006679bba clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6679bba)
#<!-- -->36 0x0000000004530518 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4530518)
#<!-- -->37 0x00000000047eb7d9 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47eb7d9)
#<!-- -->38 0x000000000476a2ce clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x476a2ce)
#<!-- -->39 0x00000000048d0eae clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48d0eae)
#<!-- -->40 0x0000000000cde2ef cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcde2ef)
#<!-- -->41 0x0000000000cd5ffa ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->42 0x0000000004574239 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
#<!-- -->43 0x0000000003b05d04 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b05d04)
#<!-- -->44 0x000000000457482f 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
#<!-- -->45 0x000000000453a12d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x453a12d)
#<!-- -->46 0x000000000453b21d 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+++0x453b21d)
#<!-- -->47 0x0000000004542b45 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+++0x4542b45)
#<!-- -->48 0x0000000000cdb1bf clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdb1bf)
#<!-- -->49 0x0000000000baa2b4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbaa2b4)
#<!-- -->50 0x000078fd28829d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#<!-- -->51 0x000078fd28829e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#<!-- -->52 0x0000000000cd5aae _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcd5aae)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[shafik]

So we are treating [F()] as a variable length array which I don't believe should be well-formed, gcc rejects this: https://godbolt.org/z/fY1aMsoj5

<source>:2:15: warning: variable length arrays in C++ are a Clang extension [-Wvla-cxx-extension]
    2 | int b(int(&&)[F()]); 
      |               ^~~

So believe we should be diagnosing this and that would probably prevent the crash.

CC @AaronBallman @Fznamznon ... more VLA fun

[AaronBallman]

It is forming a VLA, so we should diagnose the extension and accept the code. I'm not certain why GCC is rejecting that, it's a valid declaration of an rvalue reference to a VLA, if you support VLAs (which both GCC and Clang do in C++ mode).