clang++ segment fault in clang::Sema::ActOnCapScopeReturnStmt

[llvmbot]

Bugzilla Link	49183
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor,@fhahn,@zygoloid

Extended Description

The frontend fault blocks many downstream applications of clang (e.g., creduce).

Version 11.0.0 and 6.0.0 are affected.

int main() {
    auto a = [](void)__attribute__((b(({
    return 0;
}

$ cat /tmp/test-7c00f2.sh
# Crash reproducer for clang version 11.1.0 (https://github.com/llvm/llvm-project.git 1fdec59bffc11ae37eb51a1b9869f0696bfd5312)
# Driver args: "--driver-mode=g++" "test.cc"
# Original command:  "/data/xxx/git/llvm-project/build/bin/clang-11" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-emit-obj" "-mrelax-all" "-disable-free" "-main-file-name" "test.cc" "-mrelocation-model" "static" "-mframe-pointer=all" "-fmath-errno" "-fno-rounding-math" "-mconstructor-aliases" "-munwind-tables" "-target-cpu" "x86-64" "-fno-split-dwarf-inlining" "-debugger-tuning=gdb" "-resource-dir" "/data/xxx/git/llvm-project/build/lib/clang/11.1.0" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/x86_64-linux-gnu/c++/7.5.0" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/x86_64-linux-gnu/c++/7.5.0" "-internal-isystem" "/usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/backward" "-internal-isystem" "/usr/local/include" "-internal-isystem" "/data/xxx/git/llvm-project/build/lib/clang/11.1.0/include" "-internal-externc-isystem" "/usr/include/x86_64-linux-gnu" "-internal-externc-isystem" "/include" "-internal-externc-isystem" "/usr/include" "-fdeprecated-macro" "-fdebug-compilation-dir" "/data/xxx/docker_share/clang" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fcxx-exceptions" "-fexceptions" "-fcolor-diagnostics" "-faddrsig" "-o" "/tmp/test-f61719.o" "-x" "c++" "test.cc"
 "/data/xxx/git/llvm-project/build/bin/clang-11" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-emit-obj" "-mrelax-all" "-disable-free" "-main-file-name" "test.cc" "-mrelocation-model" "static" "-mframe-pointer=all" "-fmath-errno" "-fno-rounding-math" "-mconstructor-aliases" "-munwind-tables" "-target-cpu" "x86-64" "-fno-split-dwarf-inlining" "-debugger-tuning=gdb" "-fdeprecated-macro" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fcxx-exceptions" "-fexceptions" "-fcolor-diagnostics" "-faddrsig" "-x" "c++" "test-7c00f2.cpp"

$ ./clang++ test.cc
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: /data/xxx/git/llvm-project/build/bin/clang-11 -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all -disable-free -main-file-name test.cc -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -fno-split-dwarf-inlining -debugger-tuning=gdb -resource-dir /data/xxx/git/llvm-project/build/lib/clang/11.1.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/x86_64-linux-gnu/c++/7.5.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/x86_64-linux-gnu/c++/7.5.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/backward -internal-isystem /usr/local/include -internal-isystem /data/xxx/git/llvm-project/build/lib/clang/11.1.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /data/xxx/docker_share/clang -ferror-limit 19 -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -faddrsig -o /tmp/test-bc1970.o -x c++ test.cc
1.      test.cc:3:13: current parser token ';'
2.      test.cc:1:12: parsing function body 'main'
3.      test.cc:1:12: in compound statement ('{}')
4.      test.cc:2:14: lambda expression parsing
5.      test.cc:2:40: in compound statement ('{}')
 #​0 0x0000000006e97306 llvm::sys::PrintStackTrace(llvm::raw_ostream&) /home/xxx/data/git/llvm-project/llvm/lib/Support/Unix/Signals.inc:560:7
 #​1 0x0000000006e9266e llvm::sys::RunSignalHandlers() /home/xxx/data/git/llvm-project/llvm/lib/Support/Signals.cpp:69:18
 #​2 0x0000000006e97caa SignalHandler(int) /home/xxx/data/git/llvm-project/llvm/lib/Support/Unix/Signals.inc:396:3
 #​3 0x00007f0e755278a0 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x128a0)
 #&#8203;4 0x00000000075bcc95 llvm::PointerIntPair<void*, 1u, int, llvm::pointer_union_detail::PointerUnionUIntTraits<clang::TypeSourceInfo*, clang::DeclaratorDecl::ExtInfo*>, llvm::PointerIntPairInfo<void*, 1u, llvm::pointer_union_detail::PointerUnionUIntTraits<clang::TypeSourceInfo*, clang::DeclaratorDecl::ExtInfo*> > >::getInt() const /home/xxx/data/git/llvm-project/llvm/include/llvm/ADT/PointerIntPair.h:61:57
 #&#8203;5 0x00000000075bcc95 bool llvm::PointerUnion<clang::TypeSourceInfo*, clang::DeclaratorDecl::ExtInfo*>::is<clang::DeclaratorDecl::ExtInfo*>() const /home/xxx/data/git/llvm-project/llvm/include/llvm/ADT/PointerUnion.h:188:0
 #&#8203;6 0x00000000075bcc95 clang::DeclaratorDecl::hasExtInfo() const /home/xxx/data/git/llvm-project/clang/include/clang/AST/Decl.h:686:0
 #&#8203;7 0x00000000075bcc95 clang::DeclaratorDecl::getTypeSourceInfo() const /home/xxx/data/git/llvm-project/clang/include/clang/AST/Decl.h:701:0
 #&#8203;8 0x000000000df02e89 clang::TypeSourceInfo::getType() const /home/xxx/data/git/llvm-project/clang/include/clang/AST/Type.h:0:0
 #&#8203;9 0x000000000df02e89 hasDeducedReturnType(clang::FunctionDecl*) /home/xxx/data/git/llvm-project/clang/lib/Sema/SemaStmt.cpp:3261:0
#&#8203;10 0x000000000df02e89 clang::Sema::ActOnCapScopeReturnStmt(clang::SourceLocation, clang::Expr*) /home/xxx/data/git/llvm-project/clang/lib/Sema/SemaStmt.cpp:3276:0
#&#8203;11 0x000000000df10e3a clang::Sema::BuildReturnStmt(clang::SourceLocation, clang::Expr*) /home/xxx/data/git/llvm-project/clang/lib/Sema/SemaStmt.cpp:3616:12
#&#8203;12 0x000000000df1077c clang::ActionResult<clang::Stmt*, true>::isInvalid() const /home/xxx/data/git/llvm-project/clang/include/clang/Sema/Ownership.h:0:0
#&#8203;13 0x000000000df1077c clang::Sema::ActOnReturnStmt(clang::SourceLocation, clang::Expr*, clang::Scope*) /home/xxx/data/git/llvm-project/clang/lib/Sema/SemaStmt.cpp:3594:0
#&#8203;14 0x000000000ca17cba clang::Parser::ParseReturnStatement() /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:0:18
#&#8203;15 0x000000000ca09527 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::Parser::ParsedAttributesWithRange&) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:282:11
#&#8203;16 0x000000000ca081a6 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:106:20
#&#8203;17 0x000000000ca1c77e clang::Parser::ParseCompoundStatementBody(bool) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:1089:11
#&#8203;18 0x000000000ca1a464 clang::Parser::ParseScope::~ParseScope() /home/xxx/data/git/llvm-project/clang/include/clang/Parse/Parser.h:0:0
#&#8203;19 0x000000000ca1a464 clang::Parser::ParseCompoundStatement(bool, unsigned int) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:904:0
#&#8203;20 0x000000000c91556d clang::Parser::ParseParenExpression(clang::Parser::ParenParseOption&, bool, bool, clang::OpaquePtr<clang::QualType>&, clang::SourceLocation&) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExpr.cpp:2872:16
#&#8203;21 0x000000000c90fc2e clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExpr.cpp:957:11
#&#8203;22 0x000000000c902c60 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExpr.cpp:681:20
#&#8203;23 0x000000000c8fe5ef clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExpr.cpp:176:10
#&#8203;24 0x000000000c8627aa _ZN4llvm12function_refIFN5clang12ActionResultIPNS1_4ExprELb1EEES4_EEC2IZNS1_4Sema25CorrectDelayedTyposInExprES5_PNS1_7VarDeclEbS7_Ed_UlS4_E_EEOT_PNSt9enable_ifIXntsr3std7is_sameINSt9remove_cvINSt16remove_referenceISD_E4typeEE4typeES7_EE5valueEvE4typeE /home/xxx/data/git/llvm-project/llvm/include/llvm/ADT/STLExtras.h:0:0
#&#8203;25 0x000000000c8627aa clang::Parser::ParseAttributeArgsCommon(clang::IdentifierInfo*, clang::SourceLocation, clang::ParsedAttributes&, clang::SourceLocation*, clang::IdentifierInfo*, clang::SourceLocation, clang::AttributeCommonInfo::Syntax) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:397:0
#&#8203;26 0x000000000c86049b clang::Parser::ParseGNUAttributeArgs(clang::IdentifierInfo*, clang::SourceLocation, clang::ParsedAttributes&, clang::SourceLocation*, clang::IdentifierInfo*, clang::SourceLocation, clang::AttributeCommonInfo::Syntax, clang::Declarator*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:480:3
#&#8203;27 0x000000000c85ed4a clang::Parser::ParseGNUAttributes(clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::LateParsedAttrList*, clang::Declarator*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:189:9
#&#8203;28 0x000000000c93d177 clang::Parser::MaybeParseGNUAttributes(clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::LateParsedAttrList*) /home/xxx/data/git/llvm-project/clang/include/clang/Parse/Parser.h:2658:3
#&#8203;29 0x000000000c93d177 clang::Parser::ParseLambdaExpressionAfterIntroducer(clang::LambdaIntroducer&) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExprCXX.cpp:1322:0
#&#8203;30 0x000000000c939030 clang::Parser::ParseLambdaExpression() /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExprCXX.cpp:739:10
#&#8203;31 0x000000000c90f457 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExpr.cpp:1764:13
#&#8203;32 0x000000000c902c60 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExpr.cpp:681:20
#&#8203;33 0x000000000c8fe5ef clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseExpr.cpp:176:10
#&#8203;34 0x000000000c885bb1 clang::Parser::ParseInitializer() /home/xxx/data/git/llvm-project/clang/include/clang/Parse/Parser.h:0:14
#&#8203;35 0x000000000c885bb1 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:2232:0
#&#8203;36 0x000000000c880fc7 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:1986:9
#&#8203;37 0x000000000c8739fc clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::Parser::ParsedAttributesWithRange&, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:1700:10
#&#8203;38 0x000000000c873179 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::Parser::ParsedAttributesWithRange&, clang::SourceLocation*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:0:12
#&#8203;39 0x000000000ca08d41 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::Parser::ParsedAttributesWithRange&) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:0:13
#&#8203;40 0x000000000ca081a6 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:106:20
#&#8203;41 0x000000000ca1c77e clang::Parser::ParseCompoundStatementBody(bool) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:1089:11
#&#8203;42 0x000000000ca1f748 clang::ActionResult<clang::Stmt*, true>::isInvalid() const /home/xxx/data/git/llvm-project/clang/include/clang/Sema/Ownership.h:0:0
#&#8203;43 0x000000000ca1f748 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseStmt.cpp:2240:0
#&#8203;44 0x000000000c833117 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) /home/xxx/data/git/llvm-project/clang/lib/Parse/Parser.cpp:1339:10
#&#8203;45 0x000000000c88224e clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseDecl.cpp:1926:18
#&#8203;46 0x000000000c83020d clang::Parser::ParseDeclOrFunctionDefInternal(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec&, clang::AccessSpecifier) /home/xxx/data/git/llvm-project/clang/lib/Parse/Parser.cpp:0:10
#&#8203;47 0x000000000c82e939 clang::Parser::ObjCDeclContextSwitch::~ObjCDeclContextSwitch() /home/xxx/data/git/llvm-project/clang/include/clang/Parse/Parser.h:0:0
#&#8203;48 0x000000000c82e939 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*, clang::AccessSpecifier) /home/xxx/data/git/llvm-project/clang/lib/Parse/Parser.cpp:1116:0
#&#8203;49 0x000000000c82c6a1 clang::Parser::ParseExternalDeclaration(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) /home/xxx/data/git/llvm-project/clang/lib/Parse/Parser.cpp:935:12
#&#8203;50 0x000000000c827ecc clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool) /home/xxx/data/git/llvm-project/clang/lib/Parse/Parser.cpp:683:10
#&#8203;51 0x000000000c826ccc clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&) /home/xxx/data/git/llvm-project/clang/lib/Parse/Parser.cpp:555:26
#&#8203;52 0x000000000c81cf4a clang::ParseAST(clang::Sema&, bool, bool) /home/xxx/data/git/llvm-project/clang/lib/Parse/ParseAST.cpp:157:15
#&#8203;53 0x000000000861c2a2 clang::ASTFrontendAction::ExecuteAction() /home/xxx/data/git/llvm-project/clang/lib/Frontend/FrontendAction.cpp:1059:1
#&#8203;54 0x00000000099decd8 clang::CodeGenAction::ExecuteAction() /home/xxx/data/git/llvm-project/clang/lib/CodeGen/CodeGenAction.cpp:1184:28
#&#8203;55 0x000000000861a51a clang::FrontendAction::Execute() /home/xxx/data/git/llvm-project/clang/lib/Frontend/FrontendAction.cpp:954:10
#&#8203;56 0x000000000854eaa7 llvm::Error::operator bool() /home/xxx/data/git/llvm-project/llvm/include/llvm/Support/Error.h:0:0
#&#8203;57 0x000000000854eaa7 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) /home/xxx/data/git/llvm-project/clang/lib/Frontend/CompilerInstance.cpp:984:0
#&#8203;58 0x00000000088f183f clang::CompilerInstance::getFrontendOpts() /home/xxx/data/git/llvm-project/clang/include/clang/Frontend/CompilerInstance.h:0:0
#&#8203;59 0x00000000088f183f clang::ExecuteCompilerInvocation(clang::CompilerInstance*) /home/xxx/data/git/llvm-project/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:279:0
#&#8203;60 0x0000000000b094cc llvm::TimeTraceScope::~TimeTraceScope() /home/xxx/data/git/llvm-project/llvm/include/llvm/Support/TimeProfiler.h:0:0
#&#8203;61 0x0000000000b094cc cc1_main(llvm::ArrayRef<char const*>, char const*, void*) /home/xxx/data/git/llvm-project/clang/tools/driver/cc1_main.cpp:241:0
#&#8203;62 0x0000000000afaf3b ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) /home/xxx/data/git/llvm-project/clang/tools/driver/driver.cpp:330:12
#&#8203;63 0x0000000000af6966 main /home/xxx/data/git/llvm-project/clang/tools/driver/driver.cpp:407:12
#&#8203;64 0x00007f0e741d0b97 __libc_start_main /build/glibc-2ORdQG/glibc-2.27/csu/../csu/libc-start.c:344:0
#&#8203;65 0x0000000000af38ea _start (/data/xxx/git/llvm-project/build/bin/clang-11+0xaf38ea)
clang-11: error: unable to execute command: Segmentation fault (core dumped)
clang-11: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 11.1.0 (https://github.com/llvm/llvm-project.git 1fdec59bffc11ae37eb51a1b9869f0696bfd5312)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /data/xxx/git/llvm-project/build/bin
clang-11: note: diagnostic msg:
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang-11: note: diagnostic msg: /tmp/test-398094.cpp
clang-11: note: diagnostic msg: /tmp/test-398094.sh
clang-11: note: diagnostic msg:

********************

[fhahn]

Also crashes on trunk https://godbolt.org/z/v17hqr

0.	Program arguments: /opt/compiler-explorer/clang-trunk/bin/clang++ -g -o ./output.s -mllvm --x86-asm-syntax=intel -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics <source>
1.	<source>:3:13: current parser token ';'
2.	<source>:1:12: parsing function body 'main'
3.	<source>:1:12: in compound statement ('{}')
4.	<source>:2:14: lambda expression parsing
5.	<source>:2:40: in compound statement ('{}')
 #&#8203;0 0x000055d1894d7bec llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x303ebec)
 #&#8203;1 0x000055d1894d5994 llvm::sys::RunSignalHandlers() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x303c994)
 #&#8203;2 0x000055d1894d5c15 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x303cc15)
 #&#8203;3 0x000055d18943c5b8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #&#8203;4 0x00007fe9f6b523c0 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x153c0)
 #&#8203;5 0x000055d18b776c17 clang::Sema::ActOnCapScopeReturnStmt(clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x52ddc17)
 #&#8203;6 0x000055d18b77763f clang::Sema::BuildReturnStmt(clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x52de63f)
 #&#8203;7 0x000055d18b7785a2 clang::Sema::ActOnReturnStmt(clang::SourceLocation, clang::Expr*, clang::Scope*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x52df5a2)
 #&#8203;8 0x000055d18b1bf775 clang::Parser::ParseReturnStatement() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d26775)
 #&#8203;9 0x000055d18b1c270f clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::Parser::ParsedAttributesWithRange&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d2970f)
#&#8203;10 0x000055d18b1c2dcd clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d29dcd)
#&#8203;11 0x000055d18b1c38e1 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d2a8e1)
#&#8203;12 0x000055d18b1c40be clang::Parser::ParseCompoundStatement(bool, unsigned int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d2b0be)
#&#8203;13 0x000055d18b1700ee clang::Parser::ParseParenExpression(clang::Parser::ParenParseOption&, bool, bool, clang::OpaquePtr<clang::QualType>&, clang::SourceLocation&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4cd70ee)
#&#8203;14 0x000055d18b167cce clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ccecce)
#&#8203;15 0x000055d18b169fb6 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4cd0fb6)
#&#8203;16 0x000055d18b16b174 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4cd2174)
#&#8203;17 0x000055d18b13b1c6 clang::Parser::ParseAttributeArgsCommon(clang::IdentifierInfo*, clang::SourceLocation, clang::ParsedAttributes&, clang::SourceLocation*, clang::IdentifierInfo*, clang::SourceLocation, clang::AttributeCommonInfo::Syntax) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ca21c6)
#&#8203;18 0x000055d18b13d74c clang::Parser::ParseGNUAttributeArgs(clang::IdentifierInfo*, clang::SourceLocation, clang::ParsedAttributes&, clang::SourceLocation*, clang::IdentifierInfo*, clang::SourceLocation, clang::AttributeCommonInfo::Syntax, clang::Declarator*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ca474c)
#&#8203;19 0x000055d18b13dcc6 clang::Parser::ParseGNUAttributes(clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::LateParsedAttrList*, clang::Declarator*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ca4cc6)
#&#8203;20 0x000055d18b13edee clang::Parser::ParseAttributes(unsigned int, clang::Parser::ParsedAttributesWithRange&, clang::SourceLocation*, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ca5dee)
#&#8203;21 0x000055d18b17fe06 clang::Parser::ParseLambdaExpressionAfterIntroducer(clang::LambdaIntroducer&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ce6e06)
#&#8203;22 0x000055d18b180523 clang::Parser::ParseLambdaExpression() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ce7523)
#&#8203;23 0x000055d18b168b83 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4ccfb83)
#&#8203;24 0x000055d18b169fb6 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4cd0fb6)
#&#8203;25 0x000055d18b16b174 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4cd2174)
#&#8203;26 0x000055d18b136de7 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4c9dde7)
#&#8203;27 0x000055d18b147975 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4cae975)
#&#8203;28 0x000055d18b14855d clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::Parser::ParsedAttributesWithRange&, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4caf55d)
#&#8203;29 0x000055d18b148882 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::Parser::ParsedAttributesWithRange&, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4caf882)
#&#8203;30 0x000055d18b1c2b59 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::Parser::ParsedAttributesWithRange&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d29b59)
#&#8203;31 0x000055d18b1c2dcd clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d29dcd)
#&#8203;32 0x000055d18b1c38e1 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d2a8e1)
#&#8203;33 0x000055d18b1c7103 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4d2e103)
#&#8203;34 0x000055d18b11f267 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4c86267)
#&#8203;35 0x000055d18b147885 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4cae885)
#&#8203;36 0x000055d18b11a9c1 clang::Parser::ParseDeclOrFunctionDefInternal(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4c819c1)
#&#8203;37 0x000055d18b11b0f1 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (.part.241) Parser.cpp:0:0
#&#8203;38 0x000055d18b121079 clang::Parser::ParseExternalDeclaration(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4c88079)
#&#8203;39 0x000055d18b1225f9 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4c895f9)
#&#8203;40 0x000055d18b122be5 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4c89be5)
#&#8203;41 0x000055d18b115823 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4c7c823)
#&#8203;42 0x000055d18a34d932 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3eb4932)
#&#8203;43 0x000055d189d4c9b1 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x38b39b1)
#&#8203;44 0x000055d189ce35f3 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x384a5f3)
#&#8203;45 0x000055d189e13a13 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x397aa13)
#&#8203;46 0x000055d18747f91c cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xfe691c)
#&#8203;47 0x000055d18747ba3d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#&#8203;48 0x000055d189b9a0f5 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#&#8203;49 0x000055d18943c693 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x2fa3693)
#&#8203;50 0x000055d189b9aa28 clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, bool*) const (.part.165) Job.cpp:0:0
#&#8203;51 0x000055d189b73b29 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x36dab29)
#&#8203;52 0x000055d189b74d4f clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*> >&) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x36dbd4f)
#&#8203;53 0x000055d189b84a95 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*> >&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x36eba95)
#&#8203;54 0x000055d187399dd4 main (/opt/compiler-explorer/clang-trunk/bin/clang+++0xf00dd4)
#&#8203;55 0x00007fe9f66030b3 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b3)
#&#8203;56 0x000055d18747b5ba _start (/opt/compiler-explorer/clang-trunk/bin/clang+++0xfe25ba)
clang-13: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Compiler returned: 139

[Endilll]

Still crashing as of post-17 trunk: https://godbolt.org/z/54YrjjK6W

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 <source>
1.	<source>:3:13: current parser token ';'
2.	<source>:1:12: parsing function body 'main'
3.	<source>:1:12: in compound statement ('{}')
4.	<source>:2:14: lambda expression parsing
5.	<source>:2:40: in compound statement ('{}')
 #0 0x00000000036afc28 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36afc28)
 #1 0x00000000036ad8ec llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x36ad8ec)
 #2 0x00000000035f6d08 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f3eceae2420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00000000067534bc clang::Sema::ActOnCapScopeReturnStmt(clang::SourceLocation, clang::Expr*, clang::Sema::NamedReturnInfo&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67534bc)
 #5 0x0000000006753fa1 clang::Sema::BuildReturnStmt(clang::SourceLocation, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6753fa1)
 #6 0x00000000067565df clang::Sema::ActOnReturnStmt(clang::SourceLocation, clang::Expr*, clang::Scope*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67565df)
 #7 0x0000000005ee0847 clang::Parser::ParseReturnStatement() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ee0847)
 #8 0x0000000005ee3b2b 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+++0x5ee3b2b)
 #9 0x0000000005ee5128 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ee5128)
#10 0x0000000005ee6069 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ee6069)
#11 0x0000000005ee7a9a clang::Parser::ParseCompoundStatement(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ee7a9a)
#12 0x0000000005e77152 clang::Parser::ParseParenExpression(clang::Parser::ParenParseOption&, bool, bool, clang::OpaquePtr<clang::QualType>&, clang::SourceLocation&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e77152)
#13 0x0000000005e6bc25 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6bc25)
#14 0x0000000005e6dc9a clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6dc9a)
#15 0x0000000005e6de39 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6de39)
#16 0x0000000005e2bed2 clang::Parser::ParseAttributeArgumentList(clang::IdentifierInfo const&, llvm::SmallVectorImpl<clang::Expr*>&, clang::ParsedAttributeArgumentsProperties) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e2bed2)
#17 0x0000000005e32b1c clang::Parser::ParseAttributeArgsCommon(clang::IdentifierInfo*, clang::SourceLocation, clang::ParsedAttributes&, clang::SourceLocation*, clang::IdentifierInfo*, clang::SourceLocation, clang::AttributeCommonInfo::Form) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e32b1c)
#18 0x0000000005e36a13 clang::Parser::ParseGNUAttributeArgs(clang::IdentifierInfo*, clang::SourceLocation, clang::ParsedAttributes&, clang::SourceLocation*, clang::IdentifierInfo*, clang::SourceLocation, clang::AttributeCommonInfo::Form, clang::Declarator*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e36a13)
#19 0x0000000005e374e8 clang::Parser::ParseGNUAttributes(clang::ParsedAttributes&, clang::Parser::LateParsedAttrList*, clang::Declarator*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e374e8)
#20 0x0000000005e3a488 clang::Parser::ParseAttributes(unsigned int, clang::ParsedAttributes&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e3a488)
#21 0x0000000005e81e09 clang::Parser::ParseLambdaExpressionAfterIntroducer(clang::LambdaIntroducer&)::'lambda0'()::operator()() const ParseExprCXX.cpp:0:0
#22 0x0000000005e8d44d clang::Parser::ParseLambdaExpressionAfterIntroducer(clang::LambdaIntroducer&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e8d44d)
#23 0x0000000005e8df5b clang::Parser::ParseLambdaExpression() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e8df5b)
#24 0x0000000005e6c305 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6c305)
#25 0x0000000005e6dc9a clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6dc9a)
#26 0x0000000005e6de39 clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e6de39)
#27 0x0000000005e2e5bd clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e2e5bd)
#28 0x0000000005e3c040 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e3c040)
#29 0x0000000005e44395 clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e44395)
#30 0x0000000005e44837 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e44837)
#31 0x0000000005ee4420 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+++0x5ee4420)
#32 0x0000000005ee5128 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ee5128)
#33 0x0000000005ee6069 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ee6069)
#34 0x0000000005ee798a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5ee798a)
#35 0x0000000005e15151 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e15151)
#36 0x0000000005e3c748 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e3c748)
#37 0x0000000005e0906b clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e0906b)
#38 0x0000000005e0979f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (.part.0) Parser.cpp:0:0
#39 0x0000000005e0feb4 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e0feb4)
#40 0x0000000005e106bd clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e106bd)
#41 0x0000000005e10af0 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e10af0)
#42 0x0000000005e049e2 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x5e049e2)
#43 0x000000000490f578 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x490f578)
#44 0x0000000004177f89 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4177f89)
#45 0x00000000040f818e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x40f818e)
#46 0x00000000042561fe clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42561fe)
#47 0x0000000000bd6ea0 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd6ea0)
#48 0x0000000000bcf0ca ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#49 0x0000000003f59309 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
#50 0x00000000035f71b4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x35f71b4)
#51 0x0000000003f598ff 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
#52 0x0000000003f21c85 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f21c85)
#53 0x0000000003f226ed 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+++0x3f226ed)
#54 0x0000000003f2a615 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f2a615)
#55 0x0000000000bd4cac clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbd4cac)
#56 0x0000000000ad14a1 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xad14a1)
#57 0x00007f3ece586083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#58 0x0000000000bcebae _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbcebae)
clang++: error: clang frontend command failed with exit code 139 (use -v to see invocation)

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[shafik]

This looks tough, so we are parsing the lambda and get to Parser::ParseAttributeArgumentList(...) here:

llvm-project/clang/lib/Parse/ParseDecl.cpp

Line 415 in 61c44f1

Expr = ParseAssignmentExpression();

I think b/c it just has to be a balance token sequence. We eventually get here:

llvm-project/clang/lib/Sema/SemaStmt.cpp

Lines 3947 to 3949 in 0649594

	if (isa<CapturingScopeInfo>(getCurFunction()))
	return ActOnCapScopeReturnStmt(ReturnLoc, RetValExp, NRInfo,
	SupressSimplerImplicitMoves);

so we know we are parsing a lambda IIUC but we don't realize that being here does not make sense when parsing attribute argument list and therefore can't error out.

CC @zygoloid @cor3ntin for possible advice on tackling this one

[cor3ntin]

Lambdas do not have types until after the declarator is parsed.
BuildReturnStmt do seem to be fairly protected against null types.

However, ActOnCapScopeReturnStmt calls

static bool hasDeducedReturnType(FunctionDecl *FD) {
  const FunctionProtoType *FPT =
      FD->getTypeSourceInfo()->getType()->castAs<FunctionProtoType>();
  return FPT->getReturnType()->isUndeducedType();
}

Adding

 if(CurLambda && CurLambda->CallOperator->getType().isNull()) {
    return StmtError();
 }

at the very top of ActOnCapScopeReturnStmt does fix the crash and produces an error similar to what we get for functions
ie,

void test () {
  struct S {
    int f() __attribute__((b(({
        return 0;
    }
};
}

[cor3ntin]

I don't have the bandwidth to make a pr, but with the above guidance, it should be straightforward

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

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[pfusik]

[](void)__attribute__((b(({

is a lambda with no parameters and a GCC-style attribute b. There is one argument for the b attribute, which is a GCC extension statement expression ({ return 0; }).

Note that statement expressions have the value of their last statement.

The following is accepted by both GCC and Clang:

char *__attribute__((aligned(({ 8; })))) *f;

It is unclear to me how to treat non-local control flow (return, break etc) in statement expressions in attributes. It probably should be a compile-time error, however GCC accepts:

[]()__attribute__((b(({ return 0; })))){};

For now, I created https://reviews.llvm.org/D159528 as per the above instructions. Should I file a GH PR instead?

[pfusik]

The issue is not specific to GCC-style attributes and is also reproducible with C++11 attributes.