Clang crash in CheckArrayAccess; division by zero

[bevin-hansson]

Clang crashes on the following (very reduced) example:

a[][0] int b = a[217727][0]

Building this with -target avr causes a crash:

 #0 0x00005594ccd5d8df llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x3ba18df)
 #1 0x00005594ccd5b90c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x3b9f90c)
 #2 0x00005594cccae518 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007fdafa17c420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00005594ccc8bb35 llvm::APInt::udiv(llvm::APInt const&) const (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x3acfb35)
 #5 0x00005594cf443478 clang::Sema::CheckArrayAccess(clang::Expr const*, clang::Expr const*, clang::ArraySubscriptExpr const*, bool, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x6287478)
 #6 0x00005594cf443bd8 clang::Sema::CheckArrayAccess(clang::Expr const*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x6287bd8)
 #7 0x00005594cf48df7c clang::Sema::CheckCompletedExpr(clang::Expr*, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x62d1f7c)
 #8 0x00005594cf8ff3f2 clang::Sema::ActOnFinishFullExpr(clang::Expr*, clang::SourceLocation, bool, bool, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x67433f2)
 #9 0x00005594cf5dccf8 clang::Sema::AddInitializerToDecl(clang::Decl*, clang::Expr*, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x6420cf8)
#10 0x00005594cf29c68d clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x60e068d)
#11 0x00005594cf2b01b6 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x60f41b6)
#12 0x00005594cf279617 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x60bd617)
#13 0x00005594cf27a75f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (.part.0) Parser.cpp:0:0
#14 0x00005594cf282194 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x60c6194)
#15 0x00005594cf28372d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x60c772d)
#16 0x00005594cf272a8a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x60b6a8a)
#17 0x00005594ce04d865 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x4e91865)
#18 0x00005594cd929671 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x476d671)
#19 0x00005594cd8ad993 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x46f1993)
#20 0x00005594cda0db3b clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x4851b3b)
#21 0x00005594ca53641c cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x137a41c)
#22 0x00005594ca531bdc ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#23 0x00005594cd70ece9 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
#24 0x00005594cccae977 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x3af2977)
#25 0x00005594cd70ef1c 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
#26 0x00005594cd6d73fc clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x451b3fc)
#27 0x00005594cd6d7ded clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x451bded)
#28 0x00005594cd6e223c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x452623c)
#29 0x00005594ca534523 clang_main(int, char**) (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x1378523)
#30 0x00007fdaf9c2a083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#31 0x00005594ca52dd1e _start (/opt/compiler-explorer/clang-16.0.0/bin/clang+0x1371d1e)

See the following Godbolt: https://godbolt.org/z/WdEqPWad9

The Godbolt compiler doesn't give an assertion, but when running with a debug build, you get

clang: ../lib/Support/APInt.cpp:1584: llvm::APInt llvm::APInt::udiv(const llvm::APInt&) const: Assertion `RHS.U.VAL != 0 && "Divide by zero?"' failed.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[benshi001]

A crash log with more details

 #7 0x00007ff2704c2acf raise (/lib64/libc.so.6+0x4eacf)
 #8 0x00007ff270495ea5 abort (/lib64/libc.so.6+0x21ea5)
 #9 0x00007ff270495d79 _nl_load_domain.cold.0 (/lib64/libc.so.6+0x21d79)
#10 0x00007ff2704bb426 (/lib64/libc.so.6+0x47426)
#11 0x000000000424a6d2 llvm::APInt::udiv(llvm::APInt const&) const /data/home/bennshi/work/llvm-project/llvm/lib/Support/APInt.cpp:1585:30
#12 0x0000000007eab5ff clang::Sema::CheckArrayAccess(clang::Expr const*, clang::Expr const*, clang::ArraySubscriptExpr const*, bool, bool) /data/home/bennshi/work/llvm-project/clang/lib/Sema/SemaChecking.cpp:17171:41
#13 0x0000000007eac259 clang::Sema::CheckArrayAccess(clang::Expr const*) /data/home/bennshi/work/llvm-project/clang/lib/Sema/SemaChecking.cpp:17308:28
#14 0x0000000007ea638c clang::Sema::CheckImplicitConversions(clang::Expr*, clang::SourceLocation) /data/home/bennshi/work/llvm-project/clang/lib/Sema/SemaChecking.cpp:15743:29
#15 0x0000000007ea94e9 clang::Sema::CheckCompletedExpr(clang::Expr*, clang::SourceLocation, bool) /data/home/bennshi/work/llvm-project/clang/lib/Sema/SemaChecking.cpp:16674:35
#16 0x000000000861daed clang::Sema::ActOnFinishFullExpr(clang::Expr*, clang::SourceLocation, bool, bool, bool) /data/home/bennshi/work/llvm-project/clang/lib/Sema/SemaExprCXX.cpp:8882:19
#17 0x0000000008067a59 clang::Sema::AddInitializerToDecl(clang::Decl*, clang::Expr*, bool) /data/home/bennshi/work/llvm-project/clang/lib/Sema/SemaDecl.cpp:13503:73
#18 0x0000000007c82335 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) /data/home/bennshi/work/llvm-project/clang/lib/Parse/ParseDecl.cpp:2555:37
#19 0x0000000007c80f15 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) /data/home/bennshi/work/llvm-project/clang/lib/Parse/ParseDecl.cpp:2264:65
#20 0x0000000007c60356 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) /data/home/bennshi/work/llvm-project/clang/lib/Parse/Parser.cpp:1215:1
#21 0x0000000007c60431 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) /data/home/bennshi/work/llvm-project/clang/lib/Parse/Parser.cpp:1229:72
#22 0x0000000007c5f7cf clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) /data/home/bennshi/work/llvm-project/clang/lib/Parse/Parser.cpp:1040:75
#23 0x0000000007c5e6ce clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) /data/home/bennshi/work/llvm-project/clang/lib/Parse/Parser.cpp:742:61
#24 0x0000000007c59a8a clang::ParseAST(clang::Sema&, bool, bool) /data/home/bennshi/work/llvm-project/clang/lib/Parse/ParseAST.cpp:163:37
#25 0x00000000051b9fb5 clang::ASTFrontendAction::ExecuteAction() /data/home/bennshi/work/llvm-project/clang/lib/Frontend/FrontendAction.cpp:1173:11
#26 0x0000000005b1a0f9 clang::CodeGenAction::ExecuteAction() /data/home/bennshi/work/llvm-project/clang/lib/CodeGen/CodeGenAction.cpp:1208:5
#27 0x00000000051b98e1 clang::FrontendAction::Execute() /data/home/bennshi/work/llvm-project/clang/lib/Frontend/FrontendAction.cpp:1067:38
#28 0x00000000050f27fa clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) /data/home/bennshi/work/llvm-project/clang/lib/Frontend/CompilerInstance.cpp:1054:42
#29 0x0000000005348232 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) /data/home/bennshi/work/llvm-project/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:272:38
#30 0x00000000029bd334 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) /data/home/bennshi/work/llvm-project/clang/tools/driver/cc1_main.cpp:249:40
#31 0x00000000029aec75 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) /data/home/bennshi/work/llvm-project/clang/tools/driver/driver.cpp:366:20
#32 0x00000000029aee49 clang_main(int, char**, llvm::ToolContext const&)::'lambda'(llvm::SmallVectorImpl<char const*>&)::operator()(llvm::SmallVectorImpl<char const*>&) const /data/home/bennshi/work/llvm-project/clang/tools/driver/driver.cpp:507:5
#33 0x00000000029b03f7 int llvm::function_ref<int (llvm::SmallVectorImpl<char const*>&)>::callback_fn<clang_main(int, char**, llvm::ToolContext const&)::'lambda'(llvm::SmallVectorImpl<char const*>&)>(long, llvm::SmallVectorImpl<char const*>&) /data/home/bennshi/work/llvm-project/llvm/include/llvm/ADT/STLFunctionalExtras.h:47:3
#34 0x0000000004fa2bdf llvm::function_ref<int (llvm::SmallVectorImpl<char const*>&)>::operator()(llvm::SmallVectorImpl<char const*>&) const /data/home/bennshi/work/llvm-project/llvm/include/llvm/ADT/STLFunctionalExtras.h:69:3
#35 0x0000000004fa19fd 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'()::operator()() const /data/home/bennshi/work/llvm-project/clang/lib/Driver/Job.cpp:440:32
#36 0x0000000004fa1e22 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) /data/home/bennshi/work/llvm-project/llvm/include/llvm/ADT/STLFunctionalExtras.h:46:40
#37 0x00000000031dda70 llvm::function_ref<void ()>::operator()() const /data/home/bennshi/work/llvm-project/llvm/include/llvm/ADT/STLFunctionalExtras.h:68:62
#38 0x0000000004273b01 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) /data/home/bennshi/work/llvm-project/llvm/lib/Support/CrashRecoveryContext.cpp:427:10
#39 0x0000000004fa1bea clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const /data/home/bennshi/work/llvm-project/clang/lib/Driver/Job.cpp:440:7
#40 0x0000000004f448e4 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const /data/home/bennshi/work/llvm-project/clang/lib/Driver/Compilation.cpp:199:22
#41 0x0000000004f44c1d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const /data/home/bennshi/work/llvm-project/clang/lib/Driver/Compilation.cpp:253:62
#42 0x0000000004f564d8 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) /data/home/bennshi/work/llvm-project/clang/lib/Driver/Driver.cpp:1896:28
#43 0x00000000029affa8 clang_main(int, char**, llvm::ToolContext const&) /data/home/bennshi/work/llvm-project/clang/tools/driver/driver.cpp:542:39
#44 0x00000000029dc7ef main /data/home/bennshi/work/llvm-project/build/tools/clang/tools/driver/clang-driver.cpp:15:58
#45 0x00007ff2704aed85 __libc_start_main (/lib64/libc.so.6+0x3ad85)
#46 0x00000000029ad2ae _start (./bin/clang+0x29ad2ae)
clang: error: clang frontend command failed with exit code 134 (use -v to see invocation)
clang version 18.0.0 (git@github.com:llvm/llvm-project.git 88fbccd7ffcc1f99f7f52dbdfe82438b880a976e)
Target: avr
Thread model: posix
InstalledDir: /data/home/bennshi/work/llvm-project/build/./bin
clang: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang: note: diagnostic msg: /tmp/a-c0a197.c
clang: note: diagnostic msg: /tmp/a-c0a197.sh
clang: note: diagnostic msg: 

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

[danix800]

Confirmed. This is not AVR specific, any array index exceeding addr space would trigger this crash:

// -target i686

int a[][0];
void test() {
  int b = a[0x100000000][0]; // 0x100000000 needs 33 bits > 32 bits on i686
}

Bound checking on array of zero-length element isn't meaningful. See https://reviews.llvm.org/D157584