Compiler null dereference on invalid implicit conversion between incompatible checked pointer types

[mattmccutchen-cci]

Another low-priority issue for the record. Compiling the following code:

#pragma CHECKED_SCOPE on

int main(void) {
  _Array_ptr<void> pv = 0;
  _Array_ptr<_Ptr<int>> ppi = 0;
  ppi = pv;
  return 0;
}

crashes the compiler as follows:

casts-compiler-crash.c:6:7: error: implicit conversion between '_Array_ptr<void>' and '_Array_ptr<_Ptr<int>>' is not allowed in a checked scope because '_Ptr<int>' contains or is a checked pointer
  ppi = pv;
      ^
PLEASE submit a bug report to https://github.com/Microsoft/checkedc-clang/issues and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /home/matt/3c/build/bin/clang -c -o /dev/null casts-compiler-crash.c 
1.	casts-compiler-crash.c:6:11: current parser token ';'
2.	casts-compiler-crash.c:3:16: parsing function body 'main'
3.	casts-compiler-crash.c:3:16: in compound statement ('{}')
 #0 0x0000562f8ef8122b llvm::sys::PrintStackTrace(llvm::raw_ostream&) /home/matt/3c/llvm/lib/Support/Unix/Signals.inc:564:22
 #1 0x0000562f8ef8129e PrintStackTraceSignalHandler(void*) /home/matt/3c/llvm/lib/Support/Unix/Signals.inc:625:1
 #2 0x0000562f8ef7ed8a llvm::sys::RunSignalHandlers() /home/matt/3c/llvm/lib/Support/Signals.cpp:68:20
 #3 0x0000562f8ef7ef89 llvm::sys::CleanupOnSignal(unsigned long) /home/matt/3c/llvm/lib/Support/Unix/Signals.inc:361:31
 #4 0x0000562f8eed2264 HandleCrash /home/matt/3c/llvm/lib/Support/CrashRecoveryContext.cpp:75:27
 #5 0x0000562f8eed2264 CrashRecoverySignalHandler(int) /home/matt/3c/llvm/lib/Support/CrashRecoveryContext.cpp:382:62
 #6 0x00007f67092663c0 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x153c0)
 #7 0x0000562f91d75e71 clang::Sema::DiagnoseAssignmentResult(clang::Sema::AssignConvertType, clang::SourceLocation, clang::QualType, clang::QualType, clang::Expr*, clang::Sema::AssignmentAction, bool*) /home/matt/3c/clang/lib/Sema/SemaExpr.cpp:16720:17
 #8 0x0000562f91d94400 clang::Sema::CheckAssignmentOperands(clang::Expr*, clang::ActionResult<clang::Expr*, true>&, clang::SourceLocation, clang::QualType) /home/matt/3c/clang/lib/Sema/SemaExpr.cpp:13513:3
 #9 0x0000562f91d9d868 clang::Sema::CreateBuiltinBinOp(clang::SourceLocation, clang::BinaryOperatorKind, clang::Expr*, clang::Expr*) /home/matt/3c/clang/lib/Sema/SemaExpr.cpp:14440:73
#10 0x0000562f91d9edd5 clang::Sema::BuildBinOp(clang::Scope*, clang::SourceLocation, clang::BinaryOperatorKind, clang::Expr*, clang::Expr*) /home/matt/3c/clang/lib/Sema/SemaExpr.cpp:15014:57
#11 0x0000562f91d9ee40 clang::Sema::ActOnBinOp(clang::Scope*, clang::SourceLocation, clang::tok::TokenKind, clang::Expr*, clang::Expr*) /home/matt/3c/clang/lib/Sema/SemaExpr.cpp:14867:1
#12 0x0000562f91426f15 clang::Parser::ParseRHSOfBinaryExpression(clang::ActionResult<clang::Expr*, true>, clang::prec::Level) (.localalias) /home/matt/3c/clang/lib/Parse/ParseExpr.cpp:632:71
#13 0x0000562f91427e8a clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) /home/matt/3c/clang/lib/Parse/ParseExpr.cpp:179:1
#14 0x0000562f91427351 clang::Parser::ParseExpression(clang::Parser::TypeCastState) /home/matt/3c/clang/lib/Parse/ParseExpr.cpp:124:54
#15 0x0000562f9145fc3e clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) /home/matt/3c/clang/lib/Parse/ParseStmt.cpp:478:3
#16 0x0000562f9145df7c clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::Parser::ParsedAttributesWithRange&) /home/matt/3c/clang/lib/Parse/ParseStmt.cpp:247:38
#17 0x0000562f9145e78d clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) /home/matt/3c/clang/lib/Parse/ParseStmt.cpp:107:45
#18 0x0000562f91463ebc clang::Parser::ParseCompoundStatementBody(bool, clang::CheckedScopeSpecifier, clang::SourceLocation, clang::SourceLocation) /home/matt/3c/clang/lib/Parse/ParseStmt.cpp:1172:56
#19 0x0000562f91465e53 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&, clang::CheckedScopeSpecifier) /home/matt/3c/clang/lib/Parse/ParseStmt.cpp:2322:70
#20 0x0000562f913c9106 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) /home/matt/3c/clang/lib/Parse/Parser.cpp:1400:36
#21 0x0000562f913e65a2 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) /home/matt/3c/clang/lib/Parse/ParseDecl.cpp:2013:36
#22 0x0000562f913c3888 clang::Sema::CheckedScopeRAII::~CheckedScopeRAII() /home/matt/3c/clang/include/clang/Sema/Sema.h:4427:28
#23 0x0000562f913c3888 clang::Parser::ParseDeclOrFunctionDefInternal(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec&, clang::AccessSpecifier) /home/matt/3c/clang/lib/Parse/Parser.cpp:1042:57
#24 0x0000562f913c3e5c clang::Parser::ParseDeclarationOrFunctionDefinition(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*, clang::AccessSpecifier) /home/matt/3c/clang/lib/Parse/Parser.cpp:1154:57
#25 0x0000562f913c4b12 clang::Parser::ParseExternalDeclaration(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) (.localalias) /home/matt/3c/clang/lib/Parse/Parser.cpp:956:58
#26 0x0000562f913c4e15 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool) /home/matt/3c/clang/lib/Parse/Parser.cpp:704:42
#27 0x0000562f913bac6f clang::ParseAST(clang::Sema&, bool, bool) /home/matt/3c/clang/lib/Parse/ParseAST.cpp:157:56
#28 0x0000562f8fd444d5 clang::ASTFrontendAction::ExecuteAction() /home/matt/3c/clang/lib/Frontend/FrontendAction.cpp:1059:1
#29 0x0000562f8fe4eb68 clang::CodeGenAction::ExecuteAction() /home/matt/3c/clang/lib/CodeGen/CodeGenAction.cpp:1185:1
#30 0x0000562f8fd46e7a clang::FrontendAction::Execute() /home/matt/3c/clang/lib/Frontend/FrontendAction.cpp:950:21
#31 0x0000562f8fc870bd llvm::Error::setChecked(bool) /home/matt/3c/llvm/include/llvm/Support/Error.h:305:22
#32 0x0000562f8fc870bd llvm::Error::operator bool() /home/matt/3c/llvm/include/llvm/Support/Error.h:236:15
#33 0x0000562f8fc870bd clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) /home/matt/3c/clang/lib/Frontend/CompilerInstance.cpp:984:42
#34 0x0000562f8fe442be clang::ExecuteCompilerInvocation(clang::CompilerInstance*) /home/matt/3c/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:278:38
#35 0x0000562f8d7fc0a8 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) /home/matt/3c/clang/tools/driver/cc1_main.cpp:240:40
#36 0x0000562f8d7f6105 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) /home/matt/3c/clang/tools/driver/driver.cpp:330:20
#37 0x0000562f8fab52ed operator() /home/matt/3c/clang/lib/Driver/Job.cpp:400:32
#38 0x0000562f8fab52ed 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) /home/matt/3c/llvm/include/llvm/ADT/STLExtras.h:185:52
#39 0x0000562f8eed23c2 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) /home/matt/3c/llvm/lib/Support/CrashRecoveryContext.cpp:419:10
#40 0x0000562f8fab8757 clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, bool*) const /home/matt/3c/clang/lib/Driver/Job.cpp:400:3
#41 0x0000562f8fa7f8eb clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&) const /home/matt/3c/clang/lib/Driver/Compilation.cpp:195:22
#42 0x0000562f8fa804a2 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*> >&) const /home/matt/3c/clang/lib/Driver/Compilation.cpp:246:5
#43 0x0000562f8fa8acc0 llvm::SmallVectorBase<unsigned int>::empty() const /home/matt/3c/llvm/include/llvm/ADT/SmallVector.h:69:47
#44 0x0000562f8fa8acc0 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*> >&) /home/matt/3c/clang/lib/Driver/Driver.cpp:1509:28
#45 0x0000562f8d7f9403 main /home/matt/3c/clang/tools/driver/driver.cpp:502:39
#46 0x00007f6708ce60b3 __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:342:3
#47 0x0000562f8d7f5b7e _start (/home/matt/3c/build/bin/clang+0x2adbb7e)
clang-11: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 11.0.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/matt/3c/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/casts-compiler-crash-28c8f0.c
clang-11: note: diagnostic msg: /tmp/casts-compiler-crash-28c8f0.sh
clang-11: note: diagnostic msg: 

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

I think the proper fix is probably just to add the missing null check. But I don't want to spend the time right now to submit this as a PR and fulfill the related responsibilities (testing, etc.), and even if I did, I don't know if you'd want to spend the time to review the PR now. So I'll just file an issue.