https://bugs.llvm.org/show_bug.cgi?id=51158
Bug ID: 51158
Summary: Bad warning behavior for empty enums in general and
std::byte in particular
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected],
[email protected]
If an enumeration has no enumerators, it is safe to assume that it can take on
any value of the underlying type and it is being used as a strong typedef not a
list of possible values. A few clang warnings do not take this edge case into
account, which shows up in the standard library because that is how `std::byte`
is implemented.
When compiling the following translation unit with `-Wcovered-switch-default`
```
enum class byte : unsigned char {};
void f(byte b) {
switch (b) {
default: break;
}
}
```
clang warns (incorrectly, in my opinion)
```
<source>:5:3: warning: default label in switch which covers all enumeration
values [-Wcovered-switch-default]
default: break;
^
1 warning generated.
Compiler returned: 0
```
See it live: https://godbolt.org/z/vazPzefxr
When compiling the following translation unit with no additional flags
```
enum class byte : unsigned char {};
void f(byte b) {
switch (b) {
case byte(0x00): break;
}
}
```
clang warns (incorrectly)
```
<source>:5:8: warning: case value not in enumerated type 'byte' [-Wswitch]
case byte(0x00): break;
^
1 warning generated.
Compiler returned: 0
```
See it live: https://godbolt.org/z/bKGoWMev9
It's possible to turn off the warning by changing the code slightly to
```
enum class byte : unsigned char {};
constexpr auto zero = byte(0x00);
void f(byte b) {
switch (b) {
case zero: break;
}
}
```
Although making it a local constexpr variable does not turn off the warning,
which is strange.
Compiling the following translation unit with `-Wmissing-noreturn`
```
enum class byte : unsigned char {};
void f(byte b) {
switch (b) {
}
}
```
causes clang to incorrectly emit
```
<source>:3:16: warning: function 'f' could be declared with attribute
'noreturn' [-Wmissing-noreturn]
void f(byte b) {
^
1 warning generated.
Compiler returned: 0
```
See it live: https://godbolt.org/z/qYY9z75cs
The following translation unit causes clang to crash with an assertion failure
when compiled with `--Weverything -Wno-c++98-compat-pedantic
-Wno-missing-prototypes -Wno-missing-noreturn -Wno-covered-switch-default` (not
sure which warning in particular causes it)
```
enum class byte : unsigned char {};
void f(byte b) {
switch (b) {
default: break;
}
}
```
```
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: /opt/compiler-explorer/clang-trunk/bin/clang++ -g -o
/app/output.s -mllvm --x86-asm-syntax=intel -S
--gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics
-fno-crash-diagnostics -Weverything -Wno-c++98-compat-pedantic
-Wno-missing-prototypes -Wno-missing-noreturn -Wno-covered-switch-default
<source>
1. <eof> parser at end of file
2. <source>:3:16: parsing function body 'f'
#0 0x000055b680a1da3f PrintStackTraceSignalHandler(void*) Signals.cpp:0:0
#1 0x000055b680a1b900 llvm::sys::CleanupOnSignal(unsigned long)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x33da900)
#2 0x000055b68096d2e8 CrashRecoverySignalHandler(int)
CrashRecoveryContext.cpp:0:0
#3 0x00007f3624e143c0 __restore_rt
(/lib/x86_64-linux-gnu/libpthread.so.0+0x153c0)
#4 0x000055b68312a113
clang::consumed::ConsumedAnalyzer::run(clang::AnalysisDeclContext&)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x5ae9113)
#5 0x000055b683054ece
clang::sema::AnalysisBasedWarnings::IssueWarnings(clang::sema::AnalysisBasedWarnings::Policy,
clang::sema::FunctionScopeInfo*, clang::Decl const*, clang::QualType)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x5a13ece)
#6 0x000055b6828cfa63
clang::Sema::PopFunctionScopeInfo(clang::sema::AnalysisBasedWarnings::Policy
const*, clang::Decl const*, clang::QualType)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x528ea63)
#7 0x000055b682a2fd70 clang::Sema::ActOnFinishFunctionBody(clang::Decl*,
clang::Stmt*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x53eed70)
#8 0x000055b68285f377 clang::Parser::ParseFunctionStatementBody(clang::Decl*,
clang::Parser::ParseScope&)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x521e377)
#9 0x000055b6827b94f4
clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&,
clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x51784f4)
#10 0x000055b6827e24a1 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&,
clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x51a14a1)
#11 0x000055b6827b4589
clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributesWithRange&,
clang::ParsingDeclSpec&, clang::AccessSpecifier)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x5173589)
#12 0x000055b6827b4c91
clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributesWithRange&,
clang::ParsingDeclSpec*, clang::AccessSpecifier) (.part.280) Parser.cpp:0:0
#13 0x000055b6827babb9
clang::Parser::ParseExternalDeclaration(clang::ParsedAttributesWithRange&,
clang::ParsingDeclSpec*)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x5179bb9)
#14 0x000055b6827bbfd9
clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x517afd9)
#15 0x000055b6827af839 clang::ParseAST(clang::Sema&, bool, bool)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x516e839)
#16 0x000055b681956b52 clang::CodeGenAction::ExecuteAction()
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x4315b52)
#17 0x000055b68130a901 clang::FrontendAction::Execute()
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x3cc9901)
#18 0x000055b6812a86f2
clang::CompilerInstance::ExecuteAction(clang::FrontendAction&)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x3c676f2)
#19 0x000055b6813d6643
clang::ExecuteCompilerInvocation(clang::CompilerInstance*)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x3d95643)
#20 0x000055b67e7f09ec cc1_main(llvm::ArrayRef<char const*>, char const*,
void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x11af9ec)
#21 0x000055b67e7ecb8d ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&)
driver.cpp:0:0
#22 0x000055b6811557a5 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
#23 0x000055b68096d8d3
llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x332c8d3)
#24 0x000055b68115767e
clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>
>, std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >*, bool*) const
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x3b1667e)
#25 0x000055b68112d37a
clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&,
clang::driver::Command const*&) const
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x3aec37a)
#26 0x000055b68112decf
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+++0x3aececf)
#27 0x000055b681137145
clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&,
llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*> >&)
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x3af6145)
#28 0x000055b67e705d2e main
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x10c4d2e)
#29 0x00007f36248c40b3 __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x270b3)
#30 0x000055b67e7ec70a _start
(/opt/compiler-explorer/clang-trunk/bin/clang+++0x11ab70a)
clang-13: error: clang frontend command failed with exit code 139 (use -v to
see invocation)
Compiler returned: 139
```
See it live: https://godbolt.org/z/G3jYTcobf
All of these in a single file: https://godbolt.org/z/hbGGWa9qW
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
