false positive on optional<string> usage

[llvmbot]

Bugzilla Link	39144
Version	7.0
OS	Linux
Attachments	Code as described in the bug
Reporter	LLVM Bugzilla Contributor
CC	@JonasToth,@haoNoQ

Extended Description

clang-tidy 7.0.0, using GCC 7.2.0 libstdc++

The following code:

--cut-here--

include

include

std::optional makeResponse(); void func(const char *, size_t);

void test() { auto response = makeResponse(); if (!response) return; func(response->c_str(), response->length()); } --end-cut-here

when compiled with clang-tidy 7.0.0 using a compilation like:

--cut [ { "directory": "/home/mattgodbolt/dev/clang-tidy-bug", "command": "/usr/bin/g++ -std=gnu++1z -c repro.cc -o repro.o", "file": "/home/mattgodbolt/dev/clang-tidy-bug/repro.cc" } ] --end-cut

Yields the following apparently bogus error:

~/clang-7.0.0/bin/clang-tidy repro.cc

1 warning generated. repro.cc:10:3: warning: Use of memory after it is freed [clang-analyzer-cplusplus.NewDelete] func(response->c_str(), response->length()); ^ repro.cc:9:7: note: Assuming the condition is false if (!response) return; ^ repro.cc:9:3: note: Taking false branch if (!response) return; ^ repro.cc:10:8: note: Dangling inner pointer obtained here func(response->c_str(), response->length()); ^ repro.cc:10:27: note: Calling 'optional::operator->' func(response->c_str(), response->length()); ^ /usr/bin/../lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/c++/7.3.0/optional:697:16: note: Inner pointer invalidated by call to 'addressof' { return std::addressof(this->_M_get()); } ^ repro.cc:10:27: note: Returning; memory was released func(response->c_str(), response->length()); ^ repro.cc:10:3: note: Use of memory after it is freed func(response->c_str(), response->length()); ^

[haoNoQ]

Hmm, right, std::addressof() does take the object by a non-const reference, but it certainly doesn't invalidate the object's contents.

[JonasToth]

Hi Matt,

thank you for reporting the bug. Because this comes from the Static Analyzer and not clang-tidy (as it only calls the CSA) I moved this bug to the other component.

Best Jonas

[llvmbot]

Correction: I'm using GCC 7.3.0 libstdc++

[llvmbot]

assigned to @rnkovacs