False positives related to try catch blocks (Value stored to '...' during its initialization is never read)

[llvmbot]

Bugzilla Link	10862
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@tkremenek

Extended Description

Hi,

I am using scan-build (svn from 2011-09-02) to analyze c++ code and get a few false positives related to try catch blocks. My initial attempts to make a small test case did not succeed in replicating the bug. Below are two code snippets for which I get "Value stored to 'status' during its initialization is never read" in a large projet:

---

uint32_t status = info.refStatus;

try {
status = foo();
}
catch(...) {
}

bar(status);

---

int status = this->m_status;
this->m_status = foo();
try {
bar();
}
catch(...) {
this->m_status = status;
}

[llvmbot]

assigned to @tkremenek

[tkremenek]

Hi,

I am using scan-build (svn from 2011-09-02) to analyze c++ code and get a few
false positives related to try catch blocks. My initial attempts to make a
small test case did not succeed in replicating the bug. Below are two code
snippets for which I get "Value stored to 'status' during its initialization is
never read" in a large projet:

---

uint32_t status = info.refStatus;

try {
status = foo();
}
catch(...) {
}

bar(status);

Ah, the warning is not valid here because foo() might throw an exception, correct?

---

---

int status = this->m_status;
this->m_status = foo();
try {
bar();
}
catch(...) {
this->m_status = status;
}

And the warning is clearly bogus here because 'status' is read in the @​catch.

[llvmbot]

---

uint32_t status = info.refStatus;

try {
status = foo();
}
catch(...) {
}

bar(status);

Ah, the warning is not valid here because foo() might throw an exception,
correct?

Indeed.

---

int status = this->m_status;
this->m_status = foo();
try {
bar();
}
catch(...) {
this->m_status = status;
}

And the warning is clearly bogus here because 'status' is read in the @​catch.

Yes

[llvmbot]

test case file
Attached is a small tests case that illustrates the bug.

[llvmbot]

I stumbled about the exact same issue as Tom's first example in clang 3.7.0 on Arch Linux amd64.

The code in my case is https://github.com/xoreos/xoreos-tools/blob/master/src/aurora/gff4file.cpp#L752

I.e.

---

const size_t offset = data.pos();

try {
return Common::readStringFixed(data, encoding, size);
} catch (...) {
}

return Common::UString::format("GFF4: Invalid string encoding (0x%08X)", (uint) offset);

offset is clearly read, but the try-catch block...throws it for a loop.