[clang-tidy] bugprone-infinite-loop: detects clearly finite loops as infinite

[def-]

Bugzilla Link	44618
Resolution	FIXED
Resolved on	Jan 29, 2020 13:02
Version	unspecified
OS	Linux
Blocks	#43900
CC	@EugeneZelenko,@zmodem
Fixed by commit(s)	rG70f4c6e7b14f225f9628fbdab3620ce037613351

Extended Description

Hi,

The new bugprone-infinite-loop check is not detecting some easy patterns of finite loops, thus leading to false positives. Not sure if this can easily be fixed:

$ clang-tidy --version
LLVM (http://llvm.org/):
LLVM version 10.0.175git
Optimized build.
Default target: x86_64-unknown-linux-gnu
Host CPU: broadwell
$ cat .clang-tidy
Checks: bugprone-infinite-loop
$ cat x.cpp
#include

int main(int /argc/, char** /argv/)
{
char foobar[] = "foobar";
char *pattern = foobar;
while (char c = *pattern) {
if (c == 'o') {
std::cout << "o" << std::endl;
}

    ++pattern;
}

return 0;

}
$ clang-tidy x.cpp
/home/d067158/x.cpp:7:5: warning: this loop is infinite; none of its condition variables (c) are updated in the loop body [clang-tidy-bugprone-infinite-loop]
while (char c = *pattern) {
^
$ ./x
o
o

Best regards
Dennis

[llvmbot]

Reduced test case:

void false_positive() {
int n = 10;
while (int m = n) {
--n;
}
}

However, no false positive for this:

void no_false_positive() {
int n = 10, m;
while (m = n) {
--n;
}
}

[llvmbot]

Fix uploaded for review: https://reviews.llvm.org/D73270

[zmodem]

Fix uploaded for review: https://reviews.llvm.org/D73270

That was committed, and later cherry-picked to 10.x in d275de3