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From: "geoffreydgr at icloud dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug analyzer/109292] New: GCC Static Analyzer NPD false negative because it does not know a simple iterator of `for` loop Date: Mon, 27 Mar 2023 08:53:03 +0000 [thread overview] Message-ID: <bug-109292-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109292 Bug ID: 109292 Summary: GCC Static Analyzer NPD false negative because it does not know a simple iterator of `for` loop Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: analyzer Assignee: dmalcolm at gcc dot gnu.org Reporter: geoffreydgr at icloud dot com Target Milestone: --- GCC Static Analyzer has a NPD false negative about `*c = 0;`(line 20). It seems that GSA does not know the value of the simple iterator `d` of `for` loop. If i change the for statement to if statement with the same semantics, there is no false negative about NPD. See it live: https://godbolt.org/z/PGdbb6osj See it live: https://godbolt.org/z/n61zPPxd7 Input ```c extern void __analyzer_eval(); extern void __analyzer_dump_path(); int a() { int d; for (d = -1; d; ++d) { ; } __analyzer_dump_path(); return d; } int b() { int t = a(); int *c = (void *)t; __analyzer_eval(c == 0); *c = 0; } int main() { b(); } ``` Output: ``` <source>: In function 'b': <source>:18:14: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast] 18 | int *c = (void *)t; | ^ <source>:19:5: warning: UNKNOWN 19 | __analyzer_eval(c == 0); | ^~~~~~~~~~~~~~~~~~~~~~~ <source>:19:5: warning: UNKNOWN <source>: In function 'a': <source>:11:5: note: path 11 | __analyzer_dump_path(); | ^~~~~~~~~~~~~~~~~~~~~~ 'a': events 1-3 | | 7 | for (d = -1; d; ++d) | | ^ ~~~ | | | | | | | (2) ...to here | | (1) following 'true' branch (when 'd != 0')... |...... | 11 | __analyzer_dump_path(); | | ~~~~~~~~~~~~~~~~~~~~~~ | | | | | (3) here | Compiler returned: 0 ```
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