[llvm-bugs] [Bug 33137] New: False positive on variable value

via llvm-bugs llvm-bugs at lists.llvm.org
Tue May 23 03:36:02 PDT 2017


            Bug ID: 33137
           Summary: False positive on variable value
           Product: clang
           Version: 4.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Static Analyzer
          Assignee: kremenek at apple.com
          Reporter: natale.patriciello at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 18493
  --> https://bugs.llvm.org/attachment.cgi?id=18493&action=edit
The false positive report

In the source generated by the asn1c compiler, there is the function
der_write_tags. In this, the point 6 is (Assuming 'i' is >= 'tags_count'),
where i is 1. It means that tags_count < 1 (tags_count is an int).

Then, at line 140, there is this cycle:
140             for(i = tags_count - 1; i >= 0; --i) {

where the line (Assuming 'i' is >= 0) is printed two times. Giving the previous
assumption, this is clearly impossible.

I tried to make a small example, but I've failed; it seems that in simple
functions this is well understood by the analyzer.

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