[llvm-bugs] [Bug 37665] New: False positive: array values filled with over-aligned size are treated as garbage or undefined

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37665

            Bug ID: 37665
           Summary: False positive: array values filled with over-aligned
                    size are treated as garbage or undefined
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Static Analyzer
          Assignee: dcoughlin at apple.com
          Reporter: arseny.kapoulkine at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20386
  --> https://bugs.llvm.org/attachment.cgi?id=20386&action=edit
minimal repro

Given a function, that takes size_t count and fills a local array with count
values and then reads count values from the array, everything works well.

When instead we use the following expression to align count upwards:

size_t aligned_count = (count + 15) & ~15;

And fill aligned_count elements instead, static analyzer thinks that elements
read from the array could be uninitialized. This doesn't seem to be due to
count possibly overflowing since removing "& ~15" removes the error.

Adding assert(aligned_count >= count); doesn't seem to fix this :(

Reproducer online: https://godbolt.org/g/55vJQ6

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20180603/db2600e1/attachment-0001.html>