https://bugs.llvm.org/show_bug.cgi?id=36685
Bug ID: 36685
Summary: Possible false positive: takes branches that
contradict each other
Product: clang
Version: 6.0
Hardware: Other
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Static Analyzer
Assignee: dcough...@apple.com
Reporter: manuelm...@gmail.com
CC: llvm-bugs@lists.llvm.org
Created attachment 20048
--> https://bugs.llvm.org/attachment.cgi?id=20048&action=edit
Source code of median search and reduced caller.
The attached reduced source code implements a fast median computation according
to [1] and contains a placeholder caller.
If the caller passes its input array directly, clang does not report any
problems.
If the caller copies its input array to a local array and then runs the median
computation (compile with "-DCOPY"), clang finds a bug.
I therefore suspect a false positive.
The path it takes assumes the following conditions:
Lines 38--40:
array[1] <= array[2]
array[0] <= array[2]
array[1] <= array[0]
Line 43:
Swapping is a NOP due to middle == low + 1.
Lines 50:
array[0] > array[2]
This contradicts assumption array[0] <= array[2], hence the reported bug should
be impossible and thus a false positive.
[1] http://ndevilla.free.fr/median/median.pdf
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