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author | Mandeep Singh Grang <mgrang@codeaurora.org> | 2017-09-06 20:19:10 +0000 |
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committer | Mandeep Singh Grang <mgrang@codeaurora.org> | 2017-09-06 20:19:10 +0000 |
commit | 41915c0baa768b67f4d042e0e3a2868666e79487 (patch) | |
tree | d4aec5f9e3118057a86b04b8c4959f1418f325d0 /docs | |
parent | 9ca441aa442dd8c33b7a580447ede231b8f02ea7 (diff) | |
download | llvm-41915c0baa768b67f4d042e0e3a2868666e79487.tar.gz |
[docs] Add a note on iteration of unordered containers to coding standards
Summary: Beware of non-determinism due to ordering of pointers
Reviewers: dblaikie, dexonsmith
Reviewed By: dblaikie
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D37525
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312667 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
-rw-r--r-- | docs/CodingStandards.rst | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/docs/CodingStandards.rst b/docs/CodingStandards.rst index c4e25e4216e..0de2fc6b1a8 100644 --- a/docs/CodingStandards.rst +++ b/docs/CodingStandards.rst @@ -811,6 +811,21 @@ As a rule of thumb, use ``auto &`` unless you need to copy the result, and use for (const auto *Ptr : Container) { observe(*Ptr); } for (auto *Ptr : Container) { Ptr->change(); } +Beware of non-determinism due to ordering of pointers +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In general, there is no relative ordering among pointers. As a result, +when unordered containers like sets and maps are used with pointer keys +the iteration order is undefined. Hence, iterating such containers may +result in non-deterministic code generation. While the generated code +might not necessarily be "wrong code", this non-determinism might result +in unexpected runtime crashes or simply hard to reproduce bugs on the +customer side making it harder to debug and fix. + +As a rule of thumb, in case an ordered result is expected, remember to +sort an unordered container before iteration. Or use ordered containers +like vector/MapVector/SetVector if you want to iterate pointer keys. + Style Issues ============ |