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| -rw-r--r-- | llvm/docs/CodingStandards.rst | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/llvm/docs/CodingStandards.rst b/llvm/docs/CodingStandards.rst index c4e25e4216e..0de2fc6b1a8 100644 --- a/llvm/docs/CodingStandards.rst +++ b/llvm/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 ============ |
