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[Offload][NFC] Avoid temporary string copies in InfoTreeNode #159372

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Merged
merged 2 commits into from
Sep 23, 2025
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[Offload][NFC] Avoid temporary string copies in InfoTreeNode #159372

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7183afa
[Offload][NFCI] Avoid temporary string copies in InfoTreeNode
AlexeySachkov Sep 17, 2025
663d2e1
Apply comments: made the API non-move-only
AlexeySachkov Sep 18, 2025
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10 changes: 5 additions & 5 deletions offload/plugins-nextgen/common/include/PluginInterface.h
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Original file line number Diff line number Diff line change
Expand Up @@ -192,17 +192,16 @@ struct InfoTreeNode {
llvm::DenseMap<DeviceInfo, size_t> DeviceInfoMap;

InfoTreeNode() : InfoTreeNode("", std::monostate{}, "") {}
InfoTreeNode(std::string Key, VariantType Value, std::string Units)
: Key(Key), Value(Value), Units(Units) {}
InfoTreeNode(std::string &&Key, VariantType Value, std::string &&Units)
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@jhuber6 jhuber6 Sep 17, 2025

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Suggested change
InfoTreeNode(std::string &&Key, VariantType Value, std::string &&Units)
InfoTreeNode(std::string Key, VariantType Value, std::string Units)

I'm pretty sure the typical idiom is to pass-by-value and then move. This should move an r-value into Key and then move it into the member. What you have is technically correct for moving, but makes the interface 'move only' which isn't as great.

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@AlexeySachkov AlexeySachkov Sep 17, 2025

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What you have is technically correct for moving, but makes the interface 'move only' which isn't as great.

Ok, I see. I postponed the std::string construction till the very last moment, but what we could do is to construct it as early as possible and then just move it "internally" since we already operate on a copy and that would make the interface more flexible (i.e. non-'move-only'), right?

Does this apply to the constructor as well, or only to the add method?

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@AlexeySachkov AlexeySachkov Sep 18, 2025

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If I understood it correctly, the concern should be resolved in 663d2e1

: Key(std::move(Key)), Value(Value), Units(std::move(Units)) {}

/// Add a new info entry as a child of this node. The entry requires at least
/// a key string in \p Key. The value in \p Value is optional and can be any
/// type that is representable as a string. The units in \p Units is optional
/// and must be a string. Providing a device info key allows liboffload to
/// use that value for an appropriate olGetDeviceInfo query
template <typename T = std::monostate>
InfoTreeNode *add(std::string Key, T Value = T(),
const std::string &Units = std::string(),
InfoTreeNode *add(std::string &&Key, T Value = T(), std::string &&Units = "",
std::optional<DeviceInfo> DeviceInfoKey = std::nullopt) {
assert(!Key.empty() && "Invalid info key");

Expand All @@ -217,7 +216,8 @@ struct InfoTreeNode {
else
ValueVariant = std::string{Value};

auto Ptr = &Children->emplace_back(Key, ValueVariant, Units);
auto Ptr =
&Children->emplace_back(std::move(Key), ValueVariant, std::move(Units));

if (DeviceInfoKey)
DeviceInfoMap[*DeviceInfoKey] = Children->size() - 1;
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