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docs: [spec] Remove references to causal cone and Order edges from Input #762

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Jan 3, 2024
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docs: [spec] Remove references to causal cone and Order edges from Input #762

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docs: [spec] Remove reference to causal cone
acl-cqc Jan 2, 2024
c59982f
And some more, move statement about topsort, and associated tidies
acl-cqc Jan 2, 2024
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24 changes: 9 additions & 15 deletions specification/hugr.md
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Original file line number Diff line number Diff line change
Expand Up @@ -267,19 +267,13 @@ the following basic dataflow operations are available (in addition to the

- `Input/Output`: input/output nodes, the outputs of `Input` node are
the inputs to the function, and the inputs to `Output` are the
outputs of the function. In a data dependency subgraph, a valid
ordering of operations can be achieved by topologically sorting the
nodes starting from `Input` with respect to the Value and Order
edges.
outputs of the function.
- `Call`: Call a statically defined function. There is an incoming
`Static<Function>` edge to specify the graph being called. The
signature of the node (defined by its incoming and outgoing `Value` edges) matches the function being called.
- `LoadConstant<T>`: has an incoming `Static<T>` edge, where `T` is a `CopyableType`, and a
`Value<Local,T>` output, used to load a static constant into the local
dataflow graph. They also have an incoming `Order` edge connecting
them to the `Input` node, as should all operations that
take no dataflow input, to ensure they lie in the causal cone of the
`Input` node when traversing.
dataflow graph.
- `identity<T>`: pass-through, no operation is performed.
- `DFG`: A nested dataflow graph.
These nodes are parents in the hierarchy.
Expand Down Expand Up @@ -515,10 +509,11 @@ graph:
cycles. The common parent is a CFG-node.

**Dataflow Sibling Graph (DSG)**: nodes are operations, `CFG`,
`Conditional`, `TailLoop` and `DFG` nodes; edges are `Value`, `Order` and `Static`;
and must be acyclic. There is a unique Input node and Output node. All nodes must be
reachable from the Input node, and must reach the Output node. The common parent
may be a `FuncDefn`, `TailLoop`, `DFG`, `Case` or `DFB` node.
`Conditional`, `TailLoop` and `DFG` nodes; edges are `Value`, `Order` and `Static`, and must be acyclic.
(Thus a valid ordering of operations can be achieved by topologically sorting the
nodes.)
There is a unique Input node and Output node.
The common parent may be a `FuncDefn`, `TailLoop`, `DFG`, `Case` or `DFB` node.

| **Edge Kind** | **Locality** |
| -------------- | ------------ |
Expand Down Expand Up @@ -1340,16 +1335,15 @@ remove it. (If there is an non-local edge from `n0` to a descendent of

Given a `Const<T>` node `c`, and optionally `P`, a parent of a DSG, add a new
`LoadConstant<T>` node `n` as a child of `P` with a `Static<T>` edge
from `c` to `n` and no outgoing edges from `n`. Also add an Order edge
from the Input node under `P` to `n`. Return the ID of `n`. If `P` is
from `c` to `n` and no outgoing edges from `n`. Return the ID of `n`. If `P` is
omitted it defaults to the parent of `c` (in this case said `c` will
have to be in a DSG or CSG rather than under the Module Root.) If `P` is
provided, it must be a descendent of the parent of `c`.

###### `RemoveConstIgnore`

Given a `LoadConstant<T>` node `n` that has no outgoing edges, remove
it (and its incoming value and Order edges) from the hugr.
it (and its incoming Static edge and any Order edges) from the hugr.

##### Insertion and removal of const nodes

Expand Down