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Input edges (use-def) express data flow dependencies, used for scheduling.
Non-reducible loops are not supported with the LoopBegin/LoopEnd design.
Phi nodes are tied to merge nodes:
class PhiNode extends Node {
...
MergeNode merge()
ValueNode valueAt(EndNode pred)
}
While building the graph, we create floating nodes for all nodes where this does not require any special analysis or dependency creation. Some operations that cannot immediately be represented as floating nodes, such as memory read operations, are transformed into floating nodes by later optimization phases that insert the appropriate dependencies.
[…] this representation simplifies a number of optimizations by removing the burden of maintaining a valid schedule or performing code motion. Before emitting machine code, the IR is fully scheduled by assigning each node to a block in the control-flow graph and by ordering the nodes inside each block. During scheduling, simple heuristics are used to apply some code motion optimization such as hoisting code out of loops.
Nodes have at most one predecessor.