// The zero Map is empty and ready for use. A Map must not be copied after first use.
//
// In the terminology of [the Go memory model], Map arranges that a write operation
// “synchronizes before” any read operation that observes the effect of the write, where
// read and write operations are defined as follows.
// [Map.Load], [Map.LoadAndDelete], [Map.LoadOrStore], [Map.Swap], [Map.CompareAndSwap],
// and [Map.CompareAndDelete] are read operations;

// Shardz returns a full deep copy of the global map of shards. This should be used only for testing
// and debugging, as the cloning is expensive.
func (e *EndpointIndex) Shardz() map[string]map[string]*EndpointShards {
	e.mu.RLock()
	defer e.mu.RUnlock()
	out := make(map[string]map[string]*EndpointShards, len(e.shardsBySvc))
	for svcKey, v := range e.shardsBySvc {
		out[svcKey] = make(map[string]*EndpointShards, len(v))

			}
			cmap := xdstest.ExtractClusters(clusters)
			got := xdstest.MapKeys(cmap)

			// Check we have all expected clusters
			if !reflect.DeepEqual(xdstest.MapKeys(tt.clusters), got) {
				t.Errorf("expected clusters: %v, got: %v", xdstest.MapKeys(tt.clusters), got)
			}

			for cname, c := range cmap {
				// Check the upstream endpoints match

	// TODO: keep a single varnum map, then make all of these maps slices instead?
	vars map[ir.Node]*ssa.Value

	// fwdVars are variables that are used before they are defined in the current block.
	// This map exists just to coalesce multiple references into a single FwdRef op.
	// *Node is the unique identifier (an ONAME Node) for the variable.
	fwdVars map[ir.Node]*ssa.Value