// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package symbols

// This file is a subset of golang.org/x/vuln/internal/vulncheck/slicing.go.

import (
	"golang.org/x/tools/go/callgraph"
	"golang.org/x/tools/go/ssa"
)

// forwardSlice computes the transitive closure of functions forward reachable
// via calls in cg or referred to in an instruction starting from `sources`.
func forwardSlice(sources map[*ssa.Function]bool, cg *callgraph.Graph) map[*ssa.Function]bool {
	seen := make(map[*ssa.Function]bool)
	var visit func(f *ssa.Function)
	visit = func(f *ssa.Function) {
		if seen[f] {
			return
		}
		seen[f] = true

		if n := cg.Nodes[f]; n != nil {
			for _, e := range n.Out {
				if e.Site != nil {
					visit(e.Callee.Func)
				}
			}
		}

		var buf [10]*ssa.Value // avoid alloc in common case
		for _, b := range f.Blocks {
			for _, instr := range b.Instrs {
				for _, op := range instr.Operands(buf[:0]) {
					if fn, ok := (*op).(*ssa.Function); ok {
						visit(fn)
					}
				}
			}
		}
	}
	for source := range sources {
		visit(source)
	}
	return seen
}

// pruneSet removes functions in `set` that are in `toPrune`.
func pruneSet(set, toPrune map[*ssa.Function]bool) {
	for f := range set {
		if !toPrune[f] {
			delete(set, f)
		}
	}
}