126 lines
3.0 KiB
Go
126 lines
3.0 KiB
Go
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// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package pointer
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// This file implements renumbering, a pre-solver optimization to
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// improve the efficiency of the solver's points-to set representation.
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//
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// TODO(adonovan): rename file "renumber.go"
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import "fmt"
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// renumber permutes a.nodes so that all nodes within an addressable
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// object appear before all non-addressable nodes, maintaining the
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// order of nodes within the same object (as required by offsetAddr).
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//
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// renumber must update every nodeid in the analysis (constraints,
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// Pointers, callgraph, etc) to reflect the new ordering.
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//
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// This is an optimisation to increase the locality and efficiency of
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// sparse representations of points-to sets. (Typically only about
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// 20% of nodes are within an object.)
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//
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// NB: nodes added during solving (e.g. for reflection, SetFinalizer)
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// will be appended to the end.
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//
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// Renumbering makes the PTA log inscrutable. To aid debugging, later
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// phases (e.g. HVN) must not rely on it having occurred.
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//
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func (a *analysis) renumber() {
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if a.log != nil {
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fmt.Fprintf(a.log, "\n\n==== Renumbering\n\n")
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}
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N := nodeid(len(a.nodes))
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newNodes := make([]*node, N, N)
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renumbering := make([]nodeid, N, N) // maps old to new
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var i, j nodeid
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// The zero node is special.
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newNodes[j] = a.nodes[i]
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renumbering[i] = j
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i++
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j++
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// Pass 1: object nodes.
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for i < N {
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obj := a.nodes[i].obj
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if obj == nil {
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i++
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continue
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}
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end := i + nodeid(obj.size)
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for i < end {
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newNodes[j] = a.nodes[i]
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renumbering[i] = j
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i++
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j++
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}
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}
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nobj := j
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// Pass 2: non-object nodes.
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for i = 1; i < N; {
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obj := a.nodes[i].obj
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if obj != nil {
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i += nodeid(obj.size)
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continue
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}
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newNodes[j] = a.nodes[i]
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renumbering[i] = j
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i++
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j++
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}
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if j != N {
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panic(fmt.Sprintf("internal error: j=%d, N=%d", j, N))
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}
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// Log the remapping table.
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if a.log != nil {
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fmt.Fprintf(a.log, "Renumbering nodes to improve density:\n")
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fmt.Fprintf(a.log, "(%d object nodes of %d total)\n", nobj, N)
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for old, new := range renumbering {
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fmt.Fprintf(a.log, "\tn%d -> n%d\n", old, new)
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}
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}
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// Now renumber all existing nodeids to use the new node permutation.
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// It is critical that all reachable nodeids are accounted for!
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// Renumber nodeids in queried Pointers.
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for v, ptr := range a.result.Queries {
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ptr.n = renumbering[ptr.n]
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a.result.Queries[v] = ptr
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}
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for v, ptr := range a.result.IndirectQueries {
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ptr.n = renumbering[ptr.n]
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a.result.IndirectQueries[v] = ptr
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}
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// Renumber nodeids in global objects.
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for v, id := range a.globalobj {
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a.globalobj[v] = renumbering[id]
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}
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// Renumber nodeids in constraints.
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for _, c := range a.constraints {
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c.renumber(renumbering)
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}
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// Renumber nodeids in the call graph.
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for _, cgn := range a.cgnodes {
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cgn.obj = renumbering[cgn.obj]
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for _, site := range cgn.sites {
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site.targets = renumbering[site.targets]
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}
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}
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a.nodes = newNodes
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}
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