63 lines
1.1 KiB
Go
63 lines
1.1 KiB
Go
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package pass
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import (
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"github.com/mmcloughlin/avo"
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"github.com/mmcloughlin/avo/reg"
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)
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// Liveness computes register liveness.
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func Liveness(fn *avo.Function) error {
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is := fn.Instructions()
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// Initialize to empty sets.
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for _, i := range is {
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i.LiveIn = map[reg.ID]bool{}
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i.LiveOut = map[reg.ID]bool{}
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}
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// Iterative dataflow analysis.
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for {
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changes := false
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for _, i := range is {
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// in[n] = use[n] UNION (out[n] - def[n])
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nin := len(i.LiveIn)
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for _, r := range i.InputRegisters() {
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i.LiveIn[r.ID()] = true
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}
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def := map[reg.ID]bool{}
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for _, r := range i.OutputRegisters() {
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def[r.ID()] = true
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}
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for id := range i.LiveOut {
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if !def[id] {
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i.LiveIn[id] = true
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}
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}
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if len(i.LiveIn) != nin {
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changes = true
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}
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// out[n] = UNION[s IN succ[n]] in[s]
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nout := len(i.LiveOut)
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for _, s := range i.Succ {
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if s == nil {
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continue
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}
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for id := range s.LiveIn {
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i.LiveOut[id] = true
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}
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}
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if len(i.LiveOut) != nout {
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changes = true
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}
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}
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if !changes {
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break
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}
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}
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return nil
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}
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