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-rw-r--r--src/cmd/compile/internal/ssa/stackalloc.go420
1 files changed, 420 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/stackalloc.go b/src/cmd/compile/internal/ssa/stackalloc.go
new file mode 100644
index 0000000..406a3c3
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/stackalloc.go
@@ -0,0 +1,420 @@
+// Copyright 2015 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.
+
+// TODO: live at start of block instead?
+
+package ssa
+
+import (
+ "cmd/compile/internal/types"
+ "cmd/internal/src"
+ "fmt"
+)
+
+type stackAllocState struct {
+ f *Func
+
+ // live is the output of stackalloc.
+ // live[b.id] = live values at the end of block b.
+ live [][]ID
+
+ // The following slices are reused across multiple users
+ // of stackAllocState.
+ values []stackValState
+ interfere [][]ID // interfere[v.id] = values that interfere with v.
+ names []LocalSlot
+ slots []int
+ used []bool
+
+ nArgSlot, // Number of Values sourced to arg slot
+ nNotNeed, // Number of Values not needing a stack slot
+ nNamedSlot, // Number of Values using a named stack slot
+ nReuse, // Number of values reusing a stack slot
+ nAuto, // Number of autos allocated for stack slots.
+ nSelfInterfere int32 // Number of self-interferences
+}
+
+func newStackAllocState(f *Func) *stackAllocState {
+ s := f.Cache.stackAllocState
+ if s == nil {
+ return new(stackAllocState)
+ }
+ if s.f != nil {
+ f.fe.Fatalf(src.NoXPos, "newStackAllocState called without previous free")
+ }
+ return s
+}
+
+func putStackAllocState(s *stackAllocState) {
+ for i := range s.values {
+ s.values[i] = stackValState{}
+ }
+ for i := range s.interfere {
+ s.interfere[i] = nil
+ }
+ for i := range s.names {
+ s.names[i] = LocalSlot{}
+ }
+ for i := range s.slots {
+ s.slots[i] = 0
+ }
+ for i := range s.used {
+ s.used[i] = false
+ }
+ s.f.Cache.stackAllocState = s
+ s.f = nil
+ s.live = nil
+ s.nArgSlot, s.nNotNeed, s.nNamedSlot, s.nReuse, s.nAuto, s.nSelfInterfere = 0, 0, 0, 0, 0, 0
+}
+
+type stackValState struct {
+ typ *types.Type
+ spill *Value
+ needSlot bool
+ isArg bool
+}
+
+// stackalloc allocates storage in the stack frame for
+// all Values that did not get a register.
+// Returns a map from block ID to the stack values live at the end of that block.
+func stackalloc(f *Func, spillLive [][]ID) [][]ID {
+ if f.pass.debug > stackDebug {
+ fmt.Println("before stackalloc")
+ fmt.Println(f.String())
+ }
+ s := newStackAllocState(f)
+ s.init(f, spillLive)
+ defer putStackAllocState(s)
+
+ s.stackalloc()
+ if f.pass.stats > 0 {
+ f.LogStat("stack_alloc_stats",
+ s.nArgSlot, "arg_slots", s.nNotNeed, "slot_not_needed",
+ s.nNamedSlot, "named_slots", s.nAuto, "auto_slots",
+ s.nReuse, "reused_slots", s.nSelfInterfere, "self_interfering")
+ }
+
+ return s.live
+}
+
+func (s *stackAllocState) init(f *Func, spillLive [][]ID) {
+ s.f = f
+
+ // Initialize value information.
+ if n := f.NumValues(); cap(s.values) >= n {
+ s.values = s.values[:n]
+ } else {
+ s.values = make([]stackValState, n)
+ }
+ for _, b := range f.Blocks {
+ for _, v := range b.Values {
+ s.values[v.ID].typ = v.Type
+ s.values[v.ID].needSlot = !v.Type.IsMemory() && !v.Type.IsVoid() && !v.Type.IsFlags() && f.getHome(v.ID) == nil && !v.rematerializeable() && !v.OnWasmStack
+ s.values[v.ID].isArg = v.Op == OpArg
+ if f.pass.debug > stackDebug && s.values[v.ID].needSlot {
+ fmt.Printf("%s needs a stack slot\n", v)
+ }
+ if v.Op == OpStoreReg {
+ s.values[v.Args[0].ID].spill = v
+ }
+ }
+ }
+
+ // Compute liveness info for values needing a slot.
+ s.computeLive(spillLive)
+
+ // Build interference graph among values needing a slot.
+ s.buildInterferenceGraph()
+}
+
+func (s *stackAllocState) stackalloc() {
+ f := s.f
+
+ // Build map from values to their names, if any.
+ // A value may be associated with more than one name (e.g. after
+ // the assignment i=j). This step picks one name per value arbitrarily.
+ if n := f.NumValues(); cap(s.names) >= n {
+ s.names = s.names[:n]
+ } else {
+ s.names = make([]LocalSlot, n)
+ }
+ names := s.names
+ for _, name := range f.Names {
+ // Note: not "range f.NamedValues" above, because
+ // that would be nondeterministic.
+ for _, v := range f.NamedValues[name] {
+ names[v.ID] = name
+ }
+ }
+
+ // Allocate args to their assigned locations.
+ for _, v := range f.Entry.Values {
+ if v.Op != OpArg {
+ continue
+ }
+ if v.Aux == nil {
+ f.Fatalf("%s has nil Aux\n", v.LongString())
+ }
+ loc := LocalSlot{N: v.Aux.(GCNode), Type: v.Type, Off: v.AuxInt}
+ if f.pass.debug > stackDebug {
+ fmt.Printf("stackalloc %s to %s\n", v, loc)
+ }
+ f.setHome(v, loc)
+ }
+
+ // For each type, we keep track of all the stack slots we
+ // have allocated for that type.
+ // TODO: share slots among equivalent types. We would need to
+ // only share among types with the same GC signature. See the
+ // type.Equal calls below for where this matters.
+ locations := map[*types.Type][]LocalSlot{}
+
+ // Each time we assign a stack slot to a value v, we remember
+ // the slot we used via an index into locations[v.Type].
+ slots := s.slots
+ if n := f.NumValues(); cap(slots) >= n {
+ slots = slots[:n]
+ } else {
+ slots = make([]int, n)
+ s.slots = slots
+ }
+ for i := range slots {
+ slots[i] = -1
+ }
+
+ // Pick a stack slot for each value needing one.
+ var used []bool
+ if n := f.NumValues(); cap(s.used) >= n {
+ used = s.used[:n]
+ } else {
+ used = make([]bool, n)
+ s.used = used
+ }
+ for _, b := range f.Blocks {
+ for _, v := range b.Values {
+ if !s.values[v.ID].needSlot {
+ s.nNotNeed++
+ continue
+ }
+ if v.Op == OpArg {
+ s.nArgSlot++
+ continue // already picked
+ }
+
+ // If this is a named value, try to use the name as
+ // the spill location.
+ var name LocalSlot
+ if v.Op == OpStoreReg {
+ name = names[v.Args[0].ID]
+ } else {
+ name = names[v.ID]
+ }
+ if name.N != nil && v.Type.Compare(name.Type) == types.CMPeq {
+ for _, id := range s.interfere[v.ID] {
+ h := f.getHome(id)
+ if h != nil && h.(LocalSlot).N == name.N && h.(LocalSlot).Off == name.Off {
+ // A variable can interfere with itself.
+ // It is rare, but it can happen.
+ s.nSelfInterfere++
+ goto noname
+ }
+ }
+ if f.pass.debug > stackDebug {
+ fmt.Printf("stackalloc %s to %s\n", v, name)
+ }
+ s.nNamedSlot++
+ f.setHome(v, name)
+ continue
+ }
+
+ noname:
+ // Set of stack slots we could reuse.
+ locs := locations[v.Type]
+ // Mark all positions in locs used by interfering values.
+ for i := 0; i < len(locs); i++ {
+ used[i] = false
+ }
+ for _, xid := range s.interfere[v.ID] {
+ slot := slots[xid]
+ if slot >= 0 {
+ used[slot] = true
+ }
+ }
+ // Find an unused stack slot.
+ var i int
+ for i = 0; i < len(locs); i++ {
+ if !used[i] {
+ s.nReuse++
+ break
+ }
+ }
+ // If there is no unused stack slot, allocate a new one.
+ if i == len(locs) {
+ s.nAuto++
+ locs = append(locs, LocalSlot{N: f.fe.Auto(v.Pos, v.Type), Type: v.Type, Off: 0})
+ locations[v.Type] = locs
+ }
+ // Use the stack variable at that index for v.
+ loc := locs[i]
+ if f.pass.debug > stackDebug {
+ fmt.Printf("stackalloc %s to %s\n", v, loc)
+ }
+ f.setHome(v, loc)
+ slots[v.ID] = i
+ }
+ }
+}
+
+// computeLive computes a map from block ID to a list of
+// stack-slot-needing value IDs live at the end of that block.
+// TODO: this could be quadratic if lots of variables are live across lots of
+// basic blocks. Figure out a way to make this function (or, more precisely, the user
+// of this function) require only linear size & time.
+func (s *stackAllocState) computeLive(spillLive [][]ID) {
+ s.live = make([][]ID, s.f.NumBlocks())
+ var phis []*Value
+ live := s.f.newSparseSet(s.f.NumValues())
+ defer s.f.retSparseSet(live)
+ t := s.f.newSparseSet(s.f.NumValues())
+ defer s.f.retSparseSet(t)
+
+ // Instead of iterating over f.Blocks, iterate over their postordering.
+ // Liveness information flows backward, so starting at the end
+ // increases the probability that we will stabilize quickly.
+ po := s.f.postorder()
+ for {
+ changed := false
+ for _, b := range po {
+ // Start with known live values at the end of the block
+ live.clear()
+ live.addAll(s.live[b.ID])
+
+ // Propagate backwards to the start of the block
+ phis = phis[:0]
+ for i := len(b.Values) - 1; i >= 0; i-- {
+ v := b.Values[i]
+ live.remove(v.ID)
+ if v.Op == OpPhi {
+ // Save phi for later.
+ // Note: its args might need a stack slot even though
+ // the phi itself doesn't. So don't use needSlot.
+ if !v.Type.IsMemory() && !v.Type.IsVoid() {
+ phis = append(phis, v)
+ }
+ continue
+ }
+ for _, a := range v.Args {
+ if s.values[a.ID].needSlot {
+ live.add(a.ID)
+ }
+ }
+ }
+
+ // for each predecessor of b, expand its list of live-at-end values
+ // invariant: s contains the values live at the start of b (excluding phi inputs)
+ for i, e := range b.Preds {
+ p := e.b
+ t.clear()
+ t.addAll(s.live[p.ID])
+ t.addAll(live.contents())
+ t.addAll(spillLive[p.ID])
+ for _, v := range phis {
+ a := v.Args[i]
+ if s.values[a.ID].needSlot {
+ t.add(a.ID)
+ }
+ if spill := s.values[a.ID].spill; spill != nil {
+ //TODO: remove? Subsumed by SpillUse?
+ t.add(spill.ID)
+ }
+ }
+ if t.size() == len(s.live[p.ID]) {
+ continue
+ }
+ // grow p's live set
+ s.live[p.ID] = append(s.live[p.ID][:0], t.contents()...)
+ changed = true
+ }
+ }
+
+ if !changed {
+ break
+ }
+ }
+ if s.f.pass.debug > stackDebug {
+ for _, b := range s.f.Blocks {
+ fmt.Printf("stacklive %s %v\n", b, s.live[b.ID])
+ }
+ }
+}
+
+func (f *Func) getHome(vid ID) Location {
+ if int(vid) >= len(f.RegAlloc) {
+ return nil
+ }
+ return f.RegAlloc[vid]
+}
+
+func (f *Func) setHome(v *Value, loc Location) {
+ for v.ID >= ID(len(f.RegAlloc)) {
+ f.RegAlloc = append(f.RegAlloc, nil)
+ }
+ f.RegAlloc[v.ID] = loc
+}
+
+func (s *stackAllocState) buildInterferenceGraph() {
+ f := s.f
+ if n := f.NumValues(); cap(s.interfere) >= n {
+ s.interfere = s.interfere[:n]
+ } else {
+ s.interfere = make([][]ID, n)
+ }
+ live := f.newSparseSet(f.NumValues())
+ defer f.retSparseSet(live)
+ for _, b := range f.Blocks {
+ // Propagate liveness backwards to the start of the block.
+ // Two values interfere if one is defined while the other is live.
+ live.clear()
+ live.addAll(s.live[b.ID])
+ for i := len(b.Values) - 1; i >= 0; i-- {
+ v := b.Values[i]
+ if s.values[v.ID].needSlot {
+ live.remove(v.ID)
+ for _, id := range live.contents() {
+ // Note: args can have different types and still interfere
+ // (with each other or with other values). See issue 23522.
+ if s.values[v.ID].typ.Compare(s.values[id].typ) == types.CMPeq || v.Op == OpArg || s.values[id].isArg {
+ s.interfere[v.ID] = append(s.interfere[v.ID], id)
+ s.interfere[id] = append(s.interfere[id], v.ID)
+ }
+ }
+ }
+ for _, a := range v.Args {
+ if s.values[a.ID].needSlot {
+ live.add(a.ID)
+ }
+ }
+ if v.Op == OpArg && s.values[v.ID].needSlot {
+ // OpArg is an input argument which is pre-spilled.
+ // We add back v.ID here because we want this value
+ // to appear live even before this point. Being live
+ // all the way to the start of the entry block prevents other
+ // values from being allocated to the same slot and clobbering
+ // the input value before we have a chance to load it.
+ live.add(v.ID)
+ }
+ }
+ }
+ if f.pass.debug > stackDebug {
+ for vid, i := range s.interfere {
+ if len(i) > 0 {
+ fmt.Printf("v%d interferes with", vid)
+ for _, x := range i {
+ fmt.Printf(" v%d", x)
+ }
+ fmt.Println()
+ }
+ }
+ }
+}
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