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path: root/src/cmd/compile/internal/ssa/regalloc.go
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Diffstat (limited to 'src/cmd/compile/internal/ssa/regalloc.go')
-rw-r--r--src/cmd/compile/internal/ssa/regalloc.go456
1 files changed, 456 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/regalloc.go b/src/cmd/compile/internal/ssa/regalloc.go
new file mode 100644
index 0000000000..c798d2e936
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/regalloc.go
@@ -0,0 +1,456 @@
+package ssa
+
+import (
+ "fmt"
+ "log"
+ "sort"
+)
+
+func setloc(home []Location, v *Value, loc Location) []Location {
+ for v.ID >= ID(len(home)) {
+ home = append(home, nil)
+ }
+ home[v.ID] = loc
+ return home
+}
+
+type register uint
+
+// TODO: make arch-dependent
+var numRegs register = 32
+
+var registers = [...]Register{
+ Register{0, "AX"},
+ Register{1, "CX"},
+ Register{2, "DX"},
+ Register{3, "BX"},
+ Register{4, "SP"},
+ Register{5, "BP"},
+ Register{6, "SI"},
+ Register{7, "DI"},
+ Register{8, "R8"},
+ Register{9, "R9"},
+ Register{10, "R10"},
+ Register{11, "R11"},
+ Register{12, "R12"},
+ Register{13, "R13"},
+ Register{14, "R14"},
+ Register{15, "R15"},
+
+ // TODO X0, ...
+ // TODO: make arch-dependent
+ Register{16, "FP"}, // pseudo-register, actually a constant offset from SP
+ Register{17, "FLAGS"},
+ Register{18, "OVERWRITE"},
+}
+
+// countRegs returns the number of set bits in the register mask.
+func countRegs(r regMask) int {
+ n := 0
+ for r != 0 {
+ n += int(r & 1)
+ r >>= 1
+ }
+ return n
+}
+
+// pickReg picks an arbitrary register from the register mask.
+func pickReg(r regMask) register {
+ // pick the lowest one
+ if r == 0 {
+ panic("can't pick a register from an empty set")
+ }
+ for i := register(0); ; i++ {
+ if r&1 != 0 {
+ return i
+ }
+ r >>= 1
+ }
+}
+
+// regalloc performs register allocation on f. It sets f.RegAlloc
+// to the resulting allocation.
+func regalloc(f *Func) {
+ // For now, a very simple allocator. Everything has a home
+ // location on the stack (TBD as a subsequent stackalloc pass).
+ // Values live in the home locations at basic block boundaries.
+ // We use a simple greedy allocator within a basic block.
+ home := make([]Location, f.NumValues())
+
+ addPhiCopies(f) // add copies of phi inputs in preceeding blocks
+
+ // Compute live values at the end of each block.
+ live := live(f)
+ lastUse := make([]int, f.NumValues())
+
+ var oldSched []*Value
+
+ // Hack to find fp, sp Values and assign them a register. (TODO: make not so hacky)
+ var fp, sp *Value
+ for _, v := range f.Entry.Values {
+ switch v.Op {
+ case OpSP:
+ sp = v
+ home = setloc(home, v, &registers[4]) // TODO: arch-dependent
+ case OpFP:
+ fp = v
+ home = setloc(home, v, &registers[16]) // TODO: arch-dependent
+ }
+ }
+
+ // Register allocate each block separately. All live values will live
+ // in home locations (stack slots) between blocks.
+ for _, b := range f.Blocks {
+
+ // Compute the index of the last use of each Value in the Block.
+ // Scheduling has already happened, so Values are totally ordered.
+ // lastUse[x] = max(i) where b.Value[i] uses Value x.
+ for i, v := range b.Values {
+ lastUse[v.ID] = -1
+ for _, w := range v.Args {
+ // could condition this store on w.Block == b, but no need
+ lastUse[w.ID] = i
+ }
+ }
+ // Values which are live at block exit have a lastUse of len(b.Values).
+ if b.Control != nil {
+ lastUse[b.Control.ID] = len(b.Values)
+ }
+ // Values live after block exit have a lastUse of len(b.Values)+1.
+ for _, vid := range live[b.ID] {
+ lastUse[vid] = len(b.Values) + 1
+ }
+
+ // For each register, store which value it contains
+ type regInfo struct {
+ v *Value // stack-homed original value (or nil if empty)
+ c *Value // the register copy of v
+ dirty bool // if the stack-homed copy is out of date
+ }
+ regs := make([]regInfo, numRegs)
+
+ // TODO: hack: initialize fixed registers
+ regs[4] = regInfo{sp, sp, false}
+ regs[16] = regInfo{fp, fp, false}
+
+ var used regMask // has a 1 for each non-nil entry in regs
+ var dirty regMask // has a 1 for each dirty entry in regs
+
+ oldSched = append(oldSched[:0], b.Values...)
+ b.Values = b.Values[:0]
+
+ for idx, v := range oldSched {
+ // For each instruction, do:
+ // set up inputs to v in registers
+ // pick output register
+ // run insn
+ // mark output register as dirty
+ // Note that v represents the Value at "home" (on the stack), and c
+ // is its register equivalent. There are two ways to establish c:
+ // - use of v. c will be a load from v's home.
+ // - definition of v. c will be identical to v but will live in
+ // a register. v will be modified into a spill of c.
+ regspec := opcodeTable[v.Op].reg
+ inputs := regspec[0]
+ outputs := regspec[1]
+ if len(inputs) == 0 && len(outputs) == 0 {
+ // No register allocation required (or none specified yet)
+ b.Values = append(b.Values, v)
+ continue
+ }
+
+ // Compute a good input ordering. Start with the most constrained input.
+ order := make([]intPair, len(inputs))
+ for i, input := range inputs {
+ order[i] = intPair{countRegs(input), i}
+ }
+ sort.Sort(byKey(order))
+
+ // nospill contains registers that we can't spill because
+ // we already set them up for use by the current instruction.
+ var nospill regMask
+ nospill |= 0x10010 // SP and FP can't be spilled (TODO: arch-specific)
+
+ // Move inputs into registers
+ for _, o := range order {
+ w := v.Args[o.val]
+ mask := inputs[o.val]
+ if mask == 0 {
+ // Input doesn't need a register
+ continue
+ }
+ // TODO: 2-address overwrite instructions
+
+ // Find registers that w is already in
+ var wreg regMask
+ for r := register(0); r < numRegs; r++ {
+ if regs[r].v == w {
+ wreg |= regMask(1) << r
+ }
+ }
+
+ var r register
+ if mask&wreg != 0 {
+ // w is already in an allowed register. We're done.
+ r = pickReg(mask & wreg)
+ } else {
+ // Pick a register for w
+ // Priorities (in order)
+ // - an unused register
+ // - a clean register
+ // - a dirty register
+ // TODO: for used registers, pick the one whose next use is the
+ // farthest in the future.
+ mask &^= nospill
+ if mask & ^dirty != 0 {
+ mask &^= dirty
+ }
+ if mask & ^used != 0 {
+ mask &^= used
+ }
+ r = pickReg(mask)
+
+ // Kick out whomever is using this register.
+ if regs[r].v != nil {
+ x := regs[r].v
+ c := regs[r].c
+ if regs[r].dirty && lastUse[x.ID] > idx {
+ // Write x back to home. Its value is currently held in c.
+ x.Op = OpStoreReg8
+ x.Aux = nil
+ x.resetArgs()
+ x.AddArg(c)
+ b.Values = append(b.Values, x)
+ regs[r].dirty = false
+ dirty &^= regMask(1) << r
+ }
+ regs[r].v = nil
+ regs[r].c = nil
+ used &^= regMask(1) << r
+ }
+
+ // Load w into this register
+ var c *Value
+ if len(w.Args) == 0 {
+ // Materialize w
+ if w.Op == OpFP || w.Op == OpSP || w.Op == OpGlobal {
+ c = b.NewValue1(OpCopy, w.Type, nil, w)
+ } else {
+ c = b.NewValue(w.Op, w.Type, w.Aux)
+ }
+ } else if len(w.Args) == 1 && (w.Args[0].Op == OpFP || w.Args[0].Op == OpSP || w.Args[0].Op == OpGlobal) {
+ // Materialize offsets from SP/FP/Global
+ c = b.NewValue1(w.Op, w.Type, w.Aux, w.Args[0])
+ } else if wreg != 0 {
+ // Copy from another register.
+ // Typically just an optimization, but this is
+ // required if w is dirty.
+ s := pickReg(wreg)
+ // inv: s != r
+ c = b.NewValue(OpCopy, w.Type, nil)
+ c.AddArg(regs[s].c)
+ } else {
+ // Load from home location
+ c = b.NewValue(OpLoadReg8, w.Type, nil)
+ c.AddArg(w)
+ }
+ home = setloc(home, c, &registers[r])
+ // Remember what we did
+ regs[r].v = w
+ regs[r].c = c
+ regs[r].dirty = false
+ used |= regMask(1) << r
+ }
+
+ // Replace w with its in-register copy.
+ v.SetArg(o.val, regs[r].c)
+
+ // Remember not to undo this register assignment until after
+ // the instruction is issued.
+ nospill |= regMask(1) << r
+ }
+
+ // pick a register for v itself.
+ if len(outputs) > 1 {
+ panic("can't do multi-output yet")
+ }
+ if len(outputs) == 0 || outputs[0] == 0 {
+ // output doesn't need a register
+ b.Values = append(b.Values, v)
+ } else {
+ mask := outputs[0]
+ if mask & ^dirty != 0 {
+ mask &^= dirty
+ }
+ if mask & ^used != 0 {
+ mask &^= used
+ }
+ r := pickReg(mask)
+
+ // Kick out whomever is using this register.
+ if regs[r].v != nil {
+ x := regs[r].v
+ c := regs[r].c
+ if regs[r].dirty && lastUse[x.ID] > idx {
+ // Write x back to home. Its value is currently held in c.
+ x.Op = OpStoreReg8
+ x.Aux = nil
+ x.resetArgs()
+ x.AddArg(c)
+ b.Values = append(b.Values, x)
+ regs[r].dirty = false
+ dirty &^= regMask(1) << r
+ }
+ regs[r].v = nil
+ regs[r].c = nil
+ used &^= regMask(1) << r
+ }
+
+ // Reissue v with new op, with r as its home.
+ c := b.NewValue(v.Op, v.Type, v.Aux)
+ c.AddArgs(v.Args...)
+ home = setloc(home, c, &registers[r])
+
+ // Remember what we did
+ regs[r].v = v
+ regs[r].c = c
+ regs[r].dirty = true
+ used |= regMask(1) << r
+ dirty |= regMask(1) << r
+ }
+ }
+
+ // If the block ends in a call, we must put the call after the spill code.
+ var call *Value
+ if b.Kind == BlockCall {
+ call = b.Control
+ if call != b.Values[len(b.Values)-1] {
+ log.Fatalf("call not at end of block %b %v", b, call)
+ }
+ b.Values = b.Values[:len(b.Values)-1]
+ // TODO: do this for all control types?
+ }
+
+ // at the end of the block, spill any remaining dirty, live values
+ for r := register(0); r < numRegs; r++ {
+ if !regs[r].dirty {
+ continue
+ }
+ v := regs[r].v
+ c := regs[r].c
+ if lastUse[v.ID] <= len(oldSched) {
+ if v == v.Block.Control {
+ // link control value to register version
+ v.Block.Control = c
+ }
+ continue // not live after block
+ }
+
+ // change v to be a copy of c
+ v.Op = OpStoreReg8
+ v.Aux = nil
+ v.resetArgs()
+ v.AddArg(c)
+ b.Values = append(b.Values, v)
+ }
+
+ // add call back after spills
+ if b.Kind == BlockCall {
+ b.Values = append(b.Values, call)
+ }
+ }
+ f.RegAlloc = home
+ deadcode(f) // remove values that had all of their uses rematerialized. TODO: separate pass?
+}
+
+// addPhiCopies adds copies of phi inputs in the blocks
+// immediately preceding the phi's block.
+func addPhiCopies(f *Func) {
+ for _, b := range f.Blocks {
+ for _, v := range b.Values {
+ if v.Op != OpPhi {
+ break // all phis should appear first
+ }
+ if v.Type.IsMemory() { // TODO: only "regallocable" types
+ continue
+ }
+ for i, w := range v.Args {
+ c := b.Preds[i]
+ cpy := c.NewValue1(OpCopy, v.Type, nil, w)
+ v.Args[i] = cpy
+ }
+ }
+ }
+}
+
+// live returns a map from block ID to a list of 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 live(f *Func) [][]ID {
+ live := make([][]ID, f.NumBlocks())
+ var phis []*Value
+
+ s := newSparseSet(f.NumValues())
+ t := newSparseSet(f.NumValues())
+ for {
+ for _, b := range f.Blocks {
+ fmt.Printf("live %s %v\n", b, live[b.ID])
+ }
+ changed := false
+
+ for _, b := range f.Blocks {
+ // Start with known live values at the end of the block
+ s.clear()
+ s.addAll(live[b.ID])
+
+ // Propagate backwards to the start of the block
+ // Assumes Values have been scheduled.
+ phis := phis[:0]
+ for i := len(b.Values) - 1; i >= 0; i-- {
+ v := b.Values[i]
+ s.remove(v.ID)
+ if v.Op == OpPhi {
+ // save phi ops for later
+ phis = append(phis, v)
+ continue
+ }
+ s.addAllValues(v.Args)
+ }
+
+ // for each predecessor of b, expand its list of live-at-end values
+ // inv: s contains the values live at the start of b (excluding phi inputs)
+ for i, p := range b.Preds {
+ t.clear()
+ t.addAll(live[p.ID])
+ t.addAll(s.contents())
+ for _, v := range phis {
+ t.add(v.Args[i].ID)
+ }
+ if t.size() == len(live[p.ID]) {
+ continue
+ }
+ // grow p's live set
+ c := make([]ID, t.size())
+ copy(c, t.contents())
+ live[p.ID] = c
+ changed = true
+ }
+ }
+
+ if !changed {
+ break
+ }
+ }
+ return live
+}
+
+// for sorting a pair of integers by key
+type intPair struct {
+ key, val int
+}
+type byKey []intPair
+
+func (a byKey) Len() int { return len(a) }
+func (a byKey) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
+func (a byKey) Less(i, j int) bool { return a[i].key < a[j].key }
generated by cgit v1.3-6-g1900 (git 2.53.0) at 2026-04-17 22:24:08 +0000