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regalloc.go
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regalloc.go
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package gorgonia
import (
"fmt"
"io/ioutil"
"github.com/xtgo/set"
)
// this file holds all the code that relates to registrer allocation
// a lot of the code is shamelessly copied from my previous HIL work, the thirteenthfloor
// TODO: cleanup
type interval struct {
start, end int
result register
reads []register
ranges []intervalRange
usePositions []int
}
func newInterval() *interval {
retVal := &interval{
start: -1,
end: -1,
}
// switch vr.(type) {
// case *ssa.StaticSingleAssignment:
// retVal.isDestination = true
// case *ssa.Phi:
// case *ssa.Pop:
// retVal.isDestination = true
// default:
// }
return retVal
}
func (i *interval) String() string {
return fmt.Sprintf("%s | %d - %d | %v", i.result, i.start, i.end, i.usePositions)
}
func (i *interval) setFrom(from int) {
if i.start == -1 || (from < i.start && from >= 0) {
i.start = from
}
}
func (i *interval) fix() {
if len(i.usePositions) == 0 {
return
}
i.usePositions = set.Ints(i.usePositions)
i.end = i.usePositions[len(i.usePositions)-1]
for _, r := range i.ranges {
if r.to > i.end {
i.end = r.to
}
}
}
// func (i *interval) setTo(to int) {
// if to < i.start {
// // invalid To
// panic("to < start")
// }
// if to < i.end {
// uPs := i.usePositions
// sort.Ints(i.usePositions)
// maxUP := uPs[len(uPs)-1]
// if to >= maxUP {
// i.end = to
// }
// } else if to > i.end {
// i.end = to
// }
// }
func (i *interval) addRange(from, to int) {
if to < from {
panic("to < from") // note: to == from is a valid interval range
}
r := intervalRange{from, to}
// because I'm lazy to create a intervalRangeSet type, we'll just iterate and check
for _, ra := range i.ranges {
if r == ra {
return
}
}
i.ranges = append(i.ranges, r)
// set the end property
if to > i.end {
i.end = to
}
i.setFrom(from)
}
// added so only unique usePositions are added
func (i *interval) addUsePositions(up int) {
// for _, u := range i.usePositions {
// if u == up {
// return
// }
// }
// i.usePositions = append(i.usePositions, up)
// if i.end < up {
// i.setTo(up)
// }
i.usePositions = append(i.usePositions, up)
}
func (i *interval) noUsePositions() bool {
if len(i.usePositions) == 0 || i.usePositions == nil {
return true
}
return false
}
// inclusive of start, but exclusive of end
func (i *interval) liveAt(id int) bool {
compileLogf("%v live at %d", i, id)
if i.start <= id && id < i.end {
return true
}
return false
}
func (i *interval) merge(other *interval) {
if other.start < i.start && other.start >= 0 {
i.start = other.start
}
if other.end > i.end {
i.end = other.end
}
for _, r := range other.ranges {
i.addRange(r.from, r.to)
}
i.usePositions = append(i.usePositions, other.usePositions...)
i.usePositions = set.Ints(i.usePositions)
}
type intervalRange struct {
from, to int
}
/*
Notes on handling the live set:
1. We load all the SSAs listed in the block's LiveIn
2. Then we load all the SSAs used as input in this block Phi nodes
- The reason for this is so that those SSAs can have intervals created
that are live in this block (well, they are kinda live)
3. These input SSAs are temporary only, because a path-dependent liveset will be calculated below
Consider a CFG that looks like this:
BLOCK 1 BLOCK 3
+-------+ +-------+
+---->| x = 1 +------->| y = 3 +----------------+
BLOCK 0 | +-------+ | use x | v BLOCK 4
+-------+ | +-------+ +-------------+
| |+----+ | x = ϕ(1, 2) |
+-------+ | BLOCK 2 +-------------+
| +-------+ ^
+---->| x = 2 +---------------------------------+
+-------+
`x = 1` needs to be live in BLOCK 1, BLOCK 3 and BLOCK 4
`x = 2` needs to be live in BLOCK 2 and BLOCK 4.
The solution: in BLOCK 4, load `x = 1` and `x = 2` so they can be considered live in Block 4.
The interval building process comes to BLOCK 3 next. It considers the SSAs that are live in BLOCK 4.
If `x = 2` is live in BLOCK 4, it's Bad News with capital letters (see comment below).
The solution: remove the InputSSAs of the Phi nodes when we're leaving this block.
*/
// TODO: rephrase above to fit this package's function.
// It's like the above, but without basic blocks, phi nodes, etc, making it a LOT simpler
func buildIntervals(sorted Nodes) map[*Node]*interval {
intervals := make(map[*Node]*interval)
var g *ExprGraph
for _, n := range sorted {
if g == nil && n.g != nil {
g = n.g
}
intervals[n] = newInterval()
}
instructions := len(sorted)
for i, n := range sorted {
instrNum := instructions - 1 - i
nInter := intervals[n]
// inputs will be live the entire program
if n.isInput() {
nInter.addRange(instrNum, instructions)
continue
}
nInter.addRange(instrNum, instrNum)
// nInter.setFrom(instrNum)
// nInter.setTo(instrNum)
for _, child := range n.children {
iv, ok := intervals[child]
if !ok {
parents := g.to[n]
for i, from := range parents {
ioutil.WriteFile(fmt.Sprintf("n_%d.dot", i), []byte(from.ToDot()), 0644)
}
}
iv.addUsePositions(instrNum)
// iv.setTo(instrNum)
}
// assume all derivations will be used at the end
if len(n.derivOf) > 0 {
for _, d := range n.derivOf {
if d.isInput() {
nInter.addUsePositions(instructions)
break
}
}
}
}
for _, iv := range intervals {
iv.fix()
}
return intervals
}
type regalloc struct {
count int
instructionID int
df *dataflow
}
func newRegalloc(df *dataflow) *regalloc {
return ®alloc{
df: df,
}
}
func (ra *regalloc) newReg(device Device) register {
out := register{ra.count, device}
ra.count++
return out
}
func (ra *regalloc) allocArg(nInterv *interval) {
nInterv.result = ra.newReg(CPU)
}
func (ra *regalloc) allocMutableOp(node *Node, nInterv *interval) {
// create new write to if overwriteInput and the used register is stil live
compileLogf("NodeID: %x returns pointer", node.ID())
compileLogf("Op: %v", node.op)
enterLoggingContext()
defer leaveLoggingContext()
var writeTo register
var reads []*interval
for _, child := range node.children {
cReplace := ra.df.replacements[child]
repInterv := ra.df.intervals[cReplace]
reads = append(reads, repInterv)
}
var letStmts Nodes
for _, parent := range node.g.To(node) {
n := parent.(*Node)
compileLogf("Parent: %v | %T", n, n.op)
if n.isStmt {
// compileLogf("isStmt")
if _, ok := n.op.(letOp); ok {
letStmts = append(letStmts, n)
}
}
}
overwrites := node.op.OverwritesInput()
if overwrites >= 0 {
overwrittenIsLive := reads[overwrites].liveAt(ra.instructionID)
compileLogf("Overwrites : %v ", overwrites)
compileLogf("Overwritten (%v) is live at %d? %t", reads[overwrites], ra.instructionID, overwrittenIsLive)
compileLogf("Let Statements: %d | %v", len(letStmts), reads[overwrites])
// If the overwritten is not live, and the node does not call external processes (obiviating the need to prealloc)
// then we can directly overwrite the register.
if len(letStmts) == 1 || (!overwrittenIsLive && !node.op.CallsExtern()) {
writeTo = reads[overwrites].result
} else {
if _, ok := node.op.(CUDADoer); ok {
writeTo = ra.newReg(Device(0))
} else {
writeTo = ra.newReg(CPU)
}
}
} else {
compileLogf("New register")
if _, ok := node.op.(CUDADoer); ok {
writeTo = ra.newReg(Device(0))
} else {
writeTo = ra.newReg(CPU)
}
}
for _, r := range reads {
nInterv.reads = append(nInterv.reads, r.result)
}
nInterv.result = writeTo
}
func (ra *regalloc) allocImmutableOp(node *Node, nInterv *interval) {
var writeTo register
var reads []*interval
for _, child := range node.children {
cReplace := ra.df.replacements[child]
repInterv := ra.df.intervals[cReplace]
reads = append(reads, repInterv)
}
compileLogf("NodeID: %x does not returns pointer", node.ID())
if _, ok := node.op.(CUDADoer); ok {
writeTo = ra.newReg(Device(0))
} else {
writeTo = ra.newReg(CPU)
}
for _, r := range reads {
nInterv.reads = append(nInterv.reads, r.result)
}
nInterv.result = writeTo
}
func (ra *regalloc) alloc(sorted Nodes) {
compileLogf("Allocating registers")
enterLoggingContext()
defer leaveLoggingContext()
for i := len(sorted) - 1; i >= 0; i-- {
node := sorted[i]
replacement := ra.df.replacements[node]
nInterv := ra.df.intervals[replacement]
if node != replacement {
compileLogf("Merging")
ra.df.intervals[node].merge(nInterv)
}
compileLogf("Working on %v(%x). InstructionID: %d", node, node.ID(), ra.instructionID)
switch {
case node.isArg():
ra.allocArg(nInterv)
case node.op.ReturnsPtr():
ra.allocMutableOp(node, nInterv)
default:
ra.allocImmutableOp(node, nInterv)
}
compileLogf("n: %x; result: %v; reads: %v", node.ID(), nInterv.result, nInterv.reads)
ra.instructionID++
}
}