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pass_comsubexpr.go
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/
pass_comsubexpr.go
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/*
* Copyright 2022 ByteDance Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package ssa
import (
`fmt`
)
type _Vid interface {
IrDefinitions
vid() []string
}
func (self *IrLoadArg) vid() []string {
return []string {
fmt.Sprintf("#%d", self.I),
}
}
func (self *IrLEA) vid() []string {
return []string {
fmt.Sprintf("(& %s %s)", self.Mem, self.Off),
}
}
func (self *IrUnaryExpr) vid() []string {
return []string {
fmt.Sprintf("(%s %s)", self.Op, self.V),
}
}
func (self *IrBinaryExpr) vid() []string {
x := self.X
y := self.Y
/* commutative operations, sort the operands */
switch self.Op {
case IrOpAdd : fallthrough
case IrOpMul : fallthrough
case IrOpAnd : fallthrough
case IrOpOr : fallthrough
case IrOpXor : fallthrough
case IrCmpEq : fallthrough
case IrCmpNe : if x > y { x, y = y, x }
}
/* build the value ID */
return []string {
fmt.Sprintf("(%s %s %s)", self.Op, x, y),
}
}
func (self *IrBitTestSet) vid() []string {
return []string {
fmt.Sprintf("(&# %s %s)", self.X, self.Y),
fmt.Sprintf("(|# %s %s)", self.X, self.Y),
}
}
type _VidMap struct {
p *_VidMap
m map[string]Reg
}
func (self *_VidMap) derive() *_VidMap {
return &_VidMap {
p: self,
m: make(map[string]Reg),
}
}
func (self *_VidMap) lookup(vid string) (Reg, bool) {
if r, ok := self.m[vid]; ok {
return r, true
} else if self.p == nil {
return 0, false
} else {
return self.p.lookup(vid)
}
}
func (self *_VidMap) define(vid string, reg Reg) {
self.m[vid] = reg
}
// CSE performs the Common Sub-expression Elimintation optimization.
type CSE struct{}
func (self CSE) dfs(cfg *CFG, bb *BasicBlock, vm *_VidMap) {
ins := bb.Ins
vals := vm.derive()
/* scan every instructions */
for i, v := range ins {
var r Reg
var d _Vid
var ok bool
/* check if the instruction have VIDs */
if d, ok = v.(_Vid); !ok {
continue
}
/* calculate the VIDs */
repc := i
vids := d.vid()
defs := d.Definitions()
/* replace each VID with a copy instruction */
for j, vid := range vids {
s := defs[j]
r, ok = vals.lookup(vid)
/* skip zero registers */
if s.Kind() == K_zero {
continue
}
/* add to definations if not found */
if !ok {
vals.define(vid, *s)
continue
}
/* allocate one slot for the new instruction */
repc++
bb.Ins = append(bb.Ins, nil)
copy(bb.Ins[repc + 1:], bb.Ins[repc:])
/* insert a new copy instruction */
bb.Ins[repc] = IrCopy(*s, r)
*s = s.Zero()
}
/* all the definations are been replaced */
if repc == i + len(defs) {
bb.Ins = append(bb.Ins[:i], bb.Ins[i + 1:]...)
}
}
/* DFS the dominator tree */
for _, v := range cfg.DominatorOf[bb.Id] {
self.dfs(cfg, v, vals)
}
}
func (self CSE) Apply(cfg *CFG) {
self.dfs(cfg, cfg.Root, nil)
}