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pass_zeroreg.go
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pass_zeroreg.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 (
`runtime`
)
// ZeroReg replaces read to %z or %nil to a register that was
// initialized to zero for architectures that does not have constant
// zero registers, such as `x86_64`.
type ZeroReg struct{}
func (ZeroReg) replace(cfg *CFG) {
cfg.PostOrder().ForEach(func(bb *BasicBlock) {
var ok bool
var rr *Reg
var use IrUsages
/* create the instruction buffer */
ins := bb.Ins
bb.Ins = make([]IrNode, 0, len(ins))
/* zero register replacer */
replacez := func(v IrUsages, ins *[]IrNode, tail IrNode) {
var z Reg
var r *Reg
/* insert an zeroing instruction if needed */
for _, r = range v.Usages() {
if r.Kind() == K_zero {
z = cfg.CreateRegister(false)
*ins = append(*ins, IrArchZero(z))
break
}
}
/* substitute all the zero register usages */
for _, r = range v.Usages() {
if r.Kind() == K_zero {
*r = z
}
}
/* add the instruction if needed */
if tail != nil {
*ins = append(*ins, tail)
}
}
/* scan all the Phi nodes */
for _, p := range bb.Pred {
var z Reg
var v *IrPhi
/* insert an zeroing instruction to it's predecessor if needed */
for _, v = range bb.Phi {
if v.V[p].Kind() == K_zero {
z = cfg.CreateRegister(false)
p.Ins = append(p.Ins, IrArchZero(z))
break
}
}
/* substitute all the zero register usages */
for _, v = range bb.Phi {
if rr = v.V[p]; rr.Kind() == K_zero {
*rr = z
}
}
}
/* scan all the instructions */
for _, v := range ins {
if use, ok = v.(IrUsages); ok {
replacez(use, &bb.Ins, v)
} else {
bb.Ins = append(bb.Ins, v)
}
}
/* scan the terminator */
if use, ok = bb.Term.(IrUsages); ok {
replacez(use, &bb.Ins, nil)
}
})
}
//goland:noinspection GoBoolExpressions
func (self ZeroReg) Apply(cfg *CFG) {
if runtime.GOARCH == "amd64" {
self.replace(cfg)
}
}