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pass_rematerialize.go
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/
pass_rematerialize.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
// Rematerialize recalculates simple values to reduce register pressure.
type Rematerialize struct{}
func (Rematerialize) Apply(cfg *CFG) {
consts := make(map[Reg]_ConstData)
consts[Rz] = constint(0)
consts[Pn] = constptr(nil, Const)
/* Phase 1: Scan all the constants */
for _, bb := range cfg.PostOrder().Reversed() {
for _, v := range bb.Ins {
if r, x, ok := IrArchTryIntoConstInt(v); ok {
consts[r] = constint(x)
} else if r, p, ok := IrArchTryIntoConstPtr(v); ok {
consts[r] = constptr(p, Volatile)
}
}
}
/* Phase 2: Replace register copies with consts if possible */
cfg.PostOrder().ForEach(func(bb *BasicBlock) {
for i, v := range bb.Ins {
if d, s, ok := IrArchTryIntoCopy(v); ok {
if cc, ok := consts[s]; ok {
if cc.i {
bb.Ins[i] = IrArchConstInt(d, cc.v)
} else {
bb.Ins[i] = IrArchConstPtr(d, cc.p)
}
}
}
}
})
}