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pass_blockmerge.go
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/
pass_blockmerge.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
// BlockMerge merges redundant intermediate blocks (blocks with a single
// outgoing edge which goes to another block with a single incoming edge).
type BlockMerge struct{}
func (BlockMerge) Apply(cfg *CFG) {
for {
var rt bool
var nx *BasicBlock
var it IrSuccessors
var tr IrTerminator
/* check every block */
cfg.PostOrder().ForEach(func(bb *BasicBlock) {
tr = bb.Term
it = tr.Successors()
/* it must have successors */
if !it.Next() {
return
}
/* it must have exactly 1 successor, and the successor must have exactly 1 predecessor */
if nx = it.Block(); it.Next() || len(nx.Pred) != 1 {
return
}
/* merge the two blocks */
rt = true
bb.Ins = append(bb.Ins, nx.Ins...)
bb.Term = nx.Term
/* must not have Phi nodes */
if len(nx.Phi) != 0 {
panic("invalid Phi node found in intermediate blocks")
}
/* get the successor iterator */
tr = nx.Term
it = tr.Successors()
/* update all predecessors references */
for it.Next() {
rb := it.Block()
pp := rb.Pred
/* update predecessor list */
for i, p := range pp {
if p == nx {
pp[i] = bb
}
}
/* update in Phi nodes */
for _, v := range rb.Phi {
v.V[bb] = v.V[nx]
delete(v.V, nx)
}
}
})
/* rebuild the dominator tree, and retry if needed */
if cfg.Rebuild(); !rt {
break
}
}
}