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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssa
import "fmt"
// This file implements the BasicBlock type.
// addEdge adds a control-flow graph edge from from to to.
func addEdge(from, to *BasicBlock) {
from.Succs = append(from.Succs, to)
to.Preds = append(to.Preds, from)
}
// Parent returns the function that contains block b.
func (b *BasicBlock) Parent() *Function { return b.parent }
// String returns a human-readable label of this block.
// It is not guaranteed unique within the function.
func (b *BasicBlock) String() string {
return fmt.Sprintf("%d", b.Index)
}
// emit appends an instruction to the current basic block.
// If the instruction defines a Value, it is returned.
func (b *BasicBlock) emit(i Instruction) Value {
i.setBlock(b)
b.Instrs = append(b.Instrs, i)
v, _ := i.(Value)
return v
}
// predIndex returns the i such that b.Preds[i] == c or panics if
// there is none.
func (b *BasicBlock) predIndex(c *BasicBlock) int {
for i, pred := range b.Preds {
if pred == c {
return i
}
}
panic(fmt.Sprintf("no edge %s -> %s", c, b))
}
// hasPhi returns true if b.Instrs contains φ-nodes.
func (b *BasicBlock) hasPhi() bool {
_, ok := b.Instrs[0].(*Phi)
return ok
}
// phis returns the prefix of b.Instrs containing all the block's φ-nodes.
func (b *BasicBlock) phis() []Instruction {
for i, instr := range b.Instrs {
if _, ok := instr.(*Phi); !ok {
return b.Instrs[:i]
}
}
return nil // unreachable in well-formed blocks
}
// replacePred replaces all occurrences of p in b's predecessor list with q.
// Ordinarily there should be at most one.
func (b *BasicBlock) replacePred(p, q *BasicBlock) {
for i, pred := range b.Preds {
if pred == p {
b.Preds[i] = q
}
}
}
// replaceSucc replaces all occurrences of p in b's successor list with q.
// Ordinarily there should be at most one.
func (b *BasicBlock) replaceSucc(p, q *BasicBlock) {
for i, succ := range b.Succs {
if succ == p {
b.Succs[i] = q
}
}
}
// removePred removes all occurrences of p in b's
// predecessor list and φ-nodes.
// Ordinarily there should be at most one.
func (b *BasicBlock) removePred(p *BasicBlock) {
phis := b.phis()
// We must preserve edge order for φ-nodes.
j := 0
for i, pred := range b.Preds {
if pred != p {
b.Preds[j] = b.Preds[i]
// Strike out φ-edge too.
for _, instr := range phis {
phi := instr.(*Phi)
phi.Edges[j] = phi.Edges[i]
}
j++
}
}
// Nil out b.Preds[j:] and φ-edges[j:] to aid GC.
for i := j; i < len(b.Preds); i++ {
b.Preds[i] = nil
for _, instr := range phis {
instr.(*Phi).Edges[i] = nil
}
}
b.Preds = b.Preds[:j]
for _, instr := range phis {
phi := instr.(*Phi)
phi.Edges = phi.Edges[:j]
}
}
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