| 1 | // Copyright 2022 The Go Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package ssa |
| 6 | |
| 7 | import "fmt" |
| 8 | |
| 9 | // This file implements the BasicBlock type. |
| 10 | |
| 11 | // addEdge adds a control-flow graph edge from from to to. |
| 12 | func addEdge(from, to *BasicBlock) { |
| 13 | from.Succs = append(from.Succs, to) |
| 14 | to.Preds = append(to.Preds, from) |
| 15 | } |
| 16 | |
| 17 | // Parent returns the function that contains block b. |
| 18 | func (b *BasicBlock) Parent() *Function { return b.parent } |
| 19 | |
| 20 | // String returns a human-readable label of this block. |
| 21 | // It is not guaranteed unique within the function. |
| 22 | func (b *BasicBlock) String() string { |
| 23 | return fmt.Sprintf("%d", b.Index) |
| 24 | } |
| 25 | |
| 26 | // emit appends an instruction to the current basic block. |
| 27 | // If the instruction defines a Value, it is returned. |
| 28 | func (b *BasicBlock) emit(i Instruction) Value { |
| 29 | i.setBlock(b) |
| 30 | b.Instrs = append(b.Instrs, i) |
| 31 | v, _ := i.(Value) |
| 32 | return v |
| 33 | } |
| 34 | |
| 35 | // predIndex returns the i such that b.Preds[i] == c or panics if |
| 36 | // there is none. |
| 37 | func (b *BasicBlock) predIndex(c *BasicBlock) int { |
| 38 | for i, pred := range b.Preds { |
| 39 | if pred == c { |
| 40 | return i |
| 41 | } |
| 42 | } |
| 43 | panic(fmt.Sprintf("no edge %s -> %s", c, b)) |
| 44 | } |
| 45 | |
| 46 | // hasPhi returns true if b.Instrs contains φ-nodes. |
| 47 | func (b *BasicBlock) hasPhi() bool { |
| 48 | _, ok := b.Instrs[0].(*Phi) |
| 49 | return ok |
| 50 | } |
| 51 | |
| 52 | // phis returns the prefix of b.Instrs containing all the block's φ-nodes. |
| 53 | func (b *BasicBlock) phis() []Instruction { |
| 54 | for i, instr := range b.Instrs { |
| 55 | if _, ok := instr.(*Phi); !ok { |
| 56 | return b.Instrs[:i] |
| 57 | } |
| 58 | } |
| 59 | return nil // unreachable in well-formed blocks |
| 60 | } |
| 61 | |
| 62 | // replacePred replaces all occurrences of p in b's predecessor list with q. |
| 63 | // Ordinarily there should be at most one. |
| 64 | func (b *BasicBlock) replacePred(p, q *BasicBlock) { |
| 65 | for i, pred := range b.Preds { |
| 66 | if pred == p { |
| 67 | b.Preds[i] = q |
| 68 | } |
| 69 | } |
| 70 | } |
| 71 | |
| 72 | // replaceSucc replaces all occurrences of p in b's successor list with q. |
| 73 | // Ordinarily there should be at most one. |
| 74 | func (b *BasicBlock) replaceSucc(p, q *BasicBlock) { |
| 75 | for i, succ := range b.Succs { |
| 76 | if succ == p { |
| 77 | b.Succs[i] = q |
| 78 | } |
| 79 | } |
| 80 | } |
| 81 | |
| 82 | // removePred removes all occurrences of p in b's |
| 83 | // predecessor list and φ-nodes. |
| 84 | // Ordinarily there should be at most one. |
| 85 | func (b *BasicBlock) removePred(p *BasicBlock) { |
| 86 | phis := b.phis() |
| 87 | |
| 88 | // We must preserve edge order for φ-nodes. |
| 89 | j := 0 |
| 90 | for i, pred := range b.Preds { |
| 91 | if pred != p { |
| 92 | b.Preds[j] = b.Preds[i] |
| 93 | // Strike out φ-edge too. |
| 94 | for _, instr := range phis { |
| 95 | phi := instr.(*Phi) |
| 96 | phi.Edges[j] = phi.Edges[i] |
| 97 | } |
| 98 | j++ |
| 99 | } |
| 100 | } |
| 101 | // Nil out b.Preds[j:] and φ-edges[j:] to aid GC. |
| 102 | for i := j; i < len(b.Preds); i++ { |
| 103 | b.Preds[i] = nil |
| 104 | for _, instr := range phis { |
| 105 | instr.(*Phi).Edges[i] = nil |
| 106 | } |
| 107 | } |
| 108 | b.Preds = b.Preds[:j] |
| 109 | for _, instr := range phis { |
| 110 | phi := instr.(*Phi) |
| 111 | phi.Edges = phi.Edges[:j] |
| 112 | } |
| 113 | } |
| 114 |
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