Gecko [ 167.86.127.34 ]

Name	Size	Permission
gen	[ DIR ]	drwxr-xr-x
testdata	[ DIR ]	drwxr-xr-x
README.md	7.76 KB	-rw-r--r--
TODO	950 B	-rw-r--r--
biasedsparsemap.go	2.71 KB	-rw-r--r--
block.go	8.64 KB	-rw-r--r--
branchelim.go	11.41 KB	-rw-r--r--
branchelim_test.go	5.21 KB	-rw-r--r--
cache.go	2.46 KB	-rw-r--r--
check.go	13.9 KB	-rw-r--r--
checkbce.go	956 B	-rw-r--r--
compile.go	16.22 KB	-rw-r--r--
config.go	11.39 KB	-rw-r--r--
copyelim.go	1.82 KB	-rw-r--r--
copyelim_test.go	1.29 KB	-rw-r--r--
critical.go	3.15 KB	-rw-r--r--
cse.go	10.62 KB	-rw-r--r--
cse_test.go	4.21 KB	-rw-r--r--
deadcode.go	9.73 KB	-rw-r--r--
deadcode_test.go	3.49 KB	-rw-r--r--
deadstore.go	8.98 KB	-rw-r--r--
deadstore_test.go	4.09 KB	-rw-r--r--
debug.go	33.92 KB	-rw-r--r--
debug_test.go	28.68 KB	-rw-r--r--
decompose.go	10.91 KB	-rw-r--r--
dom.go	7.98 KB	-rw-r--r--
dom_test.go	13.34 KB	-rw-r--r--
export_test.go	5.68 KB	-rw-r--r--
flagalloc.go	5.49 KB	-rw-r--r--
func.go	22.17 KB	-rw-r--r--
func_test.go	12.85 KB	-rw-r--r--
fuse.go	5.7 KB	-rw-r--r--
fuse_test.go	5.04 KB	-rw-r--r--
html.go	29.04 KB	-rw-r--r--
id.go	576 B	-rw-r--r--
layout.go	3.56 KB	-rw-r--r--
lca.go	3.71 KB	-rw-r--r--
lca_test.go	1.65 KB	-rw-r--r--
likelyadjust.go	15.23 KB	-rw-r--r--
location.go	2.8 KB	-rw-r--r--
loopbce.go	9.85 KB	-rw-r--r--
loopreschedchecks.go	15.36 KB	-rw-r--r--
looprotate.go	2.24 KB	-rw-r--r--
lower.go	1.24 KB	-rw-r--r--
magic.go	13.42 KB	-rw-r--r--
magic_test.go	9.1 KB	-rw-r--r--
nilcheck.go	11.11 KB	-rw-r--r--
nilcheck_test.go	12.07 KB	-rw-r--r--
numberlines.go	8.44 KB	-rw-r--r--
op.go	8.74 KB	-rw-r--r--
opGen.go	839.32 KB	-rw-r--r--
opt.go	290 B	-rw-r--r--
passbm_test.go	3.14 KB	-rw-r--r--
phielim.go	1.47 KB	-rw-r--r--
phiopt.go	3.96 KB	-rw-r--r--
poset.go	37.23 KB	-rw-r--r--
poset_test.go	18.14 KB	-rw-r--r--
print.go	2.98 KB	-rw-r--r--
prove.go	36.68 KB	-rw-r--r--
redblack32.go	8.9 KB	-rw-r--r--
redblack32_test.go	5.96 KB	-rw-r--r--
regalloc.go	76.36 KB	-rw-r--r--
regalloc_test.go	6.41 KB	-rw-r--r--
rewrite.go	33.06 KB	-rw-r--r--
rewrite386.go	514.14 KB	-rw-r--r--
rewrite386splitload.go	3.7 KB	-rw-r--r--
rewriteAMD64.go	1.31 MB	-rw-r--r--
rewriteAMD64splitload.go	4.95 KB	-rw-r--r--
rewriteARM.go	538.26 KB	-rw-r--r--
rewriteARM64.go	837.68 KB	-rw-r--r--
rewriteMIPS.go	203.31 KB	-rw-r--r--
rewriteMIPS64.go	227.84 KB	-rw-r--r--
rewritePPC64.go	661.88 KB	-rw-r--r--
rewriteRISCV64.go	123.11 KB	-rw-r--r--
rewriteS390X.go	904.36 KB	-rw-r--r--
rewriteWasm.go	136.86 KB	-rw-r--r--
rewrite_test.go	3.01 KB	-rw-r--r--
rewritedec.go	10.56 KB	-rw-r--r--
rewritedec64.go	64.01 KB	-rw-r--r--
rewritedecArgs.go	6.6 KB	-rw-r--r--
rewritegeneric.go	1.09 MB	-rw-r--r--
schedule.go	13.99 KB	-rw-r--r--
schedule_test.go	2.91 KB	-rw-r--r--
shift_test.go	4.05 KB	-rw-r--r--
shortcircuit.go	3.97 KB	-rw-r--r--
shortcircuit_test.go	1.31 KB	-rw-r--r--
sizeof_test.go	855 B	-rw-r--r--
softfloat.go	1.94 KB	-rw-r--r--
sparsemap.go	1.98 KB	-rw-r--r--
sparseset.go	1.54 KB	-rw-r--r--
sparsetree.go	7.88 KB	-rw-r--r--
sparsetreemap.go	7.67 KB	-rw-r--r--
stackalloc.go	10.95 KB	-rw-r--r--
stackframe.go	290 B	-rw-r--r--
stmtlines_test.go	2.75 KB	-rw-r--r--
tighten.go	4.21 KB	-rw-r--r--
trim.go	4.24 KB	-rw-r--r--
value.go	10.71 KB	-rw-r--r--
writebarrier.go	17.92 KB	-rw-r--r--
writebarrier_test.go	1.75 KB	-rw-r--r--
xposmap.go	3.29 KB	-rw-r--r--
zcse.go	2.12 KB	-rw-r--r--
zeroextension_test.go	1.66 KB	-rw-r--r--

Code Editor : fuse.go

// Copyright 2015 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 (
	"cmd/internal/src"
)

// fusePlain runs fuse(f, fuseTypePlain).
func fusePlain(f *Func) { fuse(f, fuseTypePlain) }

// fuseAll runs fuse(f, fuseTypeAll).
func fuseAll(f *Func) { fuse(f, fuseTypeAll) }

type fuseType uint8

const (
	fuseTypePlain fuseType = 1 << iota
	fuseTypeIf
	fuseTypeAll = fuseTypePlain | fuseTypeIf
)

// fuse simplifies control flow by joining basic blocks.
func fuse(f *Func, typ fuseType) {
	for changed := true; changed; {
		changed = false
		// Fuse from end to beginning, to avoid quadratic behavior in fuseBlockPlain. See issue 13554.
		for i := len(f.Blocks) - 1; i >= 0; i-- {
			b := f.Blocks[i]
			if typ&fuseTypeIf != 0 {
				changed = fuseBlockIf(b) || changed
			}
			if typ&fuseTypePlain != 0 {
				changed = fuseBlockPlain(b) || changed
			}
		}
		if changed {
			f.invalidateCFG()
		}
	}
}

// fuseBlockIf handles the following cases where s0 and s1 are empty blocks.
//
//   b        b        b      b
//  / \      | \      / |    | |
// s0  s1    |  s1   s0 |    | |
//  \ /      | /      \ |    | |
//   ss      ss        ss     ss
//
// If all Phi ops in ss have identical variables for slots corresponding to
// s0, s1 and b then the branch can be dropped.
// This optimization often comes up in switch statements with multiple
// expressions in a case clause:
//   switch n {
//     case 1,2,3: return 4
//   }
// TODO: If ss doesn't contain any OpPhis, are s0 and s1 dead code anyway.
func fuseBlockIf(b *Block) bool {
	if b.Kind != BlockIf {
		return false
	}

var ss0, ss1 *Block
	s0 := b.Succs[0].b
	i0 := b.Succs[0].i
	if s0.Kind != BlockPlain || len(s0.Preds) != 1 || !isEmpty(s0) {
		s0, ss0 = b, s0
	} else {
		ss0 = s0.Succs[0].b
		i0 = s0.Succs[0].i
	}
	s1 := b.Succs[1].b
	i1 := b.Succs[1].i
	if s1.Kind != BlockPlain || len(s1.Preds) != 1 || !isEmpty(s1) {
		s1, ss1 = b, s1
	} else {
		ss1 = s1.Succs[0].b
		i1 = s1.Succs[0].i
	}

if ss0 != ss1 {
		return false
	}
	ss := ss0

// s0 and s1 are equal with b if the corresponding block is missing
	// (2nd, 3rd and 4th case in the figure).

for _, v := range ss.Values {
		if v.Op == OpPhi && v.Uses > 0 && v.Args[i0] != v.Args[i1] {
			return false
		}
	}

// Now we have two of following b->ss, b->s0->ss and b->s1->ss,
	// with s0 and s1 empty if exist.
	// We can replace it with b->ss without if all OpPhis in ss
	// have identical predecessors (verified above).
	// No critical edge is introduced because b will have one successor.
	if s0 != b && s1 != b {
		// Replace edge b->s0->ss with b->ss.
		// We need to keep a slot for Phis corresponding to b.
		b.Succs[0] = Edge{ss, i0}
		ss.Preds[i0] = Edge{b, 0}
		b.removeEdge(1)
		s1.removeEdge(0)
	} else if s0 != b {
		b.removeEdge(0)
		s0.removeEdge(0)
	} else if s1 != b {
		b.removeEdge(1)
		s1.removeEdge(0)
	} else {
		b.removeEdge(1)
	}
	b.Kind = BlockPlain
	b.Likely = BranchUnknown
	b.ResetControls()

// Trash the empty blocks s0 and s1.
	blocks := [...]*Block{s0, s1}
	for _, s := range &blocks {
		if s == b {
			continue
		}
		// Move any (dead) values in s0 or s1 to b,
		// where they will be eliminated by the next deadcode pass.
		for _, v := range s.Values {
			v.Block = b
		}
		b.Values = append(b.Values, s.Values...)
		// Clear s.
		s.Kind = BlockInvalid
		s.Values = nil
		s.Succs = nil
		s.Preds = nil
	}
	return true
}

// isEmpty reports whether b contains any live values.
// There may be false positives.
func isEmpty(b *Block) bool {
	for _, v := range b.Values {
		if v.Uses > 0 || v.Op.IsCall() || v.Op.HasSideEffects() || v.Type.IsVoid() {
			return false
		}
	}
	return true
}

func fuseBlockPlain(b *Block) bool {
	if b.Kind != BlockPlain {
		return false
	}

c := b.Succs[0].b
	if len(c.Preds) != 1 {
		return false
	}

// If a block happened to end in a statement marker,
	// try to preserve it.
	if b.Pos.IsStmt() == src.PosIsStmt {
		l := b.Pos.Line()
		for _, v := range c.Values {
			if v.Pos.IsStmt() == src.PosNotStmt {
				continue
			}
			if l == v.Pos.Line() {
				v.Pos = v.Pos.WithIsStmt()
				l = 0
				break
			}
		}
		if l != 0 && c.Pos.Line() == l {
			c.Pos = c.Pos.WithIsStmt()
		}
	}

// move all of b's values to c.
	for _, v := range b.Values {
		v.Block = c
	}
	// Use whichever value slice is larger, in the hopes of avoiding growth.
	// However, take care to avoid c.Values pointing to b.valstorage.
	// See golang.org/issue/18602.
	// It's important to keep the elements in the same order; maintenance of
	// debugging information depends on the order of *Values in Blocks.
	// This can also cause changes in the order (which may affect other
	// optimizations and possibly compiler output) for 32-vs-64 bit compilation
	// platforms (word size affects allocation bucket size affects slice capacity).
	if cap(c.Values) >= cap(b.Values) || len(b.Values) <= len(b.valstorage) {
		bl := len(b.Values)
		cl := len(c.Values)
		var t []*Value // construct t = b.Values followed-by c.Values, but with attention to allocation.
		if cap(c.Values) < bl+cl {
			// reallocate
			t = make([]*Value, bl+cl)
		} else {
			// in place.
			t = c.Values[0 : bl+cl]
		}
		copy(t[bl:], c.Values) // possibly in-place
		c.Values = t
		copy(c.Values, b.Values)
	} else {
		c.Values = append(b.Values, c.Values...)
	}

// replace b->c edge with preds(b) -> c
	c.predstorage[0] = Edge{}
	if len(b.Preds) > len(b.predstorage) {
		c.Preds = b.Preds
	} else {
		c.Preds = append(c.predstorage[:0], b.Preds...)
	}
	for i, e := range c.Preds {
		p := e.b
		p.Succs[e.i] = Edge{c, i}
	}
	f := b.Func
	if f.Entry == b {
		f.Entry = c
	}

// trash b, just in case
	b.Kind = BlockInvalid
	b.Values = nil
	b.Preds = nil
	b.Succs = nil
	return true
}

${this.title}

Code Editor : fuse.go