《Go 语言运行时原理》8.1 从源码到 SSA：编译阶段与 dump

package main

import "fmt"

// sum 是一个容易被 SSA pass 优化的函数：
// 循环里 s += i*2 会被强度削减（i*2 -> i<<1）并做边界检查消除。
func sum(n int) int {
	s := 0
	for i := 0; i < n; i++ {
		s += i * 2
	}
	return s
}

// pick 用来观察内联：小函数会被内联进调用者。
func pick(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func main() {
	fmt.Println(sum(10), pick(3, 7))
}

cd /tmp/gbrt3/ssa
GOSSAFUNC=sum GOTOOLCHAIN=go1.27.0 go build -o /dev/null .
ls -la ssa.html

Go build: Success
644  ssa.html  141.2K

start
number lines [1959 ns]
early phielim and copyelim [833 ns]
early deadcode [2417 ns]
short circuit [458 ns]
decompose user [125 ns]
pre-opt deadcode [1292 ns]
opt [2250 ns]
zero arg cse [1250 ns]
opt deadcode [1000 ns]
generic cse [4417 ns]
phiopt [208 ns]
gcse deadcode [958 ns]
nilcheckelim [3125 ns]
prove [12583 ns]
divisible [750 ns]
divmod [458 ns]
middle opt [2209 ns]
known bits [1583 ns]
early fuse [167 ns]
expand calls [3833 ns]
decompose builtin [1833 ns]
softfloat [83 ns]
branchelim [334 ns]
late opt [1958 ns]
dead auto elim [667 ns]
sccp [6750 ns]
generic deadcode [1583 ns]
late fuse [1333 ns]
check bce [42 ns]
dse [1000 ns]
memcombine [417 ns]
writebarrier [750 ns]
lower [4792 ns]
addressing modes [41 ns]
late lower [1083 ns]
pair [916 ns]
lowered deadcode for cse [1083 ns]
lowered cse [1250 ns]
elim unread autos [166 ns]
tighten tuple selectors [208 ns]
lowered deadcode [792 ns]
checkLower [167 ns]
loop invariant [3000 ns]
late phielim and copyelim [375 ns]
tighten [2542 ns]
late deadcode [1208 ns]
critical [333 ns]
phi tighten [125 ns]
likelyadjust [417 ns]
layout [667 ns]
schedule [2250 ns]
late nilcheck [792 ns]
flagalloc [1250 ns]
regalloc [21000 ns]
loop rotate [958 ns]
trim [125 ns]
genssa

// src/cmd/compile/internal/gc/main.go:Main（节选）
func Main(archInit func(*ssagen.ArchInfo)) {
	base.Timer.Start("fe", "init")
	...
	// Interleaved devirtualization and inlining.
	base.Timer.Start("fe", "devirtualize-and-inline")
	interleaved.DevirtualizeAndInlinePackage(typecheck.Target, profile)
	...
	// Escape analysis.
	base.Timer.Start("fe", "escapes")
	escape.Funcs(typecheck.Target.Funcs)
	...
	base.Timer.Start("be", "compilefuncs")
	...
}

// src/cmd/compile/internal/ssagen/ssa.go:buildssa（节选，约 294 行）
func buildssa(fn *ir.Func, worker int, isPgoHot bool) *ssa.Func {
	...
	ssa.Compile(s.f)
	...
}

// src/cmd/compile/internal/ssa/compile.go:Compile（节选，约 30 行）
func Compile(f *Func) {
	...
	f.HTMLWriter.WritePhase("start", "start")
	...
	for _, p := range passes {
		...
	}
}

// src/cmd/compile/internal/ssa/compile.go:passes（节选，约 457 行）
var passes = [...]pass{
	{name: "number lines", fn: numberLines, required: true},
	{name: "early phielim and copyelim", fn: copyelim},
	{name: "early deadcode", fn: deadcode},
	{name: "short circuit", fn: shortcircuit},
	{name: "decompose user", fn: decomposeUser, required: true},
	{name: "pre-opt deadcode", fn: deadcode},
	{name: "opt", fn: opt, required: true},
	...
	{name: "prove", fn: prove},
	...
	{name: "lower", fn: lower, required: true},
	...
	{name: "regalloc", fn: regalloc},
	...
}