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// 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 (
// Compile is the main entry point for this package.
// Compile modifies f so that on return:
// · all Values in f map to 0 or 1 assembly instructions of the target architecture
// · the order of f.Blocks is the order to emit the Blocks
// · the order of b.Values is the order to emit the Values in each Block
// · f has a non-nil regAlloc field
func Compile(f *Func) {
// TODO: debugging - set flags to control verbosity of compiler,
// which phases to dump IR before/after, etc.
if f.Log() {
f.Logf("compiling %s\n", f.Name)
// hook to print function & phase if panic happens
phaseName := "init"
defer func() {
if phaseName != "" {
err := recover()
stack := make([]byte, 16384)
n := runtime.Stack(stack, false)
stack = stack[:n]
f.Fatalf("panic during %s while compiling %s:\n\n%v\n\n%s\n", phaseName, f.Name, err, stack)
// Run all the passes
if f.Log() {
f.HTMLWriter.WriteFunc("start", "start", f)
if BuildDump != "" && BuildDump == f.Name {
if checkEnabled {
const logMemStats = false
for _, p := range passes {
if !f.Config.optimize && !p.required || p.disabled {
f.pass = &p
phaseName =
if f.Log() {
f.Logf(" pass %s begin\n",
// TODO: capture logging during this pass, add it to the HTML
var mStart runtime.MemStats
if logMemStats || p.mem {
tStart := time.Now()
tEnd := time.Now()
// Need something less crude than "Log the whole intermediate result".
if f.Log() || f.HTMLWriter != nil {
time := tEnd.Sub(tStart).Nanoseconds()
var stats string
if logMemStats {
var mEnd runtime.MemStats
nBytes := mEnd.TotalAlloc - mStart.TotalAlloc
nAllocs := mEnd.Mallocs - mStart.Mallocs
stats = fmt.Sprintf("[%d ns %d allocs %d bytes]", time, nAllocs, nBytes)
} else {
stats = fmt.Sprintf("[%d ns]", time)
if f.Log() {
f.Logf(" pass %s end %s\n",, stats)
f.HTMLWriter.WriteFunc(phaseName, fmt.Sprintf("%s <span class=\"stats\">%s</span>", phaseName, stats), f)
if p.time || p.mem {
// Surround timing information w/ enough context to allow comparisons.
time := tEnd.Sub(tStart).Nanoseconds()
if p.time {
f.LogStat("TIME(ns)", time)
if p.mem {
var mEnd runtime.MemStats
nBytes := mEnd.TotalAlloc - mStart.TotalAlloc
nAllocs := mEnd.Mallocs - mStart.Mallocs
f.LogStat("TIME(ns):BYTES:ALLOCS", time, nBytes, nAllocs)
if p.dump != nil && p.dump[f.Name] {
// Dump function to appropriately named file
if checkEnabled {
// Squash error printing defer
phaseName = ""
// TODO: should be a config field
var dumpFileSeq int
// dumpFile creates a file from the phase name and function name
// Dumping is done to files to avoid buffering huge strings before
// output.
func (f *Func) dumpFile(phaseName string) {
fname := fmt.Sprintf("%s_%02d__%s.dump", f.Name, dumpFileSeq, phaseName)
fname = strings.Replace(fname, " ", "_", -1)
fname = strings.Replace(fname, "/", "_", -1)
fname = strings.Replace(fname, ":", "_", -1)
fi, err := os.Create(fname)
if err != nil {
f.Warnl(src.NoXPos, "Unable to create after-phase dump file %s", fname)
p := stringFuncPrinter{w: fi}
fprintFunc(p, f)
type pass struct {
name string
fn func(*Func)
required bool
disabled bool
time bool // report time to run pass
mem bool // report mem stats to run pass
stats int // pass reports own "stats" (e.g., branches removed)
debug int // pass performs some debugging. =1 should be in error-testing-friendly Warnl format.
test int // pass-specific ad-hoc option, perhaps useful in development
dump map[string]bool // dump if function name matches
func (p *pass) addDump(s string) {
if p.dump == nil {
p.dump = make(map[string]bool)
p.dump[s] = true
// Run consistency checker between each phase
var checkEnabled = false
// Debug output
var IntrinsicsDebug int
var IntrinsicsDisable bool
var BuildDebug int
var BuildTest int
var BuildStats int
var BuildDump string // name of function to dump after initial build of ssa
// PhaseOption sets the specified flag in the specified ssa phase,
// returning empty string if this was successful or a string explaining
// the error if it was not.
// A version of the phase name with "_" replaced by " " is also checked for a match.
// If the phase name begins a '~' then the rest of the underscores-replaced-with-blanks
// version is used as a regular expression to match the phase name(s).
// Special cases that have turned out to be useful:
// ssa/check/on enables checking after each phase
// ssa/all/time enables time reporting for all phases
// See gc/lex.go for dissection of the option string.
// Example uses:
// GO_GCFLAGS=-d=ssa/generic_cse/time,ssa/generic_cse/stats,ssa/generic_cse/debug=3 ./make.bash
// BOOT_GO_GCFLAGS=-d='ssa/~^.*scc$/off' GO_GCFLAGS='-d=ssa/~^.*scc$/off' ./make.bash
func PhaseOption(phase, flag string, val int, valString string) string {
if phase == "help" {
lastcr := 0
phasenames := " check, all, build, intrinsics"
for _, p := range passes {
pn := strings.Replace(, " ", "_", -1)
if len(pn)+len(phasenames)-lastcr > 70 {
phasenames += "\n "
lastcr = len(phasenames)
phasenames += pn
} else {
phasenames += ", " + pn
return `PhaseOptions usage:
go tool compile -d=ssa/<phase>/<flag>[=<value>|<function_name>]
- <phase> is one of:
` + phasenames + `
- <flag> is one of:
on, off, debug, mem, time, test, stats, dump
- <value> defaults to 1
- <function_name> is required for the "dump" flag, and specifies the
name of function to dump after <phase>
Phase "all" supports flags "time", "mem", and "dump".
Phase "intrinsics" supports flags "on", "off", and "debug".
If the "dump" flag is specified, the output is written on a file named
<phase>__<function_name>_<seq>.dump; otherwise it is directed to stdout.
enables checking after each phase
enables time reporting for all phases
sets debugging level to 2 in the prove pass
Multiple flags can be passed at once, by separating them with
commas. For example:
if phase == "check" && flag == "on" {
checkEnabled = val != 0
return ""
if phase == "check" && flag == "off" {
checkEnabled = val == 0
return ""
alltime := false
allmem := false
alldump := false
if phase == "all" {
if flag == "time" {
alltime = val != 0
} else if flag == "mem" {
allmem = val != 0
} else if flag == "dump" {
alldump = val != 0
if alldump {
BuildDump = valString
} else {
return fmt.Sprintf("Did not find a flag matching %s in -d=ssa/%s debug option", flag, phase)
if phase == "intrinsics" {
switch flag {
case "on":
IntrinsicsDisable = val == 0
case "off":
IntrinsicsDisable = val != 0
case "debug":
IntrinsicsDebug = val
return fmt.Sprintf("Did not find a flag matching %s in -d=ssa/%s debug option", flag, phase)
return ""
if phase == "build" {
switch flag {
case "debug":
BuildDebug = val
case "test":
BuildTest = val
case "stats":
BuildStats = val
case "dump":
BuildDump = valString
return fmt.Sprintf("Did not find a flag matching %s in -d=ssa/%s debug option", flag, phase)
return ""
underphase := strings.Replace(phase, "_", " ", -1)
var re *regexp.Regexp
if phase[0] == '~' {
r, ok := regexp.Compile(underphase[1:])
if ok != nil {
return fmt.Sprintf("Error %s in regexp for phase %s, flag %s", ok.Error(), phase, flag)
re = r
matchedOne := false
for i, p := range passes {
if phase == "all" {
p.time = alltime
p.mem = allmem
if alldump {
passes[i] = p
matchedOne = true
} else if == phase || == underphase || re != nil && re.MatchString( {
switch flag {
case "on":
p.disabled = val == 0
case "off":
p.disabled = val != 0
case "time":
p.time = val != 0
case "mem":
p.mem = val != 0
case "debug":
p.debug = val
case "stats":
p.stats = val
case "test":
p.test = val
case "dump":
return fmt.Sprintf("Did not find a flag matching %s in -d=ssa/%s debug option", flag, phase)
if p.disabled && p.required {
return fmt.Sprintf("Cannot disable required SSA phase %s using -d=ssa/%s debug option", phase, phase)
passes[i] = p
matchedOne = true
if matchedOne {
return ""
return fmt.Sprintf("Did not find a phase matching %s in -d=ssa/... debug option", phase)
// list of passes for the compiler
var passes = [...]pass{
// TODO: combine phielim and copyelim into a single pass?
{name: "number lines", fn: numberLines, required: true},
{name: "early phielim", fn: phielim},
{name: "early copyelim", fn: copyelim},
{name: "early deadcode", fn: deadcode}, // remove generated dead code to avoid doing pointless work during opt
{name: "short circuit", fn: shortcircuit},
{name: "decompose user", fn: decomposeUser, required: true},
{name: "opt", fn: opt, required: true}, // TODO: split required rules and optimizing rules
{name: "zero arg cse", fn: zcse, required: true}, // required to merge OpSB values
{name: "opt deadcode", fn: deadcode, required: true}, // remove any blocks orphaned during opt
{name: "generic cse", fn: cse},
{name: "phiopt", fn: phiopt},
{name: "nilcheckelim", fn: nilcheckelim},
{name: "prove", fn: prove},
{name: "fuse plain", fn: fusePlain},
{name: "decompose builtin", fn: decomposeBuiltIn, required: true},
{name: "softfloat", fn: softfloat, required: true},
{name: "late opt", fn: opt, required: true}, // TODO: split required rules and optimizing rules
{name: "dead auto elim", fn: elimDeadAutosGeneric},
{name: "generic deadcode", fn: deadcode, required: true}, // remove dead stores, which otherwise mess up store chain
{name: "check bce", fn: checkbce},
{name: "branchelim", fn: branchelim},
{name: "fuse", fn: fuseAll},
{name: "dse", fn: dse},
{name: "writebarrier", fn: writebarrier, required: true}, // expand write barrier ops
{name: "insert resched checks", fn: insertLoopReschedChecks,
disabled: objabi.Preemptibleloops_enabled == 0}, // insert resched checks in loops.
{name: "lower", fn: lower, required: true},
{name: "lowered cse", fn: cse},
{name: "elim unread autos", fn: elimUnreadAutos},
{name: "lowered deadcode", fn: deadcode, required: true},
{name: "checkLower", fn: checkLower, required: true},
{name: "late phielim", fn: phielim},
{name: "late copyelim", fn: copyelim},
{name: "tighten", fn: tighten}, // move values closer to their uses
{name: "phi tighten", fn: phiTighten},
{name: "late deadcode", fn: deadcode},
{name: "critical", fn: critical, required: true}, // remove critical edges
{name: "likelyadjust", fn: likelyadjust},
{name: "layout", fn: layout, required: true}, // schedule blocks
{name: "schedule", fn: schedule, required: true}, // schedule values
{name: "late nilcheck", fn: nilcheckelim2},
{name: "flagalloc", fn: flagalloc, required: true}, // allocate flags register
{name: "regalloc", fn: regalloc, required: true}, // allocate int & float registers + stack slots
{name: "loop rotate", fn: loopRotate},
{name: "stackframe", fn: stackframe, required: true},
{name: "trim", fn: trim}, // remove empty blocks
// Double-check phase ordering constraints.
// This code is intended to document the ordering requirements
// between different phases. It does not override the passes
// list above.
type constraint struct {
a, b string // a must come before b
var passOrder = [...]constraint{
// "insert resched checks" uses mem, better to clean out stores first.
{"dse", "insert resched checks"},
// insert resched checks adds new blocks containing generic instructions
{"insert resched checks", "lower"},
{"insert resched checks", "tighten"},
// prove relies on common-subexpression elimination for maximum benefits.
{"generic cse", "prove"},
// deadcode after prove to eliminate all new dead blocks.
{"prove", "generic deadcode"},
// common-subexpression before dead-store elim, so that we recognize
// when two address expressions are the same.
{"generic cse", "dse"},
// cse substantially improves nilcheckelim efficacy
{"generic cse", "nilcheckelim"},
// allow deadcode to clean up after nilcheckelim
{"nilcheckelim", "generic deadcode"},
// nilcheckelim generates sequences of plain basic blocks
{"nilcheckelim", "fuse"},
// nilcheckelim relies on opt to rewrite user nil checks
{"opt", "nilcheckelim"},
// tighten will be most effective when as many values have been removed as possible
{"generic deadcode", "tighten"},
{"generic cse", "tighten"},
// checkbce needs the values removed
{"generic deadcode", "check bce"},
// don't run optimization pass until we've decomposed builtin objects
{"decompose builtin", "late opt"},
// decompose builtin is the last pass that may introduce new float ops, so run softfloat after it
{"decompose builtin", "softfloat"},
// don't layout blocks until critical edges have been removed
{"critical", "layout"},
// regalloc requires the removal of all critical edges
{"critical", "regalloc"},
// regalloc requires all the values in a block to be scheduled
{"schedule", "regalloc"},
// checkLower must run after lowering & subsequent dead code elim
{"lower", "checkLower"},
{"lowered deadcode", "checkLower"},
// late nilcheck needs instructions to be scheduled.
{"schedule", "late nilcheck"},
// flagalloc needs instructions to be scheduled.
{"schedule", "flagalloc"},
// regalloc needs flags to be allocated first.
{"flagalloc", "regalloc"},
// loopRotate will confuse regalloc.
{"regalloc", "loop rotate"},
// stackframe needs to know about spilled registers.
{"regalloc", "stackframe"},
// trim needs regalloc to be done first.
{"regalloc", "trim"},
func init() {
for _, c := range passOrder {
a, b := c.a, c.b
i := -1
j := -1
for k, p := range passes {
if == a {
i = k
if == b {
j = k
if i < 0 {
log.Panicf("pass %s not found", a)
if j < 0 {
log.Panicf("pass %s not found", b)
if i >= j {
log.Panicf("passes %s and %s out of order", a, b)