src/cmd/compile/internal/ssa/compile.go - go - Git at Google

 // 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/objabi"
 	"cmd/internal/src"
 	"fmt"
 	"hash/crc32"
 	"log"
 	"math/rand"
 	"os"
 	"regexp"
 	"runtime"
 	"strings"
 	"time"
 )

 // 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)
 	}

 	var rnd *rand.Rand
 	if checkEnabled {
 		rnd = rand.New(rand.NewSource(int64(crc32.ChecksumIEEE(([]byte)(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() {
 		printFunc(f)
 	}
 	f.HTMLWriter.WriteFunc("start", "start", f)
 	if BuildDump != "" && BuildDump == f.Name {
 		f.dumpFile("build")
 	}
 	if checkEnabled {
 		checkFunc(f)
 	}
 	const logMemStats = false
 	for _, p := range passes {
 		if !f.Config.optimize && !p.required || p.disabled {
 			continue
 		}
 		f.pass = &p
 		phaseName = p.name
 		if f.Log() {
 			f.Logf("  pass %s begin\n", p.name)
 		}
 		// TODO: capture logging during this pass, add it to the HTML
 		var mStart runtime.MemStats
 		if logMemStats || p.mem {
 			runtime.ReadMemStats(&mStart)
 		}

 		if checkEnabled && !f.scheduled {
 			// Test that we don't depend on the value order, by randomizing
 			// the order of values in each block. See issue 18169.
 			for _, b := range f.Blocks {
 				for i := 0; i < len(b.Values)-1; i++ {
 					j := i + rnd.Intn(len(b.Values)-i)
 					b.Values[i], b.Values[j] = b.Values[j], b.Values[i]
 				}
 			}
 		}

 		tStart := time.Now()
 		p.fn(f)
 		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
 				runtime.ReadMemStats(&mEnd)
 				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", p.name, stats)
 				printFunc(f)
 			}
 			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
 				runtime.ReadMemStats(&mEnd)
 				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
 			f.dumpFile(phaseName)
 		}
 		if checkEnabled {
 			checkFunc(f)
 		}
 	}

 	// 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) {
 	dumpFileSeq++
 	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)
 		return
 	}

 	p := stringFuncPrinter{w: fi}
 	fprintFunc(p, f)
 	fi.Close()
 }

 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(p.name, " ", "_", -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>]

 where:

 - <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.

 Examples:

     -d=ssa/check/on
 enables checking after each phase

     -d=ssa/all/time
 enables time reporting for all phases

     -d=ssa/prove/debug=2
 sets debugging level to 2 in the prove pass

 Multiple flags can be passed at once, by separating them with
 commas. For example:

     -d=ssa/check/on,ssa/all/time
 `
 	}

 	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
 		default:
 			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
 		default:
 			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 {
 				p.addDump(valString)
 			}
 			passes[i] = p
 			matchedOne = true
 		} else if p.name == phase || p.name == underphase || re != nil && re.MatchString(p.name) {
 			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":
 				p.addDump(valString)
 			default:
 				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 args", fn: decomposeArgs, required: true},
 	{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 p.name == a {
 				i = k
 			}
 			if p.name == 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)
 		}
 	}
 }
	// 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/objabi"
	"cmd/internal/src"
	"fmt"
	"hash/crc32"
	"log"
	"math/rand"
	"os"
	"regexp"
	"runtime"
	"strings"
	"time"
	)

	// 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)
	}

	var rnd *rand.Rand
	if checkEnabled {
	rnd = rand.New(rand.NewSource(int64(crc32.ChecksumIEEE(([]byte)(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() {
	printFunc(f)
	}
	f.HTMLWriter.WriteFunc("start", "start", f)
	if BuildDump != "" && BuildDump == f.Name {
	f.dumpFile("build")
	}
	if checkEnabled {
	checkFunc(f)
	}
	const logMemStats = false
	for _, p := range passes {
	if !f.Config.optimize && !p.required \|\| p.disabled {
	continue
	}
	f.pass = &p
	phaseName = p.name
	if f.Log() {
	f.Logf(" pass %s begin\n", p.name)
	}
	// TODO: capture logging during this pass, add it to the HTML
	var mStart runtime.MemStats
	if logMemStats \|\| p.mem {
	runtime.ReadMemStats(&mStart)
	}

	if checkEnabled && !f.scheduled {
	// Test that we don't depend on the value order, by randomizing
	// the order of values in each block. See issue 18169.
	for _, b := range f.Blocks {
	for i := 0; i < len(b.Values)-1; i++ {
	j := i + rnd.Intn(len(b.Values)-i)
	b.Values[i], b.Values[j] = b.Values[j], b.Values[i]
	}
	}
	}

	tStart := time.Now()
	p.fn(f)
	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
	runtime.ReadMemStats(&mEnd)
	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", p.name, stats)
	printFunc(f)
	}
	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
	runtime.ReadMemStats(&mEnd)
	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
	f.dumpFile(phaseName)
	}
	if checkEnabled {
	checkFunc(f)
	}
	}

	// 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) {
	dumpFileSeq++
	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)
	return
	}

	p := stringFuncPrinter{w: fi}
	fprintFunc(p, f)
	fi.Close()
	}

	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(p.name, " ", "_", -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>]

	where:

	- <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.

	Examples:

	-d=ssa/check/on
	enables checking after each phase

	-d=ssa/all/time
	enables time reporting for all phases

	-d=ssa/prove/debug=2
	sets debugging level to 2 in the prove pass

	Multiple flags can be passed at once, by separating them with
	commas. For example:

	-d=ssa/check/on,ssa/all/time
	`
	}

	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
	default:
	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
	default:
	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 {
	p.addDump(valString)
	}
	passes[i] = p
	matchedOne = true
	} else if p.name == phase \|\| p.name == underphase \|\| re != nil && re.MatchString(p.name) {
	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":
	p.addDump(valString)
	default:
	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 args", fn: decomposeArgs, required: true},
	{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 p.name == a {
	i = k
	}
	if p.name == 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)
	}
	}
	}