cmd/compile: add '-d=ssa/phase/@Keyword=value' option

This is intended to simplify tuning and experiments.

Change-Id: I8ec2245b868fe4d508df1bc880c69568c90d8f93
Reviewed-on: https://go-review.googlesource.com/c/go/+/803700
Reviewed-by: Jakub Ciolek <jakub@ciolek.dev>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>

Author: dr2chase

src/cmd/compile/internal/gc/compile.go

@@ -16,6 +16,7 @@ import (
 	"cmd/compile/internal/liveness"
 	"cmd/compile/internal/objw"
 	"cmd/compile/internal/pgoir"
+	"cmd/compile/internal/ssa"
 	"cmd/compile/internal/ssagen"
 	"cmd/compile/internal/staticinit"
 	"cmd/compile/internal/types"
@@ -189,4 +190,6 @@ func compileFunctions(profile *pgoir.Profile) {
 
 	base.Ctxt.InParallel = false
 	types.CalcSizeDisabled = false
+
+	ssa.PostCompile()
 }

src/cmd/compile/internal/ssa/compile.go

@@ -5,6 +5,7 @@
 package ssa
 
 import (
+	"cmd/compile/internal/base"
 	"cmd/internal/src"
 	"fmt"
 	"hash/crc32"
@@ -17,7 +18,9 @@ import (
 	"regexp"
 	"runtime"
 	"sort"
+	"strconv"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -202,12 +205,14 @@ type pass struct {
 	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
+	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
+	keywords map[string]int64 // ad hoc parameters, typically for experiments/tuning
+	usedKW   map[string]bool  // if a keyword is supplied to a phase, note that it was used.
 }
 
 func (p *pass) addDump(s string) {
@@ -224,6 +229,21 @@ func (p *pass) String() string {
 	return p.name
 }
 
+var kwMu sync.Mutex
+
+func (p *pass) Val(kw string, ifUnset int64) int64 {
+	if p == nil || p.keywords == nil {
+		return ifUnset
+	}
+	if v, ok := p.keywords[kw]; ok {
+		kwMu.Lock()
+		p.usedKW[kw] = true
+		kwMu.Unlock()
+		return v
+	}
+	return ifUnset
+}
+
 // Run consistency checker between each phase
 var (
 	checkEnabled  = false
@@ -283,7 +303,7 @@ where:
 ` + phasenames + `
 
 - <flag> is one of:
-    on, off, debug, mem, time, test, stats, dump, seed
+    on, off, debug, mem, time, test, stats, dump, seed, @<keyword>
 
 - <value> defaults to 1
 
@@ -438,7 +458,19 @@ commas. For example:
 			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 flag != "" && flag[0] == '@' {
+					if p.keywords == nil {
+						p.keywords = make(map[string]int64)
+						p.usedKW = make(map[string]bool)
+					}
+					val64, err := strconv.ParseInt(valString, 10, 64)
+					if err != nil {
+						return fmt.Sprintf("Failed to parse %s as integer value in -d=ssa/%s/%s=%s option", valString, phase, flag, valString)
+					}
+					p.keywords[flag[1:]] = int64(val64)
+				} else {
+					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)
@@ -612,6 +644,20 @@ var passOrder = [...]constraint{
 	{"prove", "known bits"},
 }
 
+func PostCompile() {
+	for _, c := range passes {
+		if c.keywords != nil {
+			for k := range c.keywords {
+				if !c.usedKW[k] {
+					// If someone specified a debugging keyword that was not
+					// consumed, they might want to know about this.
+					base.Warn("Keyword %s for pass %s was not used", k, c.name)
+				}
+			}
+		}
+	}
+}
+
 func init() {
 	for _, c := range passOrder {
 		a, b := c.a, c.b