From: Alberto Donizetti <alb.donizetti@gmail.com>
Date: Mon, 19 Oct 2020 09:31:10 +0000 (+0200)
Subject: cmd/compile: make gc debug flags collector a struct
X-Git-Tag: go1.16beta1~607
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=3bac5faa4af2f5c454b2cebaa8be5cde9b8e2add;p=gostls13.git

cmd/compile: make gc debug flags collector a struct

gc debug flags are currently stored in a 256-long array, that is then
addressed using the ASCII numeric value of the flag itself (a quirk
inherited from the old C compiler). It is also a little wasteful,
since we only define 16 flags, and the other 240 array elements are
always empty.

This change makes Debug a struct, which also provides static checking
that we're not referencing flags that does not exist.

Change-Id: I2f0dfef2529325514b3398cf78635543cdf48fe0
Reviewed-on: https://go-review.googlesource.com/c/go/+/263539
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
---

diff --git a/src/cmd/compile/internal/gc/alg.go b/src/cmd/compile/internal/gc/alg.go
index 6302b88f59..2ab69c2c56 100644
--- a/src/cmd/compile/internal/gc/alg.go
+++ b/src/cmd/compile/internal/gc/alg.go
@@ -282,7 +282,7 @@ func genhash(t *types.Type) *obj.LSym {
 	}
 
 	sym := typesymprefix(".hash", t)
-	if Debug['r'] != 0 {
+	if Debug.r != 0 {
 		fmt.Printf("genhash %v %v %v\n", closure, sym, t)
 	}
 
@@ -374,7 +374,7 @@ func genhash(t *types.Type) *obj.LSym {
 	r.List.Append(nh)
 	fn.Nbody.Append(r)
 
-	if Debug['r'] != 0 {
+	if Debug.r != 0 {
 		dumplist("genhash body", fn.Nbody)
 	}
 
@@ -509,7 +509,7 @@ func geneq(t *types.Type) *obj.LSym {
 		return closure
 	}
 	sym := typesymprefix(".eq", t)
-	if Debug['r'] != 0 {
+	if Debug.r != 0 {
 		fmt.Printf("geneq %v\n", t)
 	}
 
@@ -732,7 +732,7 @@ func geneq(t *types.Type) *obj.LSym {
 		fn.Nbody.Append(ret)
 	}
 
-	if Debug['r'] != 0 {
+	if Debug.r != 0 {
 		dumplist("geneq body", fn.Nbody)
 	}
 
diff --git a/src/cmd/compile/internal/gc/closure.go b/src/cmd/compile/internal/gc/closure.go
index 5d1012111f..902d2e34a3 100644
--- a/src/cmd/compile/internal/gc/closure.go
+++ b/src/cmd/compile/internal/gc/closure.go
@@ -198,7 +198,7 @@ func capturevars(xfunc *Node) {
 			outer = nod(OADDR, outer, nil)
 		}
 
-		if Debug['m'] > 1 {
+		if Debug.m > 1 {
 			var name *types.Sym
 			if v.Name.Curfn != nil && v.Name.Curfn.Func.Nname != nil {
 				name = v.Name.Curfn.Func.Nname.Sym
diff --git a/src/cmd/compile/internal/gc/esc.go b/src/cmd/compile/internal/gc/esc.go
index c11066a62f..6f328ab5ea 100644
--- a/src/cmd/compile/internal/gc/esc.go
+++ b/src/cmd/compile/internal/gc/esc.go
@@ -282,7 +282,7 @@ func addrescapes(n *Node) {
 
 // moveToHeap records the parameter or local variable n as moved to the heap.
 func moveToHeap(n *Node) {
-	if Debug['r'] != 0 {
+	if Debug.r != 0 {
 		Dump("MOVE", n)
 	}
 	if compiling_runtime {
@@ -359,7 +359,7 @@ func moveToHeap(n *Node) {
 	n.Xoffset = 0
 	n.Name.Param.Heapaddr = heapaddr
 	n.Esc = EscHeap
-	if Debug['m'] != 0 {
+	if Debug.m != 0 {
 		Warnl(n.Pos, "moved to heap: %v", n)
 	}
 }
@@ -389,7 +389,7 @@ func (e *Escape) paramTag(fn *Node, narg int, f *types.Field) string {
 		// but we are reusing the ability to annotate an individual function
 		// argument and pass those annotations along to importing code.
 		if f.Type.IsUintptr() {
-			if Debug['m'] != 0 {
+			if Debug.m != 0 {
 				Warnl(f.Pos, "assuming %v is unsafe uintptr", name())
 			}
 			return unsafeUintptrTag
@@ -404,11 +404,11 @@ func (e *Escape) paramTag(fn *Node, narg int, f *types.Field) string {
 		// External functions are assumed unsafe, unless
 		// //go:noescape is given before the declaration.
 		if fn.Func.Pragma&Noescape != 0 {
-			if Debug['m'] != 0 && f.Sym != nil {
+			if Debug.m != 0 && f.Sym != nil {
 				Warnl(f.Pos, "%v does not escape", name())
 			}
 		} else {
-			if Debug['m'] != 0 && f.Sym != nil {
+			if Debug.m != 0 && f.Sym != nil {
 				Warnl(f.Pos, "leaking param: %v", name())
 			}
 			esc.AddHeap(0)
@@ -419,14 +419,14 @@ func (e *Escape) paramTag(fn *Node, narg int, f *types.Field) string {
 
 	if fn.Func.Pragma&UintptrEscapes != 0 {
 		if f.Type.IsUintptr() {
-			if Debug['m'] != 0 {
+			if Debug.m != 0 {
 				Warnl(f.Pos, "marking %v as escaping uintptr", name())
 			}
 			return uintptrEscapesTag
 		}
 		if f.IsDDD() && f.Type.Elem().IsUintptr() {
 			// final argument is ...uintptr.
-			if Debug['m'] != 0 {
+			if Debug.m != 0 {
 				Warnl(f.Pos, "marking %v as escaping ...uintptr", name())
 			}
 			return uintptrEscapesTag
@@ -448,7 +448,7 @@ func (e *Escape) paramTag(fn *Node, narg int, f *types.Field) string {
 	esc := loc.paramEsc
 	esc.Optimize()
 
-	if Debug['m'] != 0 && !loc.escapes {
+	if Debug.m != 0 && !loc.escapes {
 		if esc.Empty() {
 			Warnl(f.Pos, "%v does not escape", name())
 		}
diff --git a/src/cmd/compile/internal/gc/escape.go b/src/cmd/compile/internal/gc/escape.go
index 93965d4fac..618bdf78e2 100644
--- a/src/cmd/compile/internal/gc/escape.go
+++ b/src/cmd/compile/internal/gc/escape.go
@@ -170,7 +170,7 @@ func (e *Escape) initFunc(fn *Node) {
 		Fatalf("unexpected node: %v", fn)
 	}
 	fn.Esc = EscFuncPlanned
-	if Debug['m'] > 3 {
+	if Debug.m > 3 {
 		Dump("escAnalyze", fn)
 	}
 
@@ -247,7 +247,7 @@ func (e *Escape) stmt(n *Node) {
 		lineno = lno
 	}()
 
-	if Debug['m'] > 2 {
+	if Debug.m > 2 {
 		fmt.Printf("%v:[%d] %v stmt: %v\n", linestr(lineno), e.loopDepth, funcSym(e.curfn), n)
 	}
 
@@ -275,11 +275,11 @@ func (e *Escape) stmt(n *Node) {
 	case OLABEL:
 		switch asNode(n.Sym.Label) {
 		case &nonlooping:
-			if Debug['m'] > 2 {
+			if Debug.m > 2 {
 				fmt.Printf("%v:%v non-looping label\n", linestr(lineno), n)
 			}
 		case &looping:
-			if Debug['m'] > 2 {
+			if Debug.m > 2 {
 				fmt.Printf("%v: %v looping label\n", linestr(lineno), n)
 			}
 			e.loopDepth++
@@ -717,7 +717,7 @@ func (e *Escape) addrs(l Nodes) []EscHole {
 func (e *Escape) assign(dst, src *Node, why string, where *Node) {
 	// Filter out some no-op assignments for escape analysis.
 	ignore := dst != nil && src != nil && isSelfAssign(dst, src)
-	if ignore && Debug['m'] != 0 {
+	if ignore && Debug.m != 0 {
 		Warnl(where.Pos, "%v ignoring self-assignment in %S", funcSym(e.curfn), where)
 	}
 
@@ -931,7 +931,7 @@ func (k EscHole) note(where *Node, why string) EscHole {
 	if where == nil || why == "" {
 		Fatalf("note: missing where/why")
 	}
-	if Debug['m'] >= 2 || logopt.Enabled() {
+	if Debug.m >= 2 || logopt.Enabled() {
 		k.notes = &EscNote{
 			next:  k.notes,
 			where: where,
@@ -1077,9 +1077,9 @@ func (e *Escape) flow(k EscHole, src *EscLocation) {
 		return
 	}
 	if dst.escapes && k.derefs < 0 { // dst = &src
-		if Debug['m'] >= 2 || logopt.Enabled() {
+		if Debug.m >= 2 || logopt.Enabled() {
 			pos := linestr(src.n.Pos)
-			if Debug['m'] >= 2 {
+			if Debug.m >= 2 {
 				fmt.Printf("%s: %v escapes to heap:\n", pos, src.n)
 			}
 			explanation := e.explainFlow(pos, dst, src, k.derefs, k.notes, []*logopt.LoggedOpt{})
@@ -1179,8 +1179,8 @@ func (e *Escape) walkOne(root *EscLocation, walkgen uint32, enqueue func(*EscLoc
 			// that value flow for tagging the function
 			// later.
 			if l.isName(PPARAM) {
-				if (logopt.Enabled() || Debug['m'] >= 2) && !l.escapes {
-					if Debug['m'] >= 2 {
+				if (logopt.Enabled() || Debug.m >= 2) && !l.escapes {
+					if Debug.m >= 2 {
 						fmt.Printf("%s: parameter %v leaks to %s with derefs=%d:\n", linestr(l.n.Pos), l.n, e.explainLoc(root), base)
 					}
 					explanation := e.explainPath(root, l)
@@ -1196,8 +1196,8 @@ func (e *Escape) walkOne(root *EscLocation, walkgen uint32, enqueue func(*EscLoc
 			// outlives it, then l needs to be heap
 			// allocated.
 			if addressOf && !l.escapes {
-				if logopt.Enabled() || Debug['m'] >= 2 {
-					if Debug['m'] >= 2 {
+				if logopt.Enabled() || Debug.m >= 2 {
+					if Debug.m >= 2 {
 						fmt.Printf("%s: %v escapes to heap:\n", linestr(l.n.Pos), l.n)
 					}
 					explanation := e.explainPath(root, l)
@@ -1235,7 +1235,7 @@ func (e *Escape) explainPath(root, src *EscLocation) []*logopt.LoggedOpt {
 	for {
 		// Prevent infinite loop.
 		if visited[src] {
-			if Debug['m'] >= 2 {
+			if Debug.m >= 2 {
 				fmt.Printf("%s:   warning: truncated explanation due to assignment cycle; see golang.org/issue/35518\n", pos)
 			}
 			break
@@ -1263,7 +1263,7 @@ func (e *Escape) explainFlow(pos string, dst, srcloc *EscLocation, derefs int, n
 	if derefs >= 0 {
 		ops = strings.Repeat("*", derefs)
 	}
-	print := Debug['m'] >= 2
+	print := Debug.m >= 2
 
 	flow := fmt.Sprintf("   flow: %s = %s%v:", e.explainLoc(dst), ops, e.explainLoc(srcloc))
 	if print {
@@ -1417,7 +1417,7 @@ func (e *Escape) finish(fns []*Node) {
 
 		if loc.escapes {
 			if n.Op != ONAME {
-				if Debug['m'] != 0 {
+				if Debug.m != 0 {
 					Warnl(n.Pos, "%S escapes to heap", n)
 				}
 				if logopt.Enabled() {
@@ -1427,7 +1427,7 @@ func (e *Escape) finish(fns []*Node) {
 			n.Esc = EscHeap
 			addrescapes(n)
 		} else {
-			if Debug['m'] != 0 && n.Op != ONAME {
+			if Debug.m != 0 && n.Op != ONAME {
 				Warnl(n.Pos, "%S does not escape", n)
 			}
 			n.Esc = EscNone
diff --git a/src/cmd/compile/internal/gc/export.go b/src/cmd/compile/internal/gc/export.go
index 839c2c2c75..c6917e0f81 100644
--- a/src/cmd/compile/internal/gc/export.go
+++ b/src/cmd/compile/internal/gc/export.go
@@ -31,7 +31,7 @@ func exportsym(n *Node) {
 	}
 	n.Sym.SetOnExportList(true)
 
-	if Debug['E'] != 0 {
+	if Debug.E != 0 {
 		fmt.Printf("export symbol %v\n", n.Sym)
 	}
 
@@ -150,7 +150,7 @@ func importconst(ipkg *types.Pkg, pos src.XPos, s *types.Sym, t *types.Type, val
 
 	n.SetVal(val)
 
-	if Debug['E'] != 0 {
+	if Debug.E != 0 {
 		fmt.Printf("import const %v %L = %v\n", s, t, val)
 	}
 }
@@ -166,7 +166,7 @@ func importfunc(ipkg *types.Pkg, pos src.XPos, s *types.Sym, t *types.Type) {
 	n.Func = new(Func)
 	t.SetNname(asTypesNode(n))
 
-	if Debug['E'] != 0 {
+	if Debug.E != 0 {
 		fmt.Printf("import func %v%S\n", s, t)
 	}
 }
@@ -179,7 +179,7 @@ func importvar(ipkg *types.Pkg, pos src.XPos, s *types.Sym, t *types.Type) {
 		return
 	}
 
-	if Debug['E'] != 0 {
+	if Debug.E != 0 {
 		fmt.Printf("import var %v %L\n", s, t)
 	}
 }
@@ -192,7 +192,7 @@ func importalias(ipkg *types.Pkg, pos src.XPos, s *types.Sym, t *types.Type) {
 		return
 	}
 
-	if Debug['E'] != 0 {
+	if Debug.E != 0 {
 		fmt.Printf("import type %v = %L\n", s, t)
 	}
 }
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index ee2add3733..da6b6d6e72 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -116,7 +116,15 @@ var decldepth int32
 
 var nolocalimports bool
 
-var Debug [256]int
+// gc debug flags
+type DebugFlags struct {
+	P, B, C, E,
+	K, L, N, S,
+	W, e, h, j,
+	l, m, r, w int
+}
+
+var Debug DebugFlags
 
 var debugstr string
 
diff --git a/src/cmd/compile/internal/gc/gsubr.go b/src/cmd/compile/internal/gc/gsubr.go
index 14c217ff3b..ce5182f203 100644
--- a/src/cmd/compile/internal/gc/gsubr.go
+++ b/src/cmd/compile/internal/gc/gsubr.go
@@ -153,7 +153,7 @@ func (pp *Progs) Prog(as obj.As) *obj.Prog {
 	pp.clearp(pp.next)
 	p.Link = pp.next
 
-	if !pp.pos.IsKnown() && Debug['K'] != 0 {
+	if !pp.pos.IsKnown() && Debug.K != 0 {
 		Warn("prog: unknown position (line 0)")
 	}
 
diff --git a/src/cmd/compile/internal/gc/iimport.go b/src/cmd/compile/internal/gc/iimport.go
index 107e96cc6a..7f2b05f288 100644
--- a/src/cmd/compile/internal/gc/iimport.go
+++ b/src/cmd/compile/internal/gc/iimport.go
@@ -742,8 +742,8 @@ func (r *importReader) doInline(n *Node) {
 
 	importlist = append(importlist, n)
 
-	if Debug['E'] > 0 && Debug['m'] > 2 {
-		if Debug['m'] > 3 {
+	if Debug.E > 0 && Debug.m > 2 {
+		if Debug.m > 3 {
 			fmt.Printf("inl body for %v %#v: %+v\n", n, n.Type, asNodes(n.Func.Inl.Body))
 		} else {
 			fmt.Printf("inl body for %v %#v: %v\n", n, n.Type, asNodes(n.Func.Inl.Body))
diff --git a/src/cmd/compile/internal/gc/inl.go b/src/cmd/compile/internal/gc/inl.go
index 55a14d378e..a2fb00e132 100644
--- a/src/cmd/compile/internal/gc/inl.go
+++ b/src/cmd/compile/internal/gc/inl.go
@@ -7,7 +7,7 @@
 // saves a copy of the body. Then inlcalls walks each function body to
 // expand calls to inlinable functions.
 //
-// The debug['l'] flag controls the aggressiveness. Note that main() swaps level 0 and 1,
+// The Debug.l flag controls the aggressiveness. Note that main() swaps level 0 and 1,
 // making 1 the default and -l disable. Additional levels (beyond -l) may be buggy and
 // are not supported.
 //      0: disabled
@@ -21,7 +21,7 @@
 // The -d typcheckinl flag enables early typechecking of all imported bodies,
 // which is useful to flush out bugs.
 //
-// The debug['m'] flag enables diagnostic output.  a single -m is useful for verifying
+// The Debug.m flag enables diagnostic output.  a single -m is useful for verifying
 // which calls get inlined or not, more is for debugging, and may go away at any point.
 
 package gc
@@ -85,7 +85,7 @@ func typecheckinl(fn *Node) {
 		return // typecheckinl on local function
 	}
 
-	if Debug['m'] > 2 || Debug_export != 0 {
+	if Debug.m > 2 || Debug_export != 0 {
 		fmt.Printf("typecheck import [%v] %L { %#v }\n", fn.Sym, fn, asNodes(fn.Func.Inl.Body))
 	}
 
@@ -116,10 +116,10 @@ func caninl(fn *Node) {
 	}
 
 	var reason string // reason, if any, that the function was not inlined
-	if Debug['m'] > 1 || logopt.Enabled() {
+	if Debug.m > 1 || logopt.Enabled() {
 		defer func() {
 			if reason != "" {
-				if Debug['m'] > 1 {
+				if Debug.m > 1 {
 					fmt.Printf("%v: cannot inline %v: %s\n", fn.Line(), fn.Func.Nname, reason)
 				}
 				if logopt.Enabled() {
@@ -187,7 +187,7 @@ func caninl(fn *Node) {
 	defer n.Func.SetInlinabilityChecked(true)
 
 	cc := int32(inlineExtraCallCost)
-	if Debug['l'] == 4 {
+	if Debug.l == 4 {
 		cc = 1 // this appears to yield better performance than 0.
 	}
 
@@ -224,9 +224,9 @@ func caninl(fn *Node) {
 	// this is so export can find the body of a method
 	fn.Type.FuncType().Nname = asTypesNode(n)
 
-	if Debug['m'] > 1 {
+	if Debug.m > 1 {
 		fmt.Printf("%v: can inline %#v with cost %d as: %#v { %#v }\n", fn.Line(), n, inlineMaxBudget-visitor.budget, fn.Type, asNodes(n.Func.Inl.Body))
-	} else if Debug['m'] != 0 {
+	} else if Debug.m != 0 {
 		fmt.Printf("%v: can inline %v\n", fn.Line(), n)
 	}
 	if logopt.Enabled() {
@@ -425,7 +425,7 @@ func (v *hairyVisitor) visit(n *Node) bool {
 	v.budget--
 
 	// When debugging, don't stop early, to get full cost of inlining this function
-	if v.budget < 0 && Debug['m'] < 2 && !logopt.Enabled() {
+	if v.budget < 0 && Debug.m < 2 && !logopt.Enabled() {
 		return true
 	}
 
@@ -670,7 +670,7 @@ func inlnode(n *Node, maxCost int32, inlMap map[*Node]bool) *Node {
 
 	switch n.Op {
 	case OCALLFUNC:
-		if Debug['m'] > 3 {
+		if Debug.m > 3 {
 			fmt.Printf("%v:call to func %+v\n", n.Line(), n.Left)
 		}
 		if isIntrinsicCall(n) {
@@ -681,7 +681,7 @@ func inlnode(n *Node, maxCost int32, inlMap map[*Node]bool) *Node {
 		}
 
 	case OCALLMETH:
-		if Debug['m'] > 3 {
+		if Debug.m > 3 {
 			fmt.Printf("%v:call to meth %L\n", n.Line(), n.Left.Right)
 		}
 
@@ -911,7 +911,7 @@ func mkinlcall(n, fn *Node, maxCost int32, inlMap map[*Node]bool) *Node {
 	}
 
 	if inlMap[fn] {
-		if Debug['m'] > 1 {
+		if Debug.m > 1 {
 			fmt.Printf("%v: cannot inline %v into %v: repeated recursive cycle\n", n.Line(), fn, Curfn.funcname())
 		}
 		return n
@@ -925,12 +925,12 @@ func mkinlcall(n, fn *Node, maxCost int32, inlMap map[*Node]bool) *Node {
 	}
 
 	// We have a function node, and it has an inlineable body.
-	if Debug['m'] > 1 {
+	if Debug.m > 1 {
 		fmt.Printf("%v: inlining call to %v %#v { %#v }\n", n.Line(), fn.Sym, fn.Type, asNodes(fn.Func.Inl.Body))
-	} else if Debug['m'] != 0 {
+	} else if Debug.m != 0 {
 		fmt.Printf("%v: inlining call to %v\n", n.Line(), fn)
 	}
-	if Debug['m'] > 2 {
+	if Debug.m > 2 {
 		fmt.Printf("%v: Before inlining: %+v\n", n.Line(), n)
 	}
 
@@ -1174,7 +1174,7 @@ func mkinlcall(n, fn *Node, maxCost int32, inlMap map[*Node]bool) *Node {
 		}
 	}
 
-	if Debug['m'] > 2 {
+	if Debug.m > 2 {
 		fmt.Printf("%v: After inlining %+v\n\n", call.Line(), call)
 	}
 
@@ -1185,7 +1185,7 @@ func mkinlcall(n, fn *Node, maxCost int32, inlMap map[*Node]bool) *Node {
 // PAUTO's in the calling functions, and link them off of the
 // PPARAM's, PAUTOS and PPARAMOUTs of the called function.
 func inlvar(var_ *Node) *Node {
-	if Debug['m'] > 3 {
+	if Debug.m > 3 {
 		fmt.Printf("inlvar %+v\n", var_)
 	}
 
@@ -1264,13 +1264,13 @@ func (subst *inlsubst) node(n *Node) *Node {
 	switch n.Op {
 	case ONAME:
 		if inlvar := subst.inlvars[n]; inlvar != nil { // These will be set during inlnode
-			if Debug['m'] > 2 {
+			if Debug.m > 2 {
 				fmt.Printf("substituting name %+v  ->  %+v\n", n, inlvar)
 			}
 			return inlvar
 		}
 
-		if Debug['m'] > 2 {
+		if Debug.m > 2 {
 			fmt.Printf("not substituting name %+v\n", n)
 		}
 		return n
diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index 2fffe625cd..949755a0e2 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -211,18 +211,27 @@ func Main(archInit func(*Arch)) {
 
 	flag.BoolVar(&compiling_runtime, "+", false, "compiling runtime")
 	flag.BoolVar(&compiling_std, "std", false, "compiling standard library")
-	objabi.Flagcount("%", "debug non-static initializers", &Debug['%'])
-	objabi.Flagcount("B", "disable bounds checking", &Debug['B'])
-	objabi.Flagcount("C", "disable printing of columns in error messages", &Debug['C']) // TODO(gri) remove eventually
 	flag.StringVar(&localimport, "D", "", "set relative `path` for local imports")
-	objabi.Flagcount("E", "debug symbol export", &Debug['E'])
+
+	objabi.Flagcount("%", "debug non-static initializers", &Debug.P)
+	objabi.Flagcount("B", "disable bounds checking", &Debug.B)
+	objabi.Flagcount("C", "disable printing of columns in error messages", &Debug.C)
+	objabi.Flagcount("E", "debug symbol export", &Debug.E)
+	objabi.Flagcount("K", "debug missing line numbers", &Debug.K)
+	objabi.Flagcount("L", "show full file names in error messages", &Debug.L)
+	objabi.Flagcount("N", "disable optimizations", &Debug.N)
+	objabi.Flagcount("S", "print assembly listing", &Debug.S)
+	objabi.Flagcount("W", "debug parse tree after type checking", &Debug.W)
+	objabi.Flagcount("e", "no limit on number of errors reported", &Debug.e)
+	objabi.Flagcount("h", "halt on error", &Debug.h)
+	objabi.Flagcount("j", "debug runtime-initialized variables", &Debug.j)
+	objabi.Flagcount("l", "disable inlining", &Debug.l)
+	objabi.Flagcount("m", "print optimization decisions", &Debug.m)
+	objabi.Flagcount("r", "debug generated wrappers", &Debug.r)
+	objabi.Flagcount("w", "debug type checking", &Debug.w)
+
 	objabi.Flagfn1("I", "add `directory` to import search path", addidir)
-	objabi.Flagcount("K", "debug missing line numbers", &Debug['K'])
-	objabi.Flagcount("L", "show full file names in error messages", &Debug['L'])
-	objabi.Flagcount("N", "disable optimizations", &Debug['N'])
-	objabi.Flagcount("S", "print assembly listing", &Debug['S'])
 	objabi.AddVersionFlag() // -V
-	objabi.Flagcount("W", "debug parse tree after type checking", &Debug['W'])
 	flag.StringVar(&asmhdr, "asmhdr", "", "write assembly header to `file`")
 	flag.StringVar(&buildid, "buildid", "", "record `id` as the build id in the export metadata")
 	flag.IntVar(&nBackendWorkers, "c", 1, "concurrency during compilation, 1 means no concurrency")
@@ -231,17 +240,12 @@ func Main(archInit func(*Arch)) {
 	flag.BoolVar(&flagDWARF, "dwarf", !Wasm, "generate DWARF symbols")
 	flag.BoolVar(&Ctxt.Flag_locationlists, "dwarflocationlists", true, "add location lists to DWARF in optimized mode")
 	flag.IntVar(&genDwarfInline, "gendwarfinl", 2, "generate DWARF inline info records")
-	objabi.Flagcount("e", "no limit on number of errors reported", &Debug['e'])
-	objabi.Flagcount("h", "halt on error", &Debug['h'])
 	objabi.Flagfn1("importmap", "add `definition` of the form source=actual to import map", addImportMap)
 	objabi.Flagfn1("importcfg", "read import configuration from `file`", readImportCfg)
 	flag.StringVar(&flag_installsuffix, "installsuffix", "", "set pkg directory `suffix`")
-	objabi.Flagcount("j", "debug runtime-initialized variables", &Debug['j'])
-	objabi.Flagcount("l", "disable inlining", &Debug['l'])
 	flag.StringVar(&flag_lang, "lang", "", "release to compile for")
 	flag.StringVar(&linkobj, "linkobj", "", "write linker-specific object to `file`")
 	objabi.Flagcount("live", "debug liveness analysis", &debuglive)
-	objabi.Flagcount("m", "print optimization decisions", &Debug['m'])
 	if sys.MSanSupported(objabi.GOOS, objabi.GOARCH) {
 		flag.BoolVar(&flag_msan, "msan", false, "build code compatible with C/C++ memory sanitizer")
 	}
@@ -249,7 +253,6 @@ func Main(archInit func(*Arch)) {
 	flag.StringVar(&outfile, "o", "", "write output to `file`")
 	flag.StringVar(&myimportpath, "p", "", "set expected package import `path`")
 	flag.BoolVar(&writearchive, "pack", false, "write to file.a instead of file.o")
-	objabi.Flagcount("r", "debug generated wrappers", &Debug['r'])
 	if sys.RaceDetectorSupported(objabi.GOOS, objabi.GOARCH) {
 		flag.BoolVar(&flag_race, "race", false, "enable race detector")
 	}
@@ -259,7 +262,6 @@ func Main(archInit func(*Arch)) {
 	}
 	flag.StringVar(&pathPrefix, "trimpath", "", "remove `prefix` from recorded source file paths")
 	flag.BoolVar(&Debug_vlog, "v", false, "increase debug verbosity")
-	objabi.Flagcount("w", "debug type checking", &Debug['w'])
 	flag.BoolVar(&use_writebarrier, "wb", true, "enable write barrier")
 	var flag_shared bool
 	var flag_dynlink bool
@@ -325,9 +327,9 @@ func Main(archInit func(*Arch)) {
 
 	Ctxt.Flag_shared = flag_dynlink || flag_shared
 	Ctxt.Flag_dynlink = flag_dynlink
-	Ctxt.Flag_optimize = Debug['N'] == 0
+	Ctxt.Flag_optimize = Debug.N == 0
 
-	Ctxt.Debugasm = Debug['S']
+	Ctxt.Debugasm = Debug.S
 	Ctxt.Debugvlog = Debug_vlog
 	if flagDWARF {
 		Ctxt.DebugInfo = debuginfo
@@ -399,7 +401,7 @@ func Main(archInit func(*Arch)) {
 		instrumenting = true
 	}
 
-	if compiling_runtime && Debug['N'] != 0 {
+	if compiling_runtime && Debug.N != 0 {
 		log.Fatal("cannot disable optimizations while compiling runtime")
 	}
 	if nBackendWorkers < 1 {
@@ -504,11 +506,11 @@ func Main(archInit func(*Arch)) {
 	}
 
 	// enable inlining.  for now:
-	//	default: inlining on.  (debug['l'] == 1)
-	//	-l: inlining off  (debug['l'] == 0)
-	//	-l=2, -l=3: inlining on again, with extra debugging (debug['l'] > 1)
-	if Debug['l'] <= 1 {
-		Debug['l'] = 1 - Debug['l']
+	//	default: inlining on.  (Debug.l == 1)
+	//	-l: inlining off  (Debug.l == 0)
+	//	-l=2, -l=3: inlining on again, with extra debugging (Debug.l > 1)
+	if Debug.l <= 1 {
+		Debug.l = 1 - Debug.l
 	}
 
 	if jsonLogOpt != "" { // parse version,destination from json logging optimization.
@@ -666,7 +668,7 @@ func Main(archInit func(*Arch)) {
 	// Phase 5: Inlining
 	timings.Start("fe", "inlining")
 	if Debug_typecheckinl != 0 {
-		// Typecheck imported function bodies if debug['l'] > 1,
+		// Typecheck imported function bodies if Debug.l > 1,
 		// otherwise lazily when used or re-exported.
 		for _, n := range importlist {
 			if n.Func.Inl != nil {
@@ -680,7 +682,7 @@ func Main(archInit func(*Arch)) {
 		}
 	}
 
-	if Debug['l'] != 0 {
+	if Debug.l != 0 {
 		// Find functions that can be inlined and clone them before walk expands them.
 		visitBottomUp(xtop, func(list []*Node, recursive bool) {
 			numfns := numNonClosures(list)
@@ -691,7 +693,7 @@ func Main(archInit func(*Arch)) {
 					// across more than one function.
 					caninl(n)
 				} else {
-					if Debug['m'] > 1 {
+					if Debug.m > 1 {
 						fmt.Printf("%v: cannot inline %v: recursive\n", n.Line(), n.Func.Nname)
 					}
 				}
@@ -1408,29 +1410,34 @@ func IsAlias(sym *types.Sym) bool {
 	return sym.Def != nil && asNode(sym.Def).Sym != sym
 }
 
-// By default, assume any debug flags are incompatible with concurrent compilation.
-// A few are safe and potentially in common use for normal compiles, though; mark them as such here.
-var concurrentFlagOK = [256]bool{
-	'B': true, // disabled bounds checking
-	'C': true, // disable printing of columns in error messages
-	'e': true, // no limit on errors; errors all come from non-concurrent code
-	'I': true, // add `directory` to import search path
-	'N': true, // disable optimizations
-	'l': true, // disable inlining
-	'w': true, // all printing happens before compilation
-	'W': true, // all printing happens before compilation
-	'S': true, // printing disassembly happens at the end (but see concurrentBackendAllowed below)
+// By default, assume any debug flags are incompatible with concurrent
+// compilation. A few are safe and potentially in common use for
+// normal compiles, though; return true for those.
+func concurrentFlagOk() bool {
+	// Report whether any debug flag that would prevent concurrent
+	// compilation is set, by zeroing out the allowed ones and then
+	// checking if the resulting struct is zero.
+	d := Debug
+	d.B = 0 // disable bounds checking
+	d.C = 0 // disable printing of columns in error messages
+	d.e = 0 // no limit on errors; errors all come from non-concurrent code
+	d.N = 0 // disable optimizations
+	d.l = 0 // disable inlining
+	d.w = 0 // all printing happens before compilation
+	d.W = 0 // all printing happens before compilation
+	d.S = 0 // printing disassembly happens at the end (but see concurrentBackendAllowed below)
+
+	return d == DebugFlags{}
 }
 
 func concurrentBackendAllowed() bool {
-	for i, x := range &Debug {
-		if x != 0 && !concurrentFlagOK[i] {
-			return false
-		}
+	if !concurrentFlagOk() {
+		return false
 	}
-	// Debug['S'] by itself is ok, because all printing occurs
+
+	// Debug.S by itself is ok, because all printing occurs
 	// while writing the object file, and that is non-concurrent.
-	// Adding Debug_vlog, however, causes Debug['S'] to also print
+	// Adding Debug_vlog, however, causes Debug.S to also print
 	// while flushing the plist, which happens concurrently.
 	if Debug_vlog || debugstr != "" || debuglive > 0 {
 		return false
diff --git a/src/cmd/compile/internal/gc/order.go b/src/cmd/compile/internal/gc/order.go
index e562ab7556..f7fe3ed360 100644
--- a/src/cmd/compile/internal/gc/order.go
+++ b/src/cmd/compile/internal/gc/order.go
@@ -50,7 +50,7 @@ type Order struct {
 // Order rewrites fn.Nbody to apply the ordering constraints
 // described in the comment at the top of the file.
 func order(fn *Node) {
-	if Debug['W'] > 1 {
+	if Debug.W > 1 {
 		s := fmt.Sprintf("\nbefore order %v", fn.Func.Nname.Sym)
 		dumplist(s, fn.Nbody)
 	}
@@ -328,7 +328,7 @@ func orderMakeSliceCopy(s []*Node) {
 		return
 	}
 
-	if Debug['N'] != 0 || instrumenting {
+	if Debug.N != 0 || instrumenting {
 		return
 	}
 
diff --git a/src/cmd/compile/internal/gc/range.go b/src/cmd/compile/internal/gc/range.go
index 6d22964dcd..1b4d765d42 100644
--- a/src/cmd/compile/internal/gc/range.go
+++ b/src/cmd/compile/internal/gc/range.go
@@ -466,7 +466,7 @@ func walkrange(n *Node) *Node {
 //
 // where == for keys of map m is reflexive.
 func isMapClear(n *Node) bool {
-	if Debug['N'] != 0 || instrumenting {
+	if Debug.N != 0 || instrumenting {
 		return false
 	}
 
@@ -533,7 +533,7 @@ func mapClear(m *Node) *Node {
 //
 // Parameters are as in walkrange: "for v1, v2 = range a".
 func arrayClear(n, v1, v2, a *Node) bool {
-	if Debug['N'] != 0 || instrumenting {
+	if Debug.N != 0 || instrumenting {
 		return false
 	}
 
diff --git a/src/cmd/compile/internal/gc/sinit.go b/src/cmd/compile/internal/gc/sinit.go
index fda33534b6..9c4dcd739c 100644
--- a/src/cmd/compile/internal/gc/sinit.go
+++ b/src/cmd/compile/internal/gc/sinit.go
@@ -39,7 +39,7 @@ func (s *InitSchedule) append(n *Node) {
 // staticInit adds an initialization statement n to the schedule.
 func (s *InitSchedule) staticInit(n *Node) {
 	if !s.tryStaticInit(n) {
-		if Debug['%'] != 0 {
+		if Debug.P != 0 {
 			Dump("nonstatic", n)
 		}
 		s.append(n)
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index e1455d2c3f..65beb84911 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -59,7 +59,7 @@ func initssaconfig() {
 	_ = types.NewPtr(types.Types[TINT64])                             // *int64
 	_ = types.NewPtr(types.Errortype)                                 // *error
 	types.NewPtrCacheEnabled = false
-	ssaConfig = ssa.NewConfig(thearch.LinkArch.Name, *types_, Ctxt, Debug['N'] == 0)
+	ssaConfig = ssa.NewConfig(thearch.LinkArch.Name, *types_, Ctxt, Debug.N == 0)
 	ssaConfig.SoftFloat = thearch.SoftFloat
 	ssaConfig.Race = flag_race
 	ssaCaches = make([]ssa.Cache, nBackendWorkers)
@@ -357,7 +357,7 @@ func buildssa(fn *Node, worker int) *ssa.Func {
 	s.fwdVars = map[*Node]*ssa.Value{}
 	s.startmem = s.entryNewValue0(ssa.OpInitMem, types.TypeMem)
 
-	s.hasOpenDefers = Debug['N'] == 0 && s.hasdefer && !s.curfn.Func.OpenCodedDeferDisallowed()
+	s.hasOpenDefers = Debug.N == 0 && s.hasdefer && !s.curfn.Func.OpenCodedDeferDisallowed()
 	switch {
 	case s.hasOpenDefers && (Ctxt.Flag_shared || Ctxt.Flag_dynlink) && thearch.LinkArch.Name == "386":
 		// Don't support open-coded defers for 386 ONLY when using shared
@@ -741,7 +741,7 @@ func (s *state) pushLine(line src.XPos) {
 		// the frontend may emit node with line number missing,
 		// use the parent line number in this case.
 		line = s.peekPos()
-		if Debug['K'] != 0 {
+		if Debug.K != 0 {
 			Warn("buildssa: unknown position (line 0)")
 		}
 	} else {
@@ -1214,7 +1214,7 @@ func (s *state) stmt(n *Node) {
 				// Check whether we're writing the result of an append back to the same slice.
 				// If so, we handle it specially to avoid write barriers on the fast
 				// (non-growth) path.
-				if !samesafeexpr(n.Left, rhs.List.First()) || Debug['N'] != 0 {
+				if !samesafeexpr(n.Left, rhs.List.First()) || Debug.N != 0 {
 					break
 				}
 				// If the slice can be SSA'd, it'll be on the stack,
@@ -4849,7 +4849,7 @@ func (s *state) addr(n *Node) *ssa.Value {
 // canSSA reports whether n is SSA-able.
 // n must be an ONAME (or an ODOT sequence with an ONAME base).
 func (s *state) canSSA(n *Node) bool {
-	if Debug['N'] != 0 {
+	if Debug.N != 0 {
 		return false
 	}
 	for n.Op == ODOT || (n.Op == OINDEX && n.Left.Type.IsArray()) {
@@ -4960,7 +4960,7 @@ func (s *state) nilCheck(ptr *ssa.Value) {
 func (s *state) boundsCheck(idx, len *ssa.Value, kind ssa.BoundsKind, bounded bool) *ssa.Value {
 	idx = s.extendIndex(idx, len, kind, bounded)
 
-	if bounded || Debug['B'] != 0 {
+	if bounded || Debug.B != 0 {
 		// If bounded or bounds checking is flag-disabled, then no check necessary,
 		// just return the extended index.
 		//
@@ -6310,7 +6310,7 @@ func genssa(f *ssa.Func, pp *Progs) {
 		}
 		// Emit control flow instructions for block
 		var next *ssa.Block
-		if i < len(f.Blocks)-1 && Debug['N'] == 0 {
+		if i < len(f.Blocks)-1 && Debug.N == 0 {
 			// If -N, leave next==nil so every block with successors
 			// ends in a JMP (except call blocks - plive doesn't like
 			// select{send,recv} followed by a JMP call).  Helps keep
@@ -6618,7 +6618,7 @@ func (s *state) extendIndex(idx, len *ssa.Value, kind ssa.BoundsKind, bounded bo
 		} else {
 			lo = s.newValue1(ssa.OpInt64Lo, types.Types[TUINT], idx)
 		}
-		if bounded || Debug['B'] != 0 {
+		if bounded || Debug.B != 0 {
 			return lo
 		}
 		bNext := s.f.NewBlock(ssa.BlockPlain)
diff --git a/src/cmd/compile/internal/gc/subr.go b/src/cmd/compile/internal/gc/subr.go
index b6e6f3a6da..eccd6f8a74 100644
--- a/src/cmd/compile/internal/gc/subr.go
+++ b/src/cmd/compile/internal/gc/subr.go
@@ -96,7 +96,7 @@ func flusherrors() {
 }
 
 func hcrash() {
-	if Debug['h'] != 0 {
+	if Debug.h != 0 {
 		flusherrors()
 		if outfile != "" {
 			os.Remove(outfile)
@@ -107,7 +107,7 @@ func hcrash() {
 }
 
 func linestr(pos src.XPos) string {
-	return Ctxt.OutermostPos(pos).Format(Debug['C'] == 0, Debug['L'] == 1)
+	return Ctxt.OutermostPos(pos).Format(Debug.C == 0, Debug.L == 1)
 }
 
 // lasterror keeps track of the most recently issued error.
@@ -153,7 +153,7 @@ func yyerrorl(pos src.XPos, format string, args ...interface{}) {
 
 	hcrash()
 	nerrors++
-	if nsavederrors+nerrors >= 10 && Debug['e'] == 0 {
+	if nsavederrors+nerrors >= 10 && Debug.e == 0 {
 		flusherrors()
 		fmt.Printf("%v: too many errors\n", linestr(pos))
 		errorexit()
@@ -175,7 +175,7 @@ func Warn(fmt_ string, args ...interface{}) {
 
 func Warnl(line src.XPos, fmt_ string, args ...interface{}) {
 	adderr(line, fmt_, args...)
-	if Debug['m'] != 0 {
+	if Debug.m != 0 {
 		flusherrors()
 	}
 }
@@ -222,7 +222,7 @@ func hasUniquePos(n *Node) bool {
 	}
 
 	if !n.Pos.IsKnown() {
-		if Debug['K'] != 0 {
+		if Debug.K != 0 {
 			Warn("setlineno: unknown position (line 0)")
 		}
 		return false
@@ -1506,7 +1506,7 @@ func structargs(tl *types.Type, mustname bool) []*Node {
 //	method - M func (t T)(), a TFIELD type struct
 //	newnam - the eventual mangled name of this function
 func genwrapper(rcvr *types.Type, method *types.Field, newnam *types.Sym) {
-	if false && Debug['r'] != 0 {
+	if false && Debug.r != 0 {
 		fmt.Printf("genwrapper rcvrtype=%v method=%v newnam=%v\n", rcvr, method, newnam)
 	}
 
@@ -1579,7 +1579,7 @@ func genwrapper(rcvr *types.Type, method *types.Field, newnam *types.Sym) {
 		fn.Nbody.Append(call)
 	}
 
-	if false && Debug['r'] != 0 {
+	if false && Debug.r != 0 {
 		dumplist("genwrapper body", fn.Nbody)
 	}
 
@@ -1720,7 +1720,7 @@ func implements(t, iface *types.Type, m, samename **types.Field, ptr *int) bool
 		// the method does not exist for value types.
 		rcvr := tm.Type.Recv().Type
 		if rcvr.IsPtr() && !t0.IsPtr() && !followptr && !isifacemethod(tm.Type) {
-			if false && Debug['r'] != 0 {
+			if false && Debug.r != 0 {
 				yyerror("interface pointer mismatch")
 			}
 
diff --git a/src/cmd/compile/internal/gc/syntax.go b/src/cmd/compile/internal/gc/syntax.go
index a2ab0fa661..e3b4963977 100644
--- a/src/cmd/compile/internal/gc/syntax.go
+++ b/src/cmd/compile/internal/gc/syntax.go
@@ -247,7 +247,7 @@ func (n *Node) Val() Val {
 // SetVal sets the Val for the node, which must not have been used with SetOpt.
 func (n *Node) SetVal(v Val) {
 	if n.HasOpt() {
-		Debug['h'] = 1
+		Debug.h = 1
 		Dump("have Opt", n)
 		Fatalf("have Opt")
 	}
@@ -270,7 +270,7 @@ func (n *Node) SetOpt(x interface{}) {
 		return
 	}
 	if n.HasVal() {
-		Debug['h'] = 1
+		Debug.h = 1
 		Dump("have Val", n)
 		Fatalf("have Val")
 	}
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 9df288ea65..6ce3eda44b 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -21,7 +21,7 @@ const zeroValSize = 1024 // must match value of runtime/map.go:maxZero
 func walk(fn *Node) {
 	Curfn = fn
 
-	if Debug['W'] != 0 {
+	if Debug.W != 0 {
 		s := fmt.Sprintf("\nbefore walk %v", Curfn.Func.Nname.Sym)
 		dumplist(s, Curfn.Nbody)
 	}
@@ -63,14 +63,14 @@ func walk(fn *Node) {
 		return
 	}
 	walkstmtlist(Curfn.Nbody.Slice())
-	if Debug['W'] != 0 {
+	if Debug.W != 0 {
 		s := fmt.Sprintf("after walk %v", Curfn.Func.Nname.Sym)
 		dumplist(s, Curfn.Nbody)
 	}
 
 	zeroResults()
 	heapmoves()
-	if Debug['W'] != 0 && Curfn.Func.Enter.Len() > 0 {
+	if Debug.W != 0 && Curfn.Func.Enter.Len() > 0 {
 		s := fmt.Sprintf("enter %v", Curfn.Func.Nname.Sym)
 		dumplist(s, Curfn.Func.Enter)
 	}
@@ -436,7 +436,7 @@ func walkexpr(n *Node, init *Nodes) *Node {
 
 	lno := setlineno(n)
 
-	if Debug['w'] > 1 {
+	if Debug.w > 1 {
 		Dump("before walk expr", n)
 	}
 
@@ -1049,7 +1049,7 @@ opswitch:
 		}
 		if t.IsArray() {
 			n.SetBounded(bounded(r, t.NumElem()))
-			if Debug['m'] != 0 && n.Bounded() && !Isconst(n.Right, CTINT) {
+			if Debug.m != 0 && n.Bounded() && !Isconst(n.Right, CTINT) {
 				Warn("index bounds check elided")
 			}
 			if smallintconst(n.Right) && !n.Bounded() {
@@ -1057,7 +1057,7 @@ opswitch:
 			}
 		} else if Isconst(n.Left, CTSTR) {
 			n.SetBounded(bounded(r, int64(len(n.Left.StringVal()))))
-			if Debug['m'] != 0 && n.Bounded() && !Isconst(n.Right, CTINT) {
+			if Debug.m != 0 && n.Bounded() && !Isconst(n.Right, CTINT) {
 				Warn("index bounds check elided")
 			}
 			if smallintconst(n.Right) && !n.Bounded() {
@@ -1599,7 +1599,7 @@ opswitch:
 
 	updateHasCall(n)
 
-	if Debug['w'] != 0 && n != nil {
+	if Debug.w != 0 && n != nil {
 		Dump("after walk expr", n)
 	}
 
@@ -2819,7 +2819,7 @@ func appendslice(n *Node, init *Nodes) *Node {
 // isAppendOfMake reports whether n is of the form append(x , make([]T, y)...).
 // isAppendOfMake assumes n has already been typechecked.
 func isAppendOfMake(n *Node) bool {
-	if Debug['N'] != 0 || instrumenting {
+	if Debug.N != 0 || instrumenting {
 		return false
 	}
 
@@ -3976,7 +3976,7 @@ func canMergeLoads() bool {
 // isRuneCount reports whether n is of the form len([]rune(string)).
 // These are optimized into a call to runtime.countrunes.
 func isRuneCount(n *Node) bool {
-	return Debug['N'] == 0 && !instrumenting && n.Op == OLEN && n.Left.Op == OSTR2RUNES
+	return Debug.N == 0 && !instrumenting && n.Op == OLEN && n.Left.Op == OSTR2RUNES
 }
 
 func walkCheckPtrAlignment(n *Node, init *Nodes, count *Node) *Node {