cmd/compile: drop internal range-over-func vars from DWARF output

Drops internal range-over-func variables from the DWARF output
(excluding #yield which is used by Delve).

Fixes #68238

Change-Id: Ic035e37ca3560347276cdc3b469fd564da33f4f5
Reviewed-on: https://go-review.googlesource.com/c/go/+/594257
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Auto-Submit: Hyang-Ah Hana Kim <hyangah@gmail.com>

src/cmd/compile/internal/dwarfgen/dwarf.go

@@ -91,6 +91,9 @@ func Info(fnsym *obj.LSym, infosym *obj.LSym, curfn obj.Func) (scopes []dwarf.Sc
 			default:
 				continue
 			}
+			if !ssa.IsVarWantedForDebug(n) {
+				continue
+			}
 			apdecls = append(apdecls, n)
 			if n.Type().Kind() == types.TSSA {
 				// Can happen for TypeInt128 types. This only happens for
@@ -194,6 +197,9 @@ func createDwarfVars(fnsym *obj.LSym, complexOK bool, fn *ir.Func, apDecls []*ir
 		// DWARF-gen. See issue 48573 for more details.
 		debugInfo := fn.DebugInfo.(*ssa.FuncDebug)
 		for _, n := range debugInfo.RegOutputParams {
+			if !ssa.IsVarWantedForDebug(n) {
+				continue
+			}
 			if n.Class != ir.PPARAMOUT || !n.IsOutputParamInRegisters() {
 				panic("invalid ir.Name on debugInfo.RegOutputParams list")
 			}

src/cmd/compile/internal/rangefunc/rewrite.go

@@ -1137,7 +1137,7 @@ func (r *rewriter) setStateAt(index int, stateVal abi.RF_State) *syntax.AssignSt
 func (r *rewriter) bodyFunc(body []syntax.Stmt, lhs []syntax.Expr, def bool, ftyp *types2.Signature, start, end syntax.Pos) *syntax.FuncLit {
 	// Starting X(bodyFunc); build up bodyFunc first.
 	var params, results []*types2.Var
-	results = append(results, types2.NewVar(start, nil, "", r.bool.Type()))
+	results = append(results, types2.NewVar(start, nil, "#r", r.bool.Type()))
 	bodyFunc := &syntax.FuncLit{
 		// Note: Type is ignored but needs to be non-nil to avoid panic in syntax.Inspect.
 		Type: &syntax.FuncType{},

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

@@ -600,7 +600,7 @@ func BuildFuncDebug(ctxt *obj.Link, f *Func, loggingLevel int, stackOffset func(
 	state.vars = state.vars[:0]
 	for i, slot := range f.Names {
 		state.slots = append(state.slots, *slot)
-		if ir.IsSynthetic(slot.N) {
+		if ir.IsSynthetic(slot.N) || !IsVarWantedForDebug(slot.N) {
 			continue
 		}
 
@@ -620,7 +620,7 @@ func BuildFuncDebug(ctxt *obj.Link, f *Func, loggingLevel int, stackOffset func(
 		for _, v := range b.Values {
 			if v.Op == OpVarDef {
 				n := v.Aux.(*ir.Name)
-				if ir.IsSynthetic(n) {
+				if ir.IsSynthetic(n) || !IsVarWantedForDebug(n) {
 					continue
 				}
 
@@ -665,7 +665,7 @@ func BuildFuncDebug(ctxt *obj.Link, f *Func, loggingLevel int, stackOffset func(
 	state.initializeCache(f, len(state.varParts), len(state.slots))
 
 	for i, slot := range f.Names {
-		if ir.IsSynthetic(slot.N) {
+		if ir.IsSynthetic(slot.N) || !IsVarWantedForDebug(slot.N) {
 			continue
 		}
 		for _, value := range f.NamedValues[*slot] {
@@ -1087,7 +1087,7 @@ func (state *debugState) processValue(v *Value, vSlots []SlotID, vReg *Register)
 	switch {
 	case v.Op == OpVarDef:
 		n := v.Aux.(*ir.Name)
-		if ir.IsSynthetic(n) {
+		if ir.IsSynthetic(n) || !IsVarWantedForDebug(n) {
 			break
 		}
 
@@ -1835,6 +1835,9 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 			// will be sorted out elsewhere
 			continue
 		}
+		if !IsVarWantedForDebug(inp.Name) {
+			continue
+		}
 		addVarSlot(inp.Name, inp.Type)
 		params = append(params, inp)
 	}
@@ -1855,6 +1858,9 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 			// will be sorted out elsewhere
 			continue
 		}
+		if !IsVarWantedForDebug(inp.Name) {
+			continue
+		}
 
 		sl := rval.Slots[pidx]
 		n := rval.Vars[pidx]
@@ -1948,3 +1954,19 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 		pidx++
 	}
 }
+
+// IsVarWantedForDebug returns true if the debug info for the node should
+// be generated.
+// For example, internal variables for range-over-func loops have little
+// value to users, so we don't generate debug info for them.
+func IsVarWantedForDebug(n ir.Node) bool {
+	name := n.Sym().Name
+	if len(name) > 0 && name[0] == '&' {
+		name = name[1:]
+	}
+	if len(name) > 0 && name[0] == '#' {
+		// #yield is used by delve.
+		return strings.HasPrefix(name, "#yield")
+	}
+	return true
+}