cmd/compile: deprecate derived info needed field

This field is unused since shape-based stenciling was added for Unified
IR (CL 421821). The derived types information is now explicitly using
derived-type dictionaries (CL 331829).

This CL follows the pattern used in CL 606035.

Updates #68778

Change-Id: Ie784b6443c0a651854bfbcebb8a5166b1481408b
Reviewed-on: https://go-review.googlesource.com/c/go/+/608216
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Tim King <taking@google.com>

src/cmd/compile/internal/importer/ureader.go

@@ -483,7 +483,10 @@ func (pr *pkgReader) objDictIdx(idx pkgbits.Index) *readerDict {
 		dict.derived = make([]derivedInfo, r.Len())
 		dict.derivedTypes = make([]types2.Type, len(dict.derived))
 		for i := range dict.derived {
-			dict.derived[i] = derivedInfo{r.Reloc(pkgbits.RelocType), r.Bool()}
+			dict.derived[i] = derivedInfo{idx: r.Reloc(pkgbits.RelocType)}
+			if r.Version().Has(pkgbits.DerivedInfoNeeded) {
+				assert(!r.Bool())
+			}
 		}
 
 		pr.retireReader(r)

src/cmd/compile/internal/noder/reader.go

@@ -984,7 +984,10 @@ func (pr *pkgReader) objDictIdx(sym *types.Sym, idx index, implicits, explicits
 	dict.derived = make([]derivedInfo, r.Len())
 	dict.derivedTypes = make([]*types.Type, len(dict.derived))
 	for i := range dict.derived {
-		dict.derived[i] = derivedInfo{r.Reloc(pkgbits.RelocType), r.Bool()}
+		dict.derived[i] = derivedInfo{idx: r.Reloc(pkgbits.RelocType)}
+		if r.Version().Has(pkgbits.DerivedInfoNeeded) {
+			assert(!r.Bool())
+		}
 	}
 
 	// Runtime dictionary information; private to the compiler.

src/cmd/compile/internal/noder/writer.go

@@ -236,8 +236,7 @@ func (dict *writerDict) typeParamIndex(typ *types2.TypeParam) int {
 
 // A derivedInfo represents a reference to an encoded generic Go type.
 type derivedInfo struct {
-	idx    index
-	needed bool // TODO(mdempsky): Remove.
+	idx index
 }
 
 // A typeInfo represents a reference to an encoded Go type.
@@ -915,7 +914,9 @@ func (w *writer) objDict(obj types2.Object, dict *writerDict) {
 	w.Len(nderived)
 	for _, typ := range dict.derived {
 		w.Reloc(pkgbits.RelocType, typ.idx)
-		w.Bool(typ.needed)
+		if w.Version().Has(pkgbits.DerivedInfoNeeded) {
+			w.Bool(false)
+		}
 	}
 
 	// Write runtime dictionary information.

src/go/internal/gcimporter/ureader.go

@@ -575,7 +575,10 @@ func (pr *pkgReader) objDictIdx(idx pkgbits.Index) *readerDict {
 		dict.derived = make([]derivedInfo, r.Len())
 		dict.derivedTypes = make([]types.Type, len(dict.derived))
 		for i := range dict.derived {
-			dict.derived[i] = derivedInfo{r.Reloc(pkgbits.RelocType), r.Bool()}
+			dict.derived[i] = derivedInfo{idx: r.Reloc(pkgbits.RelocType)}
+			if r.Version().Has(pkgbits.DerivedInfoNeeded) {
+				assert(!r.Bool())
+			}
 		}
 
 		pr.retireReader(r)