cmd/compile/internal/noder: set ir.Name.DictIndex for unified IR

For local variables of derived type, Delve relies on ir.Name.DictIndex
being set to the type's rtype index within the function's dictionary.
This CL implements that functionality within unified IR.

Manually double checked that Delve behaves correctly, at least as far
as I can tell from casual use. Specifically, I confirmed that running
the test program from TestDictIndex, stepping into testfn, and then
running `print mapvar` prints `map[int]main.CustomInt []`, which
matches the behavior under GOEXPERIMENT=nounified. (Also compare that
when ir.Name.DictIndex is *not* set by unified IR, `print mapvar`
instead prints `map[int]go.shape.int []`.)

Fixes #54514.

Change-Id: I90d443945895abfba04dc018f15e00217930091c
Reviewed-on: https://go-review.googlesource.com/c/go/+/424735
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

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

@@ -1490,7 +1490,7 @@ func (r *reader) addLocal(name *ir.Name, ctxt ir.Class) {
 	if name.Sym().Name == dictParamName {
 		r.dictParam = name
 	} else {
-		if ctxt == ir.PAUTO {
+		if r.synthetic == nil {
 			r.Sync(pkgbits.SyncAddLocal)
 			if r.p.SyncMarkers() {
 				want := r.Int()
@@ -1498,12 +1498,10 @@ func (r *reader) addLocal(name *ir.Name, ctxt ir.Class) {
 					base.FatalfAt(name.Pos(), "locals table has desynced")
 				}
 			}
+			r.varDictIndex(name)
 		}
 
 		r.locals = append(r.locals, name)
-
-		// TODO(go.dev/issue/54514): Set name.DictIndex for variables of
-		// derived type and enable cmd/link/internal/ld.TestDictIndex.
 	}
 
 	name.SetUsed(true)
@@ -3062,6 +3060,17 @@ func (r *reader) rtype0(pos src.XPos) (typ *types.Type, rtype ir.Node) {
 	return
 }
 
+// varDictIndex populates name.DictIndex if name is a derived type.
+func (r *reader) varDictIndex(name *ir.Name) {
+	if r.Bool() {
+		idx := 1 + r.dict.rtypesOffset() + r.Len()
+		if int(uint16(idx)) != idx {
+			base.FatalfAt(name.Pos(), "DictIndex overflow for %v: %v", name, idx)
+		}
+		name.DictIndex = uint16(idx)
+	}
+}
+
 func (r *reader) itab(pos src.XPos) (typ *types.Type, typRType ir.Node, iface *types.Type, ifaceRType ir.Node, itab ir.Node) {
 	if r.Bool() { // derived types
 		idx := r.Len()

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

@@ -1090,20 +1090,19 @@ func (w *writer) funcargs(sig *types2.Signature) {
 
 func (w *writer) funcarg(param *types2.Var, result bool) {
 	if param.Name() != "" || result {
-		w.addLocal(param, true)
+		w.addLocal(param)
 	}
 }
 
 // addLocal records the declaration of a new local variable.
-func (w *writer) addLocal(obj *types2.Var, isParam bool) {
+func (w *writer) addLocal(obj *types2.Var) {
 	idx := len(w.localsIdx)
 
-	if !isParam {
-		w.Sync(pkgbits.SyncAddLocal)
-		if w.p.SyncMarkers() {
-			w.Int(idx)
-		}
+	w.Sync(pkgbits.SyncAddLocal)
+	if w.p.SyncMarkers() {
+		w.Int(idx)
 	}
+	w.varDictIndex(obj)
 
 	if w.localsIdx == nil {
 		w.localsIdx = make(map[*types2.Var]int)
@@ -1295,7 +1294,7 @@ func (w *writer) assign(expr syntax.Expr) {
 
 			// TODO(mdempsky): Minimize locals index size by deferring
 			// this until the variables actually come into scope.
-			w.addLocal(obj, false)
+			w.addLocal(obj)
 			return
 		}
 	}
@@ -1558,7 +1557,7 @@ func (w *writer) switchStmt(stmt *syntax.SwitchStmt) {
 
 			obj := obj.(*types2.Var)
 			w.typ(obj.Type())
-			w.addLocal(obj, false)
+			w.addLocal(obj)
 		}
 
 		w.stmts(clause.Body)
@@ -2177,6 +2176,15 @@ func (w *writer) rtype(typ types2.Type) {
 	}
 }
 
+// varDictIndex writes out information for populating DictIndex for
+// the ir.Name that will represent obj.
+func (w *writer) varDictIndex(obj *types2.Var) {
+	info := w.p.typIdx(obj.Type(), w.dict)
+	if w.Bool(info.derived) {
+		w.Len(w.dict.rtypeIdx(info))
+	}
+}
+
 func isUntyped(typ types2.Type) bool {
 	basic, ok := typ.(*types2.Basic)
 	return ok && basic.Info()&types2.IsUntyped != 0

src/cmd/link/internal/ld/dwarf_test.go

@@ -11,7 +11,6 @@ import (
 	"debug/dwarf"
 	"debug/pe"
 	"fmt"
-	"internal/buildcfg"
 	"internal/testenv"
 	"io"
 	"io/ioutil"
@@ -1597,9 +1596,6 @@ func TestDictIndex(t *testing.T) {
 	if runtime.GOOS == "plan9" {
 		t.Skip("skipping on plan9; no DWARF symbol table in executables")
 	}
-	if buildcfg.Experiment.Unified {
-		t.Skip("GOEXPERIMENT=unified does not emit dictionaries yet")
-	}
 	t.Parallel()
 
 	const prog = `