cmd/compile/internal/types: overhaul and simplify API

This CL removes a lot of the redundant methods for accessing struct
fields and signature parameters. In particular, users never have to
write ".Slice()" or ".FieldSlice()" anymore; the exported APIs just do
what you want.

Further internal refactorings to follow.

Change-Id: I45212f6772fe16aad39d0e68b82d71b0796e5639
Reviewed-on: https://go-review.googlesource.com/c/go/+/521295
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>

36 files changed, 241 insertions, 329 deletions

diff --git a/src/cmd/compile/internal/abi/abiutils.go b/src/cmd/compile/internal/abi/abiutils.go
index 7d3da3c66d..f8e4e8ae0d 100644
--- a/src/cmd/compile/internal/abi/abiutils.go
+++ b/src/cmd/compile/internal/abi/abiutils.go
@@ -173,7 +173,7 @@ func appendParamTypes(rts []*types.Type, t *types.Type) []*types.Type {
 				rts = appendParamTypes(rts, t.Elem())
 			}
 		case types.TSTRUCT:
-			for _, f := range t.FieldSlice() {
+			for _, f := range t.Fields() {
 				if f.Type.Size() > 0 { // embedded zero-width types receive no registers
 					rts = appendParamTypes(rts, f.Type)
 				}
@@ -212,7 +212,7 @@ func appendParamOffsets(offsets []int64, at int64, t *types.Type) ([]int64, int6
 				offsets, at = appendParamOffsets(offsets, at, t.Elem())
 			}
 		case types.TSTRUCT:
-			for i, f := range t.FieldSlice() {
+			for i, f := range t.Fields() {
 				offsets, at = appendParamOffsets(offsets, at, f.Type)
 				if f.Type.Size() == 0 && i == t.NumFields()-1 {
 					at++ // last field has zero width
@@ -310,7 +310,7 @@ func (a *ABIConfig) NumParamRegs(t *types.Type) int {
 		case types.TARRAY:
 			n = a.NumParamRegs(t.Elem()) * int(t.NumElem())
 		case types.TSTRUCT:
-			for _, f := range t.FieldSlice() {
+			for _, f := range t.Fields() {
 				n += a.NumParamRegs(f.Type)
 			}
 		case types.TSLICE:
@@ -397,7 +397,7 @@ func (config *ABIConfig) ABIAnalyzeFuncType(ft *types.Type) *ABIParamResultInfo
 	}
 
 	// Inputs
-	ifsl := ft.Params().FieldSlice()
+	ifsl := ft.Params()
 	for _, f := range ifsl {
 		result.inparams = append(result.inparams,
 			s.assignParamOrReturn(f.Type, f.Nname, false))
@@ -407,7 +407,7 @@ func (config *ABIConfig) ABIAnalyzeFuncType(ft *types.Type) *ABIParamResultInfo
 
 	// Outputs
 	s.rUsed = RegAmounts{}
-	ofsl := ft.Results().FieldSlice()
+	ofsl := ft.Results()
 	for _, f := range ofsl {
 		result.outparams = append(result.outparams, s.assignParamOrReturn(f.Type, f.Nname, true))
 	}
@@ -435,10 +435,10 @@ func (config *ABIConfig) ABIAnalyze(t *types.Type, setNname bool) *ABIParamResul
 		config.updateOffset(result, t.Recv(), result.inparams[0], false, setNname)
 		k++
 	}
-	for i, f := range t.Params().FieldSlice() {
+	for i, f := range t.Params() {
 		config.updateOffset(result, f, result.inparams[k+i], false, setNname)
 	}
-	for i, f := range t.Results().FieldSlice() {
+	for i, f := range t.Results() {
 		config.updateOffset(result, f, result.outparams[i], true, setNname)
 	}
 	return result
@@ -583,7 +583,7 @@ func (state *assignState) allocateRegs(regs []RegIndex, t *types.Type) []RegInde
 			}
 			return regs
 		case types.TSTRUCT:
-			for _, f := range t.FieldSlice() {
+			for _, f := range t.Fields() {
 				regs = state.allocateRegs(regs, f.Type)
 			}
 			return regs
@@ -690,7 +690,7 @@ func (state *assignState) regassignArray(t *types.Type) bool {
 // some other enclosing type) to determine if it can be register
 // assigned. Returns TRUE if we can register allocate, FALSE otherwise.
 func (state *assignState) regassignStruct(t *types.Type) bool {
-	for _, field := range t.FieldSlice() {
+	for _, field := range t.Fields() {
 		if !state.regassign(field.Type) {
 			return false
 		}
diff --git a/src/cmd/compile/internal/compare/compare.go b/src/cmd/compile/internal/compare/compare.go
index 2f6db78b74..5dd5eec8de 100644
--- a/src/cmd/compile/internal/compare/compare.go
+++ b/src/cmd/compile/internal/compare/compare.go
@@ -70,7 +70,7 @@ func EqCanPanic(t *types.Type) bool {
 	case types.TARRAY:
 		return EqCanPanic(t.Elem())
 	case types.TSTRUCT:
-		for _, f := range t.FieldSlice() {
+		for _, f := range t.Fields() {
 			if !f.Sym.IsBlank() && EqCanPanic(f.Type) {
 				return true
 			}
@@ -87,7 +87,7 @@ func EqCanPanic(t *types.Type) bool {
 func EqStructCost(t *types.Type) int64 {
 	cost := int64(0)
 
-	for i, fields := 0, t.FieldSlice(); i < len(fields); {
+	for i, fields := 0, t.Fields(); i < len(fields); {
 		f := fields[i]
 
 		// Skip blank-named fields.
@@ -181,7 +181,7 @@ func EqStruct(t *types.Type, np, nq ir.Node) ([]ir.Node, bool) {
 
 	// Walk the struct using memequal for runs of AMEM
 	// and calling specific equality tests for the others.
-	for i, fields := 0, t.FieldSlice(); i < len(fields); {
+	for i, fields := 0, t.Fields(); i < len(fields); {
 		f := fields[i]
 
 		// Skip blank-named fields.
diff --git a/src/cmd/compile/internal/devirtualize/devirtualize.go b/src/cmd/compile/internal/devirtualize/devirtualize.go
index ae9f24d9a5..5e91104eeb 100644
--- a/src/cmd/compile/internal/devirtualize/devirtualize.go
+++ b/src/cmd/compile/internal/devirtualize/devirtualize.go
@@ -142,9 +142,9 @@ func staticCall(call *ir.CallExpr) {
 	switch ft := x.Type(); ft.NumResults() {
 	case 0:
 	case 1:
-		call.SetType(ft.Results().Field(0).Type)
+		call.SetType(ft.Result(0).Type)
 	default:
-		call.SetType(ft.Results())
+		call.SetType(ft.ResultsTuple())
 	}
 
 	// Desugar OCALLMETH, if we created one (#57309).
diff --git a/src/cmd/compile/internal/devirtualize/pgo.go b/src/cmd/compile/internal/devirtualize/pgo.go
index 2b6eb145ac..800b32f6eb 100644
--- a/src/cmd/compile/internal/devirtualize/pgo.go
+++ b/src/cmd/compile/internal/devirtualize/pgo.go
@@ -301,7 +301,7 @@ func rewriteCondCall(call *ir.CallExpr, curfn, callee *ir.Func, concretetyp *typ
 
 	sig := call.X.Type()
 
-	for _, ret := range sig.Results().FieldSlice() {
+	for _, ret := range sig.Results() {
 		retvars = append(retvars, typecheck.TempAt(base.Pos, curfn, ret.Type))
 	}
 
diff --git a/src/cmd/compile/internal/dwarfgen/dwarf.go b/src/cmd/compile/internal/dwarfgen/dwarf.go
index 886250a62f..b3c97cb0c6 100644
--- a/src/cmd/compile/internal/dwarfgen/dwarf.go
+++ b/src/cmd/compile/internal/dwarfgen/dwarf.go
@@ -270,9 +270,8 @@ func createDwarfVars(fnsym *obj.LSym, complexOK bool, fn *ir.Func, apDecls []*ir
 func sortDeclsAndVars(fn *ir.Func, decls []*ir.Name, vars []*dwarf.Var) {
 	paramOrder := make(map[*ir.Name]int)
 	idx := 1
-	for _, selfn := range types.RecvsParamsResults {
-		fsl := selfn(fn.Type()).FieldSlice()
-		for _, f := range fsl {
+	for _, selfn := range &types.RecvsParamsResults {
+		for _, f := range selfn(fn.Type()) {
 			if n, ok := f.Nname.(*ir.Name); ok {
 				paramOrder[n] = idx
 				idx++
diff --git a/src/cmd/compile/internal/escape/call.go b/src/cmd/compile/internal/escape/call.go
index 0caec2f6b9..360094ee44 100644
--- a/src/cmd/compile/internal/escape/call.go
+++ b/src/cmd/compile/internal/escape/call.go
@@ -49,7 +49,7 @@ func (e *escape) call(ks []hole, call ir.Node) {
 		}
 
 		if ks != nil && fn != nil && e.inMutualBatch(fn) {
-			for i, result := range fn.Type().Results().FieldSlice() {
+			for i, result := range fn.Type().Results() {
 				e.expr(ks[i], result.Nname.(*ir.Name))
 			}
 		}
@@ -93,7 +93,7 @@ func (e *escape) call(ks []hole, call ir.Node) {
 			argumentParam(recvParam, recvArg)
 		}
 
-		for i, param := range fntype.Params().FieldSlice() {
+		for i, param := range fntype.Params() {
 			argumentParam(param, args[i])
 		}
 
diff --git a/src/cmd/compile/internal/escape/escape.go b/src/cmd/compile/internal/escape/escape.go
index f38bcadb3e..b0c17ccb83 100644
--- a/src/cmd/compile/internal/escape/escape.go
+++ b/src/cmd/compile/internal/escape/escape.go
@@ -195,7 +195,7 @@ func (b *batch) initFunc(fn *ir.Func) {
 	}
 
 	// Initialize resultIndex for result parameters.
-	for i, f := range fn.Type().Results().FieldSlice() {
+	for i, f := range fn.Type().Results() {
 		e.oldLoc(f.Nname.(*ir.Name)).resultIndex = 1 + i
 	}
 }
@@ -275,7 +275,7 @@ func (b *batch) finish(fns []*ir.Func) {
 
 		narg := 0
 		for _, fs := range &types.RecvsParams {
-			for _, f := range fs(fn.Type()).Fields().Slice() {
+			for _, f := range fs(fn.Type()) {
 				narg++
 				f.Note = b.paramTag(fn, narg, f)
 			}
@@ -485,7 +485,7 @@ func (b *batch) reportLeaks(pos src.XPos, name string, esc leaks, sig *types.Typ
 	}
 	for i := 0; i < numEscResults; i++ {
 		if x := esc.Result(i); x >= 0 {
-			res := sig.Results().Field(i).Sym
+			res := sig.Result(i).Sym
 			base.WarnfAt(pos, "leaking param: %v to result %v level=%d", name, res, x)
 			warned = true
 		}
diff --git a/src/cmd/compile/internal/escape/solve.go b/src/cmd/compile/internal/escape/solve.go
index fc634e04a7..2675a16a24 100644
--- a/src/cmd/compile/internal/escape/solve.go
+++ b/src/cmd/compile/internal/escape/solve.go
@@ -70,7 +70,7 @@ func (b *batch) walkOne(root *location, walkgen uint32, enqueue func(*location))
 
 				// Re-flow from the closure's results, now that we're aware
 				// we lost track of them.
-				for _, result := range fn.Type().Results().FieldSlice() {
+				for _, result := range fn.Type().Results() {
 					enqueue(b.oldLoc(result.Nname.(*ir.Name)))
 				}
 			}
diff --git a/src/cmd/compile/internal/escape/stmt.go b/src/cmd/compile/internal/escape/stmt.go
index 8b66c14cb6..bbd5113d5d 100644
--- a/src/cmd/compile/internal/escape/stmt.go
+++ b/src/cmd/compile/internal/escape/stmt.go
@@ -177,7 +177,7 @@ func (e *escape) stmt(n ir.Node) {
 		e.reassigned(ks, n)
 	case ir.ORETURN:
 		n := n.(*ir.ReturnStmt)
-		results := e.curfn.Type().Results().FieldSlice()
+		results := e.curfn.Type().Results()
 		dsts := make([]ir.Node, len(results))
 		for i, res := range results {
 			dsts[i] = res.Nname.(*ir.Name)
diff --git a/src/cmd/compile/internal/gc/export.go b/src/cmd/compile/internal/gc/export.go
index 6d73c38d0b..c93f008ba2 100644
--- a/src/cmd/compile/internal/gc/export.go
+++ b/src/cmd/compile/internal/gc/export.go
@@ -39,7 +39,7 @@ func dumpasmhdr() {
 				break
 			}
 			fmt.Fprintf(b, "#define %s__size %d\n", n.Sym().Name, int(t.Size()))
-			for _, f := range t.Fields().Slice() {
+			for _, f := range t.Fields() {
 				if !f.Sym.IsBlank() {
 					fmt.Fprintf(b, "#define %s_%s %d\n", n.Sym().Name, f.Sym.Name, int(f.Offset))
 				}
diff --git a/src/cmd/compile/internal/inline/inl.go b/src/cmd/compile/internal/inline/inl.go
index cc567b6fce..bb3d872d75 100644
--- a/src/cmd/compile/internal/inline/inl.go
+++ b/src/cmd/compile/internal/inline/inl.go
@@ -464,7 +464,7 @@ func canDelayResults(fn *ir.Func) bool {
 	}
 
 	// temporaries for return values.
-	for _, param := range fn.Type().Results().FieldSlice() {
+	for _, param := range fn.Type().Results() {
 		if sym := types.OrigSym(param.Sym); sym != nil && !sym.IsBlank() {
 			return false // found a named result parameter (case 3)
 		}
diff --git a/src/cmd/compile/internal/ir/expr.go b/src/cmd/compile/internal/ir/expr.go
index 63a6a3eed2..5678ce436d 100644
--- a/src/cmd/compile/internal/ir/expr.go
+++ b/src/cmd/compile/internal/ir/expr.go
@@ -1116,7 +1116,7 @@ func IsReflectHeaderDataField(l Node) bool {
 
 func ParamNames(ft *types.Type) []Node {
 	args := make([]Node, ft.NumParams())
-	for i, f := range ft.Params().FieldSlice() {
+	for i, f := range ft.Params() {
 		args[i] = f.Nname.(*Name)
 	}
 	return args
diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index b1829faf7f..d8508e0492 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -490,7 +490,7 @@ func IsMethod(n Node) bool {
 
 func HasNamedResults(fn *Func) bool {
 	typ := fn.Type()
-	return typ.NumResults() > 0 && types.OrigSym(typ.Results().Field(0).Sym) != nil
+	return typ.NumResults() > 0 && types.OrigSym(typ.Result(0).Sym) != nil
 }
 
 // HasUniquePos reports whether n has a unique position that can be
diff --git a/src/cmd/compile/internal/liveness/plive.go b/src/cmd/compile/internal/liveness/plive.go
index 6916a5eb17..85e988aeda 100644
--- a/src/cmd/compile/internal/liveness/plive.go
+++ b/src/cmd/compile/internal/liveness/plive.go
@@ -1071,7 +1071,7 @@ func clobberWalk(b *ssa.Block, v *ir.Name, offset int64, t *types.Type) {
 		}
 
 	case types.TSTRUCT:
-		for _, t1 := range t.Fields().Slice() {
+		for _, t1 := range t.Fields() {
 			clobberWalk(b, v, offset+t1.Offset, t1.Type)
 		}
 
diff --git a/src/cmd/compile/internal/noder/linker.go b/src/cmd/compile/internal/noder/linker.go
index 0efe6b630b..71e57741a0 100644
--- a/src/cmd/compile/internal/noder/linker.go
+++ b/src/cmd/compile/internal/noder/linker.go
@@ -201,7 +201,7 @@ func (l *linker) relocObj(pr *pkgReader, idx pkgbits.Index) pkgbits.Index {
 
 		if obj.Op() == ir.OTYPE && !obj.Alias() {
 			if typ := obj.Type(); !typ.IsInterface() {
-				for _, method := range typ.Methods().Slice() {
+				for _, method := range typ.Methods() {
 					l.exportBody(method.Nname.(*ir.Name), local)
 				}
 			}
@@ -290,7 +290,7 @@ func (l *linker) relocFuncExt(w *pkgbits.Encoder, name *ir.Name) {
 
 	// Escape analysis.
 	for _, fs := range &types.RecvsParams {
-		for _, f := range fs(name.Type()).FieldSlice() {
+		for _, f := range fs(name.Type()) {
 			w.String(f.Note)
 		}
 	}
@@ -315,7 +315,7 @@ func (l *linker) relocTypeExt(w *pkgbits.Encoder, name *ir.Name) {
 	l.lsymIdx(w, "", reflectdata.TypeLinksym(typ.PtrTo()))
 
 	if typ.Kind() != types.TINTER {
-		for _, method := range typ.Methods().Slice() {
+		for _, method := range typ.Methods() {
 			l.relocFuncExt(w, method.Nname.(*ir.Name))
 		}
 	}
diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index 008d7d5598..6ab7b272a6 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -809,7 +809,7 @@ func (pr *pkgReader) objIdx(idx pkgbits.Index, implicits, explicits []*types.Typ
 			methods[i] = r.method(rext)
 		}
 		if len(methods) != 0 {
-			typ.Methods().Set(methods)
+			typ.SetMethods(methods)
 		}
 
 		if !r.dict.shaped {
@@ -1110,7 +1110,7 @@ func (r *reader) funcExt(name *ir.Name, method *types.Sym) {
 
 		// Escape analysis.
 		for _, fs := range &types.RecvsParams {
-			for _, f := range fs(name.Type()).FieldSlice() {
+			for _, f := range fs(name.Type()) {
 				f.Note = r.String()
 			}
 		}
@@ -1355,8 +1355,8 @@ func (r *reader) syntheticArgs(pos src.XPos) (recvs, params ir.Nodes) {
 		}
 	}
 
-	addParams(&recvs, sig.Recvs().FieldSlice())
-	addParams(&params, sig.Params().FieldSlice())
+	addParams(&recvs, sig.Recvs())
+	addParams(&params, sig.Params())
 	return
 }
 
@@ -1500,11 +1500,11 @@ func (r *reader) funcargs(fn *ir.Func) {
 	if recv := sig.Recv(); recv != nil {
 		r.funcarg(recv, recv.Sym, ir.PPARAM)
 	}
-	for _, param := range sig.Params().FieldSlice() {
+	for _, param := range sig.Params() {
 		r.funcarg(param, param.Sym, ir.PPARAM)
 	}
 
-	for i, param := range sig.Results().FieldSlice() {
+	for i, param := range sig.Results() {
 		sym := types.OrigSym(param.Sym)
 
 		if sym == nil || sym.IsBlank() {
@@ -2201,7 +2201,7 @@ func (r *reader) expr() (res ir.Node) {
 			// interface method values).
 			//
 			if recv.Type().HasShape() {
-				typ := wrapperFn.Type().Params().Field(0).Type
+				typ := wrapperFn.Type().Param(0).Type
 				if !types.Identical(typ, recv.Type()) {
 					base.FatalfAt(wrapperFn.Pos(), "receiver %L does not match %L", recv, wrapperFn)
 				}
@@ -2263,7 +2263,7 @@ func (r *reader) expr() (res ir.Node) {
 		// rather than types.Identical, because the latter can be confused
 		// by tricky promoted methods (e.g., typeparam/mdempsky/21.go).
 		if wrapperFn != nil && len(implicits) == 0 && !deref && !addr {
-			if !types.Identical(recv, wrapperFn.Type().Params().Field(0).Type) {
+			if !types.Identical(recv, wrapperFn.Type().Param(0).Type) {
 				base.FatalfAt(pos, "want receiver type %v, but have method %L", recv, wrapperFn)
 			}
 			return wrapperFn
@@ -2563,7 +2563,7 @@ func (r *reader) funcInst(pos src.XPos) (wrapperFn, baseFn, dictPtr ir.Node) {
 
 		// TODO(mdempsky): Is there a more robust way to get the
 		// dictionary pointer type here?
-		dictPtrType := baseFn.Type().Params().Field(0).Type
+		dictPtrType := baseFn.Type().Param(0).Type
 		dictPtr = typecheck.Expr(ir.NewConvExpr(pos, ir.OCONVNOP, dictPtrType, r.dictWord(pos, r.dict.subdictsOffset()+idx)))
 
 		return
@@ -2788,7 +2788,7 @@ func syntheticSig(sig *types.Type) (params, results []*types.Field) {
 		return res
 	}
 
-	return clone(sig.Params().FieldSlice()), clone(sig.Results().FieldSlice())
+	return clone(sig.Params()), clone(sig.Results())
 }
 
 func (r *reader) optExpr() ir.Node {
@@ -2866,7 +2866,7 @@ func (r *reader) methodExpr() (wrapperFn, baseFn, dictPtr ir.Node) {
 
 		// TODO(mdempsky): Is there a more robust way to get the
 		// dictionary pointer type here?
-		dictPtrType := shapedFn.Type().Params().Field(1).Type
+		dictPtrType := shapedFn.Type().Param(1).Type
 		dictPtr := typecheck.Expr(ir.NewConvExpr(pos, ir.OCONVNOP, dictPtrType, r.dictWord(pos, r.dict.subdictsOffset()+idx)))
 
 		return nil, shapedFn, dictPtr
@@ -2883,7 +2883,7 @@ func (r *reader) methodExpr() (wrapperFn, baseFn, dictPtr ir.Node) {
 		dictPtr := typecheck.Expr(ir.NewAddrExpr(pos, dict))
 
 		// Check that dictPtr matches shapedFn's dictionary parameter.
-		if !types.Identical(dictPtr.Type(), shapedFn.Type().Params().Field(1).Type) {
+		if !types.Identical(dictPtr.Type(), shapedFn.Type().Param(1).Type) {
 			base.FatalfAt(pos, "dict %L, but shaped method %L", dict, shapedFn)
 		}
 
@@ -2911,7 +2911,7 @@ func shapedMethodExpr(pos src.XPos, obj *ir.Name, sym *types.Sym) *ir.SelectorEx
 	assert(typ.HasShape())
 
 	method := func() *types.Field {
-		for _, method := range typ.Methods().Slice() {
+		for _, method := range typ.Methods() {
 			if method.Sym == sym {
 				return method
 			}
@@ -3770,7 +3770,7 @@ func wrapType(typ *types.Type, target *ir.Package, seen map[string]*types.Type,
 	if !typ.IsInterface() {
 		typecheck.CalcMethods(typ)
 	}
-	for _, meth := range typ.AllMethods().Slice() {
+	for _, meth := range typ.AllMethods() {
 		if meth.Sym.IsBlank() || !meth.IsMethod() {
 			base.FatalfAt(meth.Pos, "invalid method: %v", meth)
 		}
@@ -3865,8 +3865,8 @@ func newWrapperFunc(pos src.XPos, sym *types.Sym, wrapper *types.Type, method *t
 	fn.SetDupok(true) // TODO(mdempsky): Leave unset for local, non-generic wrappers?
 
 	// TODO(mdempsky): De-duplicate with similar logic in funcargs.
-	defParams := func(class ir.Class, params *types.Type) {
-		for _, param := range params.FieldSlice() {
+	defParams := func(class ir.Class, params []*types.Field) {
+		for _, param := range params {
 			param.Nname = fn.NewLocal(param.Pos, param.Sym, class, param.Type)
 		}
 	}
@@ -3929,8 +3929,8 @@ func newWrapperType(recvType *types.Type, method *types.Field) *types.Type {
 	if recvType != nil {
 		recv = types.NewField(sig.Recv().Pos, typecheck.Lookup(".this"), recvType)
 	}
-	params := clone(sig.Params().FieldSlice())
-	results := clone(sig.Results().FieldSlice())
+	params := clone(sig.Params())
+	results := clone(sig.Results())
 
 	return types.NewSignature(recv, params, results)
 }
@@ -3938,7 +3938,7 @@ func newWrapperType(recvType *types.Type, method *types.Field) *types.Type {
 func addTailCall(pos src.XPos, fn *ir.Func, recv ir.Node, method *types.Field) {
 	sig := fn.Nname.Type()
 	args := make([]ir.Node, sig.NumParams())
-	for i, param := range sig.Params().FieldSlice() {
+	for i, param := range sig.Params() {
 		args[i] = param.Nname.(*ir.Name)
 	}
 
@@ -3987,16 +3987,16 @@ func shapeSig(fn *ir.Func, dict *readerDict) *types.Type {
 		recv = types.NewField(oldRecv.Pos, oldRecv.Sym, oldRecv.Type)
 	}
 
-	params := make([]*types.Field, 1+sig.Params().Fields().Len())
+	params := make([]*types.Field, 1+sig.NumParams())
 	params[0] = types.NewField(fn.Pos(), fn.Sym().Pkg.Lookup(dictParamName), types.NewPtr(dict.varType()))
-	for i, param := range sig.Params().Fields().Slice() {
+	for i, param := range sig.Params() {
 		d := types.NewField(param.Pos, param.Sym, param.Type)
 		d.SetIsDDD(param.IsDDD())
 		params[1+i] = d
 	}
 
-	results := make([]*types.Field, sig.Results().Fields().Len())
-	for i, result := range sig.Results().Fields().Slice() {
+	results := make([]*types.Field, sig.NumResults())
+	for i, result := range sig.Results() {
 		results[i] = types.NewField(result.Pos, result.Sym, result.Type)
 	}
 
diff --git a/src/cmd/compile/internal/reflectdata/alg.go b/src/cmd/compile/internal/reflectdata/alg.go
index 29f9c79393..32af785feb 100644
--- a/src/cmd/compile/internal/reflectdata/alg.go
+++ b/src/cmd/compile/internal/reflectdata/alg.go
@@ -115,7 +115,7 @@ func genhash(t *types.Type) *obj.LSym {
 	case types.TARRAY:
 		genhash(t.Elem())
 	case types.TSTRUCT:
-		for _, f := range t.FieldSlice() {
+		for _, f := range t.Fields() {
 			genhash(f.Type)
 		}
 	}
@@ -190,7 +190,7 @@ func hashFunc(t *types.Type) *ir.Func {
 	case types.TSTRUCT:
 		// Walk the struct using memhash for runs of AMEM
 		// and calling specific hash functions for the others.
-		for i, fields := 0, t.FieldSlice(); i < len(fields); {
+		for i, fields := 0, t.Fields(); i < len(fields); {
 			f := fields[i]
 
 			// Skip blank fields.
diff --git a/src/cmd/compile/internal/reflectdata/reflect.go b/src/cmd/compile/internal/reflectdata/reflect.go
index d593a312bd..93506a8fdf 100644
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@@ -329,7 +329,7 @@ func methods(t *types.Type) []*typeSig {
 	// make list of methods for t,
 	// generating code if necessary.
 	var ms []*typeSig
-	for _, f := range mt.AllMethods().Slice() {
+	for _, f := range mt.AllMethods() {
 		if f.Sym == nil {
 			base.Fatalf("method with no sym on %v", mt)
 		}
@@ -376,7 +376,7 @@ func methods(t *types.Type) []*typeSig {
 // imethods returns the methods of the interface type t, sorted by name.
 func imethods(t *types.Type) []*typeSig {
 	var methods []*typeSig
-	for _, f := range t.AllMethods().Slice() {
+	for _, f := range t.AllMethods() {
 		if f.Type.Kind() != types.TFUNC || f.Sym == nil {
 			continue
 		}
@@ -901,7 +901,7 @@ func needkeyupdate(t *types.Type) bool {
 		return needkeyupdate(t.Elem())
 
 	case types.TSTRUCT:
-		for _, t1 := range t.Fields().Slice() {
+		for _, t1 := range t.Fields() {
 			if needkeyupdate(t1.Type) {
 				return true
 			}
@@ -924,7 +924,7 @@ func hashMightPanic(t *types.Type) bool {
 		return hashMightPanic(t.Elem())
 
 	case types.TSTRUCT:
-		for _, t1 := range t.Fields().Slice() {
+		for _, t1 := range t.Fields() {
 			if hashMightPanic(t1.Type) {
 				return true
 			}
@@ -1027,15 +1027,15 @@ func writeType(t *types.Type) *obj.LSym {
 		ot = dextratype(lsym, ot, t, 0)
 
 	case types.TFUNC:
-		for _, t1 := range t.Recvs().Fields().Slice() {
+		for _, t1 := range t.Recvs() {
 			writeType(t1.Type)
 		}
 		isddd := false
-		for _, t1 := range t.Params().Fields().Slice() {
+		for _, t1 := range t.Params() {
 			isddd = t1.IsDDD()
 			writeType(t1.Type)
 		}
-		for _, t1 := range t.Results().Fields().Slice() {
+		for _, t1 := range t.Results() {
 			writeType(t1.Type)
 		}
 
@@ -1055,13 +1055,13 @@ func writeType(t *types.Type) *obj.LSym {
 		ot = dextratype(lsym, ot, t, dataAdd)
 
 		// Array of rtype pointers follows funcType.
-		for _, t1 := range t.Recvs().Fields().Slice() {
+		for _, t1 := range t.Recvs() {
 			ot = objw.SymPtr(lsym, ot, writeType(t1.Type), 0)
 		}
-		for _, t1 := range t.Params().Fields().Slice() {
+		for _, t1 := range t.Params() {
 			ot = objw.SymPtr(lsym, ot, writeType(t1.Type), 0)
 		}
-		for _, t1 := range t.Results().Fields().Slice() {
+		for _, t1 := range t.Results() {
 			ot = objw.SymPtr(lsym, ot, writeType(t1.Type), 0)
 		}
 
@@ -1169,7 +1169,7 @@ func writeType(t *types.Type) *obj.LSym {
 	// ../../../../runtime/type.go:/structType
 	// for security, only the exported fields.
 	case types.TSTRUCT:
-		fields := t.Fields().Slice()
+		fields := t.Fields()
 		for _, t1 := range fields {
 			writeType(t1.Type)
 		}
@@ -1305,7 +1305,7 @@ func writeITab(lsym *obj.LSym, typ, iface *types.Type, allowNonImplement bool) {
 		base.Fatalf("writeITab(%v, %v)", typ, iface)
 	}
 
-	sigs := iface.AllMethods().Slice()
+	sigs := iface.AllMethods()
 	entries := make([]*obj.LSym, 0, len(sigs))
 
 	// both sigs and methods are sorted by name,
@@ -1403,8 +1403,8 @@ func writtenByWriteBasicTypes(typ *types.Type) bool {
 		// func(error) string
 		if typ.NumRecvs() == 0 &&
 			typ.NumParams() == 1 && typ.NumResults() == 1 &&
-			typ.Params().FieldType(0) == types.ErrorType &&
-			typ.Results().FieldType(0) == types.Types[types.TSTRING] {
+			typ.Param(0).Type == types.ErrorType &&
+			typ.Result(0).Type == types.Types[types.TSTRING] {
 			return true
 		}
 	}
@@ -1510,8 +1510,8 @@ func (a typesByString) Less(i, j int) bool {
 	// will be equal for the above checks, but different in DWARF output.
 	// Sort by source position to ensure deterministic order.
 	// See issues 27013 and 30202.
-	if a[i].t.Kind() == types.TINTER && a[i].t.AllMethods().Len() > 0 {
-		return a[i].t.AllMethods().Index(0).Pos.Before(a[j].t.AllMethods().Index(0).Pos)
+	if a[i].t.Kind() == types.TINTER && len(a[i].t.AllMethods()) > 0 {
+		return a[i].t.AllMethods()[0].Pos.Before(a[j].t.AllMethods()[0].Pos)
 	}
 	return false
 }
@@ -1735,7 +1735,7 @@ func (p *gcProg) emit(t *types.Type, offset int64) {
 		p.w.Repeat(elem.Size()/int64(types.PtrSize), count-1)
 
 	case types.TSTRUCT:
-		for _, t1 := range t.Fields().Slice() {
+		for _, t1 := range t.Fields() {
 			p.emit(t1.Type, offset+t1.Offset)
 		}
 	}
diff --git a/src/cmd/compile/internal/ssagen/abi.go b/src/cmd/compile/internal/ssagen/abi.go
index bec30c9f2c..a5f1a2db60 100644
--- a/src/cmd/compile/internal/ssagen/abi.go
+++ b/src/cmd/compile/internal/ssagen/abi.go
@@ -253,8 +253,8 @@ func makeABIWrapper(f *ir.Func, wrapperABI obj.ABI) {
 	// Reuse f's types.Sym to create a new ODCLFUNC/function.
 	// TODO(mdempsky): Means we can't set sym.Def in Declfunc, ugh.
 	fn := ir.NewFunc(pos, pos, f.Sym(), types.NewSignature(nil,
-		typecheck.NewFuncParams(ft.Params().FieldSlice(), true),
-		typecheck.NewFuncParams(ft.Results().FieldSlice(), false)))
+		typecheck.NewFuncParams(ft.Params(), true),
+		typecheck.NewFuncParams(ft.Results(), false)))
 	fn.ABI = wrapperABI
 	typecheck.DeclFunc(fn)
 
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 1ce00281b7..89e14786b0 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -411,7 +411,7 @@ func buildssa(fn *ir.Func, worker int) *ssa.Func {
 	if s.hasOpenDefers {
 		// Similarly, skip if there are any heap-allocated result
 		// parameters that need to be copied back to their stack slots.
-		for _, f := range s.curfn.Type().Results().FieldSlice() {
+		for _, f := range s.curfn.Type().Results() {
 			if !f.Nname.(*ir.Name).OnStack() {
 				s.hasOpenDefers = false
 				break
@@ -619,7 +619,7 @@ func (s *state) storeParameterRegsToStack(abi *abi.ABIConfig, paramAssignment *a
 // are always live, so we need to zero them before any allocations,
 // even allocations to move params/results to the heap.
 func (s *state) zeroResults() {
-	for _, f := range s.curfn.Type().Results().FieldSlice() {
+	for _, f := range s.curfn.Type().Results() {
 		n := f.Nname.(*ir.Name)
 		if !n.OnStack() {
 			// The local which points to the return value is the
@@ -642,8 +642,8 @@ func (s *state) zeroResults() {
 // paramsToHeap produces code to allocate memory for heap-escaped parameters
 // and to copy non-result parameters' values from the stack.
 func (s *state) paramsToHeap() {
-	do := func(params *types.Type) {
-		for _, f := range params.FieldSlice() {
+	do := func(params []*types.Field) {
+		for _, f := range params {
 			if f.Nname == nil {
 				continue // anonymous or blank parameter
 			}
@@ -1248,7 +1248,7 @@ func (s *state) instrumentFields(t *types.Type, addr *ssa.Value, kind instrument
 		s.instrument(t, addr, kind)
 		return
 	}
-	for _, f := range t.Fields().Slice() {
+	for _, f := range t.Fields() {
 		if f.Sym.IsBlank() {
 			continue
 		}
@@ -2032,7 +2032,7 @@ func (s *state) exit() *ssa.Block {
 	var m *ssa.Value
 	// Do actual return.
 	// These currently turn into self-copies (in many cases).
-	resultFields := s.curfn.Type().Results().FieldSlice()
+	resultFields := s.curfn.Type().Results()
 	results := make([]*ssa.Value, len(resultFields)+1, len(resultFields)+1)
 	m = s.newValue0(ssa.OpMakeResult, s.f.OwnAux.LateExpansionResultType())
 	// Store SSAable and heap-escaped PPARAMOUT variables back to stack locations.
@@ -5318,7 +5318,7 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		}
 
 		for i, n := range args {
-			callArgs = append(callArgs, s.putArg(n, t.Params().Field(i).Type))
+			callArgs = append(callArgs, s.putArg(n, t.Param(i).Type))
 		}
 
 		callArgs = append(callArgs, s.mem())
@@ -5388,11 +5388,11 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		s.startBlock(bNext)
 	}
 
-	if res.NumFields() == 0 || k != callNormal {
+	if len(res) == 0 || k != callNormal {
 		// call has no return value. Continue with the next statement.
 		return nil
 	}
-	fp := res.Field(0)
+	fp := res[0]
 	if returnResultAddr {
 		return s.resultAddrOfCall(call, 0, fp.Type)
 	}
@@ -5621,7 +5621,7 @@ func TypeOK(t *types.Type) bool {
 		if t.NumFields() > ssa.MaxStruct {
 			return false
 		}
-		for _, t1 := range t.Fields().Slice() {
+		for _, t1 := range t.Fields() {
 			if !TypeOK(t1.Type) {
 				return false
 			}
@@ -6964,7 +6964,7 @@ func EmitArgInfo(f *ir.Func, abiInfo *abi.ABIParamResultInfo) *obj.LSym {
 				n++ // {} counts as a component
 				break
 			}
-			for _, field := range t.Fields().Slice() {
+			for _, field := range t.Fields() {
 				if !visitType(baseOffset+field.Offset, field.Type, depth) {
 					break
 				}
@@ -7924,7 +7924,7 @@ func fieldIdx(n *ir.SelectorExpr) int {
 		panic("ODOT's LHS is not a struct")
 	}
 
-	for i, f := range t.Fields().Slice() {
+	for i, f := range t.Fields() {
 		if f.Sym == n.Sel {
 			if f.Offset != n.Offset() {
 				panic("field offset doesn't match")
diff --git a/src/cmd/compile/internal/typebits/typebits.go b/src/cmd/compile/internal/typebits/typebits.go
index b533212e9e..b07f4374c2 100644
--- a/src/cmd/compile/internal/typebits/typebits.go
+++ b/src/cmd/compile/internal/typebits/typebits.go
@@ -86,7 +86,7 @@ func set(t *types.Type, off int64, bv bitvec.BitVec, skip bool) {
 		}
 
 	case types.TSTRUCT:
-		for _, f := range t.Fields().Slice() {
+		for _, f := range t.Fields() {
 			set(f.Type, off+f.Offset, bv, skip)
 		}
 
diff --git a/src/cmd/compile/internal/typecheck/dcl.go b/src/cmd/compile/internal/typecheck/dcl.go
index a78aad5abc..c25ea3448d 100644
--- a/src/cmd/compile/internal/typecheck/dcl.go
+++ b/src/cmd/compile/internal/typecheck/dcl.go
@@ -32,8 +32,8 @@ func DeclFunc(fn *ir.Func) (params, results []*ir.Name) {
 		base.FatalfAt(fn.Pos(), "unexpected receiver parameter")
 	}
 
-	params = declareParams(fn, ir.PPARAM, typ.Params().FieldSlice())
-	results = declareParams(fn, ir.PPARAMOUT, typ.Results().FieldSlice())
+	params = declareParams(fn, ir.PPARAM, typ.Params())
+	results = declareParams(fn, ir.PPARAMOUT, typ.Results())
 
 	funcStack = append(funcStack, ir.CurFunc)
 	ir.CurFunc = fn
@@ -156,18 +156,18 @@ func NewMethodType(sig *types.Type, recv *types.Type) *types.Type {
 	// TODO(mdempsky): Move this function to types.
 	// TODO(mdempsky): Preserve positions, names, and package from sig+recv.
 
-	params := make([]*types.Field, nrecvs+sig.Params().Fields().Len())
+	params := make([]*types.Field, nrecvs+sig.NumParams())
 	if recv != nil {
 		params[0] = types.NewField(base.Pos, nil, recv)
 	}
-	for i, param := range sig.Params().Fields().Slice() {
+	for i, param := range sig.Params() {
 		d := types.NewField(base.Pos, nil, param.Type)
 		d.SetIsDDD(param.IsDDD())
 		params[nrecvs+i] = d
 	}
 
-	results := make([]*types.Field, sig.Results().Fields().Len())
-	for i, t := range sig.Results().Fields().Slice() {
+	results := make([]*types.Field, sig.NumResults())
+	for i, t := range sig.Results() {
 		results[i] = types.NewField(base.Pos, nil, t.Type)
 	}
 
diff --git a/src/cmd/compile/internal/typecheck/func.go b/src/cmd/compile/internal/typecheck/func.go
index 5400fbee0b..414dd17826 100644
--- a/src/cmd/compile/internal/typecheck/func.go
+++ b/src/cmd/compile/internal/typecheck/func.go
@@ -41,7 +41,7 @@ func FixVariadicCall(call *ir.CallExpr) {
 	}
 
 	vi := fntype.NumParams() - 1
-	vt := fntype.Params().Field(vi).Type
+	vt := fntype.Param(vi).Type
 
 	args := call.Args
 	extra := args[vi:]
@@ -275,7 +275,7 @@ func tcCall(n *ir.CallExpr, top int) ir.Node {
 		return n
 	}
 	if t.NumResults() == 1 {
-		n.SetType(l.Type().Results().Field(0).Type)
+		n.SetType(l.Type().Result(0).Type)
 
 		if n.Op() == ir.OCALLFUNC && n.X.Op() == ir.ONAME {
 			if sym := n.X.(*ir.Name).Sym(); types.IsRuntimePkg(sym.Pkg) && sym.Name == "getg" {
@@ -297,7 +297,7 @@ func tcCall(n *ir.CallExpr, top int) ir.Node {
 		return n
 	}
 
-	n.SetType(l.Type().Results())
+	n.SetType(l.Type().ResultsTuple())
 	return n
 }
 
diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
index 0583635013..d72807a778 100644
--- a/src/cmd/compile/internal/typecheck/subr.go
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -158,13 +158,13 @@ func AddImplicitDots(n *ir.SelectorExpr) *ir.SelectorExpr {
 // CalcMethods calculates all the methods (including embedding) of a non-interface
 // type t.
 func CalcMethods(t *types.Type) {
-	if t == nil || t.AllMethods().Len() != 0 {
+	if t == nil || len(t.AllMethods()) != 0 {
 		return
 	}
 
 	// mark top-level method symbols
 	// so that expand1 doesn't consider them.
-	for _, f := range t.Methods().Slice() {
+	for _, f := range t.Methods() {
 		f.Sym.SetUniq(true)
 	}
 
@@ -201,11 +201,11 @@ func CalcMethods(t *types.Type) {
 		ms = append(ms, f)
 	}
 
-	for _, f := range t.Methods().Slice() {
+	for _, f := range t.Methods() {
 		f.Sym.SetUniq(false)
 	}
 
-	ms = append(ms, t.Methods().Slice()...)
+	ms = append(ms, t.Methods()...)
 	sort.Sort(types.MethodsByName(ms))
 	t.SetAllMethods(ms)
 }
@@ -243,13 +243,13 @@ func adddot1(s *types.Sym, t *types.Type, d int, save **types.Field, ignorecase
 		return c, false
 	}
 
-	var fields *types.Fields
+	var fields []*types.Field
 	if u.IsStruct() {
 		fields = u.Fields()
 	} else {
 		fields = u.AllMethods()
 	}
-	for _, f := range fields.Slice() {
+	for _, f := range fields {
 		if f.Embedded == 0 || f.Sym == nil {
 			continue
 		}
@@ -592,7 +592,7 @@ func expand0(t *types.Type) {
 	}
 
 	if u.IsInterface() {
-		for _, f := range u.AllMethods().Slice() {
+		for _, f := range u.AllMethods() {
 			if f.Sym.Uniq() {
 				continue
 			}
@@ -605,7 +605,7 @@ func expand0(t *types.Type) {
 
 	u = types.ReceiverBaseType(t)
 	if u != nil {
-		for _, f := range u.Methods().Slice() {
+		for _, f := range u.Methods() {
 			if f.Sym.Uniq() {
 				continue
 			}
@@ -631,13 +631,13 @@ func expand1(t *types.Type, top bool) {
 	}
 
 	if u.IsStruct() || u.IsInterface() {
-		var fields *types.Fields
+		var fields []*types.Field
 		if u.IsStruct() {
 			fields = u.Fields()
 		} else {
 			fields = u.AllMethods()
 		}
-		for _, f := range fields.Slice() {
+		for _, f := range fields {
 			if f.Embedded == 0 {
 				continue
 			}
@@ -716,8 +716,8 @@ func implements(t, iface *types.Type, m, samename **types.Field, ptr *int) bool
 
 	if t.IsInterface() {
 		i := 0
-		tms := t.AllMethods().Slice()
-		for _, im := range iface.AllMethods().Slice() {
+		tms := t.AllMethods()
+		for _, im := range iface.AllMethods() {
 			for i < len(tms) && tms[i].Sym != im.Sym {
 				i++
 			}
@@ -743,10 +743,10 @@ func implements(t, iface *types.Type, m, samename **types.Field, ptr *int) bool
 	var tms []*types.Field
 	if t != nil {
 		CalcMethods(t)
-		tms = t.AllMethods().Slice()
+		tms = t.AllMethods()
 	}
 	i := 0
-	for _, im := range iface.AllMethods().Slice() {
+	for _, im := range iface.AllMethods() {
 		for i < len(tms) && tms[i].Sym != im.Sym {
 			i++
 		}
@@ -811,13 +811,13 @@ func lookdot0(s *types.Sym, t *types.Type, save **types.Field, ignorecase bool)
 
 	c := 0
 	if u.IsStruct() || u.IsInterface() {
-		var fields *types.Fields
+		var fields []*types.Field
 		if u.IsStruct() {
 			fields = u.Fields()
 		} else {
 			fields = u.AllMethods()
 		}
-		for _, f := range fields.Slice() {
+		for _, f := range fields {
 			if f.Sym == s || (ignorecase && f.IsMethod() && strings.EqualFold(f.Sym.Name, s.Name)) {
 				if save != nil {
 					*save = f
@@ -834,7 +834,7 @@ func lookdot0(s *types.Sym, t *types.Type, save **types.Field, ignorecase bool)
 	}
 	u = types.ReceiverBaseType(u)
 	if u != nil {
-		for _, f := range u.Methods().Slice() {
+		for _, f := range u.Methods() {
 			if f.Embedded == 0 && (f.Sym == s || (ignorecase && strings.EqualFold(f.Sym.Name, s.Name))) {
 				if save != nil {
 					*save = f
diff --git a/src/cmd/compile/internal/typecheck/typecheck.go b/src/cmd/compile/internal/typecheck/typecheck.go
index a272f2a86b..a06fa7f5cd 100644
--- a/src/cmd/compile/internal/typecheck/typecheck.go
+++ b/src/cmd/compile/internal/typecheck/typecheck.go
@@ -688,7 +688,7 @@ func RewriteMultiValueCall(n ir.InitNode, call ir.Node) {
 	}
 
 	as := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, []ir.Node{call})
-	results := call.Type().FieldSlice()
+	results := call.Type().Fields()
 	list := make([]ir.Node, len(results))
 	for i, result := range results {
 		tmp := TempAt(base.Pos, ir.CurFunc, result.Type)
@@ -814,9 +814,9 @@ func needTwoArgs(n *ir.CallExpr) (ir.Node, ir.Node, bool) {
 // the matching field or nil. If dostrcmp is 0, it matches the symbols. If
 // dostrcmp is 1, it matches by name exactly. If dostrcmp is 2, it matches names
 // with case folding.
-func Lookdot1(errnode ir.Node, s *types.Sym, t *types.Type, fs *types.Fields, dostrcmp int) *types.Field {
+func Lookdot1(errnode ir.Node, s *types.Sym, t *types.Type, fs []*types.Field, dostrcmp int) *types.Field {
 	var r *types.Field
-	for _, f := range fs.Slice() {
+	for _, f := range fs {
 		if dostrcmp != 0 && f.Sym.Name == s.Name {
 			return f
 		}
@@ -847,7 +847,7 @@ func Lookdot1(errnode ir.Node, s *types.Sym, t *types.Type, fs *types.Fields, do
 // expression "recv.sym".
 func NewMethodExpr(pos src.XPos, recv *types.Type, sym *types.Sym) *ir.SelectorExpr {
 	// Compute the method set for recv.
-	var ms *types.Fields
+	var ms []*types.Field
 	if recv.IsInterface() {
 		ms = recv.AllMethods()
 	} else {
@@ -1011,8 +1011,9 @@ func nokeys(l ir.Nodes) bool {
 	return true
 }
 
-func hasddd(t *types.Type) bool {
-	for _, tl := range t.Fields().Slice() {
+func hasddd(params []*types.Field) bool {
+	// TODO(mdempsky): Simply check the last param.
+	for _, tl := range params {
 		if tl.IsDDD() {
 			return true
 		}
@@ -1022,7 +1023,7 @@ func hasddd(t *types.Type) bool {
 }
 
 // typecheck assignment: type list = expression list
-func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl ir.Nodes, desc func() string) {
+func typecheckaste(op ir.Op, call ir.Node, isddd bool, params []*types.Field, nl ir.Nodes, desc func() string) {
 	var t *types.Type
 	var i int
 
@@ -1034,9 +1035,9 @@ func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl i
 		n = nl[0]
 	}
 
-	n1 := tstruct.NumFields()
+	n1 := len(params)
 	n2 := len(nl)
-	if !hasddd(tstruct) {
+	if !hasddd(params) {
 		if isddd {
 			goto invalidddd
 		}
@@ -1062,7 +1063,7 @@ func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl i
 	}
 
 	i = 0
-	for _, tl := range tstruct.Fields().Slice() {
+	for _, tl := range params {
 		t = tl.Type
 		if tl.IsDDD() {
 			if isddd {
@@ -1118,98 +1119,12 @@ invalidddd:
 
 notenough:
 	if n == nil || n.Type() != nil {
-		details := errorDetails(nl, tstruct, isddd)
-		if call != nil {
-			// call is the expression being called, not the overall call.
-			// Method expressions have the form T.M, and the compiler has
-			// rewritten those to ONAME nodes but left T in Left.
-			if call.Op() == ir.OMETHEXPR {
-				call := call.(*ir.SelectorExpr)
-				base.Errorf("not enough arguments in call to method expression %v%s", call, details)
-			} else {
-				base.Errorf("not enough arguments in call to %v%s", call, details)
-			}
-		} else {
-			base.Errorf("not enough arguments to %v%s", op, details)
-		}
-		if n != nil {
-			base.Fatalf("invalid call")
-		}
+		base.Fatalf("not enough arguments to %v", op)
 	}
 	return
 
 toomany:
-	details := errorDetails(nl, tstruct, isddd)
-	if call != nil {
-		base.Errorf("too many arguments in call to %v%s", call, details)
-	} else {
-		base.Errorf("too many arguments to %v%s", op, details)
-	}
-}
-
-func errorDetails(nl ir.Nodes, tstruct *types.Type, isddd bool) string {
-	// Suppress any return message signatures if:
-	//
-	// (1) We don't know any type at a call site (see #19012).
-	// (2) Any node has an unknown type.
-	// (3) Invalid type for variadic parameter (see #46957).
-	if tstruct == nil {
-		return "" // case 1
-	}
-
-	if isddd && !nl[len(nl)-1].Type().IsSlice() {
-		return "" // case 3
-	}
-
-	for _, n := range nl {
-		if n.Type() == nil {
-			return "" // case 2
-		}
-	}
-	return fmt.Sprintf("\n\thave %s\n\twant %v", fmtSignature(nl, isddd), tstruct)
-}
-
-// sigrepr is a type's representation to the outside world,
-// in string representations of return signatures
-// e.g in error messages about wrong arguments to return.
-func sigrepr(t *types.Type, isddd bool) string {
-	switch t {
-	case types.UntypedString:
-		return "string"
-	case types.UntypedBool:
-		return "bool"
-	}
-
-	if t.Kind() == types.TIDEAL {
-		// "untyped number" is not commonly used
-		// outside of the compiler, so let's use "number".
-		// TODO(mdempsky): Revisit this.
-		return "number"
-	}
-
-	// Turn []T... argument to ...T for clearer error message.
-	if isddd {
-		if !t.IsSlice() {
-			base.Fatalf("bad type for ... argument: %v", t)
-		}
-		return "..." + t.Elem().String()
-	}
-	return t.String()
-}
-
-// fmtSignature returns the signature of the types at the call or return.
-func fmtSignature(nl ir.Nodes, isddd bool) string {
-	if len(nl) < 1 {
-		return "()"
-	}
-
-	var typeStrings []string
-	for i, n := range nl {
-		isdddArg := isddd && i == len(nl)-1
-		typeStrings = append(typeStrings, sigrepr(n.Type(), isdddArg))
-	}
-
-	return fmt.Sprintf("(%s)", strings.Join(typeStrings, ", "))
+	base.Fatalf("too many arguments to %v", op)
 }
 
 // type check composite.
diff --git a/src/cmd/compile/internal/types/alg.go b/src/cmd/compile/internal/types/alg.go
index 8d56dec824..d3b446213e 100644
--- a/src/cmd/compile/internal/types/alg.go
+++ b/src/cmd/compile/internal/types/alg.go
@@ -103,7 +103,7 @@ func AlgType(t *Type) (AlgKind, *Type) {
 		return ASPECIAL, nil
 
 	case TSTRUCT:
-		fields := t.FieldSlice()
+		fields := t.Fields()
 
 		// One-field struct is same as that one field alone.
 		if len(fields) == 1 && !fields[0].Sym.IsBlank() {
@@ -147,7 +147,7 @@ func IsComparable(t *Type) bool {
 
 // IncomparableField returns an incomparable Field of struct Type t, if any.
 func IncomparableField(t *Type) *Field {
-	for _, f := range t.FieldSlice() {
+	for _, f := range t.Fields() {
 		if !IsComparable(f.Type) {
 			return f
 		}
diff --git a/src/cmd/compile/internal/types/fmt.go b/src/cmd/compile/internal/types/fmt.go
index 0646f43754..7489edd42e 100644
--- a/src/cmd/compile/internal/types/fmt.go
+++ b/src/cmd/compile/internal/types/fmt.go
@@ -452,7 +452,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 			break
 		}
 		b.WriteString("interface {")
-		for i, f := range t.AllMethods().Slice() {
+		for i, f := range t.AllMethods() {
 			if i != 0 {
 				b.WriteByte(';')
 			}
@@ -472,7 +472,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 			}
 			tconv2(b, f.Type, 'S', mode, visited)
 		}
-		if t.AllMethods().Len() != 0 {
+		if len(t.AllMethods()) != 0 {
 			b.WriteByte(' ')
 		}
 		b.WriteByte('}')
@@ -483,12 +483,12 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 		} else {
 			if t.Recv() != nil {
 				b.WriteString("method")
-				tconv2(b, t.Recvs(), 0, mode, visited)
+				tconv2(b, t.recvsTuple(), 0, mode, visited)
 				b.WriteByte(' ')
 			}
 			b.WriteString("func")
 		}
-		tconv2(b, t.Params(), 0, mode, visited)
+		tconv2(b, t.paramsTuple(), 0, mode, visited)
 
 		switch t.NumResults() {
 		case 0:
@@ -496,11 +496,11 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 
 		case 1:
 			b.WriteByte(' ')
-			tconv2(b, t.Results().Field(0).Type, 0, mode, visited) // struct->field->field's type
+			tconv2(b, t.Result(0).Type, 0, mode, visited) // struct->field->field's type
 
 		default:
 			b.WriteByte(' ')
-			tconv2(b, t.Results(), 0, mode, visited)
+			tconv2(b, t.ResultsTuple(), 0, mode, visited)
 		}
 
 	case TSTRUCT:
@@ -532,7 +532,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 				// no argument names on function signature, and no "noescape"/"nosplit" tags
 				fieldVerb = 'S'
 			}
-			for i, f := range t.Fields().Slice() {
+			for i, f := range t.Fields() {
 				if i != 0 {
 					b.WriteString(", ")
 				}
@@ -541,7 +541,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 			b.WriteByte(byte(close))
 		} else {
 			b.WriteString("struct {")
-			for i, f := range t.Fields().Slice() {
+			for i, f := range t.Fields() {
 				if i != 0 {
 					b.WriteByte(';')
 				}
diff --git a/src/cmd/compile/internal/types/identity.go b/src/cmd/compile/internal/types/identity.go
index 6b3bc2ded1..78a644a6dd 100644
--- a/src/cmd/compile/internal/types/identity.go
+++ b/src/cmd/compile/internal/types/identity.go
@@ -92,11 +92,11 @@ cont:
 		return true
 
 	case TINTER:
-		if t1.AllMethods().Len() != t2.AllMethods().Len() {
+		if len(t1.AllMethods()) != len(t2.AllMethods()) {
 			return false
 		}
-		for i, f1 := range t1.AllMethods().Slice() {
-			f2 := t2.AllMethods().Index(i)
+		for i, f1 := range t1.AllMethods() {
+			f2 := t2.AllMethods()[i]
 			if f1.Sym != f2.Sym || !identical(f1.Type, f2.Type, flags, assumedEqual) {
 				return false
 			}
@@ -107,7 +107,7 @@ cont:
 		if t1.NumFields() != t2.NumFields() {
 			return false
 		}
-		for i, f1 := range t1.FieldSlice() {
+		for i, f1 := range t1.Fields() {
 			f2 := t2.Field(i)
 			if f1.Sym != f2.Sym || f1.Embedded != f2.Embedded || !identical(f1.Type, f2.Type, flags, assumedEqual) {
 				return false
@@ -122,9 +122,9 @@ cont:
 		// Check parameters and result parameters for type equality.
 		// We intentionally ignore receiver parameters for type
 		// equality, because they're never relevant.
-		for _, f := range ParamsResults {
+		for _, f := range &ParamsResults {
 			// Loop over fields in structs, ignoring argument names.
-			fs1, fs2 := f(t1).FieldSlice(), f(t2).FieldSlice()
+			fs1, fs2 := f(t1), f(t2)
 			if len(fs1) != len(fs2) {
 				return false
 			}
diff --git a/src/cmd/compile/internal/types/size.go b/src/cmd/compile/internal/types/size.go
index 1c20350128..d0ad2b13d5 100644
--- a/src/cmd/compile/internal/types/size.go
+++ b/src/cmd/compile/internal/types/size.go
@@ -91,7 +91,7 @@ func expandiface(t *Type) {
 	}
 
 	{
-		methods := t.Methods().Slice()
+		methods := t.Methods()
 		sort.SliceStable(methods, func(i, j int) bool {
 			mi, mj := methods[i], methods[j]
 
@@ -110,7 +110,7 @@ func expandiface(t *Type) {
 		})
 	}
 
-	for _, m := range t.Methods().Slice() {
+	for _, m := range t.Methods() {
 		if m.Sym == nil {
 			continue
 		}
@@ -119,7 +119,7 @@ func expandiface(t *Type) {
 		addMethod(m, true)
 	}
 
-	for _, m := range t.Methods().Slice() {
+	for _, m := range t.Methods() {
 		if m.Sym != nil || m.Type == nil {
 			continue
 		}
@@ -133,7 +133,7 @@ func expandiface(t *Type) {
 
 		// Embedded interface: duplicate all methods
 		// and add to t's method set.
-		for _, t1 := range m.Type.AllMethods().Slice() {
+		for _, t1 := range m.Type.AllMethods() {
 			f := NewField(m.Pos, t1.Sym, t1.Type)
 			addMethod(f, false)
 
@@ -173,7 +173,7 @@ func calcStructOffset(errtype *Type, t *Type, o int64, flag int) int64 {
 		maxalign = 8
 	}
 	lastzero := int64(0)
-	for _, f := range t.Fields().Slice() {
+	for _, f := range t.Fields() {
 		if f.Type == nil {
 			// broken field, just skip it so that other valid fields
 			// get a width.
@@ -428,9 +428,9 @@ func CalcSize(t *Type) {
 	// compute their widths as side-effect.
 	case TFUNCARGS:
 		t1 := t.FuncArgs()
-		w = calcStructOffset(t1, t1.Recvs(), 0, 0)
-		w = calcStructOffset(t1, t1.Params(), w, RegSize)
-		w = calcStructOffset(t1, t1.Results(), w, RegSize)
+		w = calcStructOffset(t1, t1.recvsTuple(), 0, 0)
+		w = calcStructOffset(t1, t1.paramsTuple(), w, RegSize)
+		w = calcStructOffset(t1, t1.ResultsTuple(), w, RegSize)
 		t1.extra.(*Func).Argwid = w
 		if w%int64(RegSize) != 0 {
 			base.Warn("bad type %v %d\n", t1, w)
@@ -583,7 +583,7 @@ func PtrDataSize(t *Type) int64 {
 
 	case TSTRUCT:
 		// Find the last field that has pointers, if any.
-		fs := t.Fields().Slice()
+		fs := t.Fields()
 		for i := len(fs) - 1; i >= 0; i-- {
 			if size := PtrDataSize(fs[i].Type); size > 0 {
 				return fs[i].Offset + size
diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index 5f7e6e131d..eafa3f3ef1 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -159,9 +159,9 @@ type Type struct {
 	width int64 // valid if Align > 0
 
 	// list of base methods (excluding embedding)
-	methods Fields
+	methods fields
 	// list of all methods (including embedding)
-	allMethods Fields
+	allMethods fields
 
 	// canonical OTYPE node for a named type (should be an ir.Name node with same sym)
 	obj Object
@@ -316,7 +316,7 @@ func (t *Type) funcType() *Func {
 
 // StructType contains Type fields specific to struct types.
 type Struct struct {
-	fields Fields
+	fields fields
 
 	// Maps have three associated internal structs (see struct MapType).
 	// Map links such structs back to their map type.
@@ -445,39 +445,25 @@ func (f *Field) IsMethod() bool {
 	return f.Type.kind == TFUNC && f.Type.Recv() != nil
 }
 
-// Fields is a pointer to a slice of *Field.
+// fields is a pointer to a slice of *Field.
 // This saves space in Types that do not have fields or methods
 // compared to a simple slice of *Field.
-type Fields struct {
+type fields struct {
 	s *[]*Field
 }
 
-// Len returns the number of entries in f.
-func (f *Fields) Len() int {
-	if f.s == nil {
-		return 0
-	}
-	return len(*f.s)
-}
-
 // Slice returns the entries in f as a slice.
 // Changes to the slice entries will be reflected in f.
-func (f *Fields) Slice() []*Field {
+func (f *fields) Slice() []*Field {
 	if f.s == nil {
 		return nil
 	}
 	return *f.s
 }
 
-// Index returns the i'th element of Fields.
-// It panics if f does not have at least i+1 elements.
-func (f *Fields) Index(i int) *Field {
-	return (*f.s)[i]
-}
-
 // Set sets f to a slice.
 // This takes ownership of the slice.
-func (f *Fields) Set(s []*Field) {
+func (f *fields) Set(s []*Field) {
 	if len(s) == 0 {
 		f.s = nil
 	} else {
@@ -488,14 +474,6 @@ func (f *Fields) Set(s []*Field) {
 	}
 }
 
-// Append appends entries to f.
-func (f *Fields) Append(s ...*Field) {
-	if f.s == nil {
-		f.s = new([]*Field)
-	}
-	*f.s = append(*f.s, s...)
-}
-
 // newType returns a new Type of the specified kind.
 func newType(et Kind) *Type {
 	t := &Type{
@@ -735,10 +713,10 @@ func SubstAny(t *Type, types *[]*Type) *Type {
 		}
 
 	case TFUNC:
-		recvs := SubstAny(t.Recvs(), types)
-		params := SubstAny(t.Params(), types)
-		results := SubstAny(t.Results(), types)
-		if recvs != t.Recvs() || params != t.Params() || results != t.Results() {
+		recvs := SubstAny(t.recvsTuple(), types)
+		params := SubstAny(t.paramsTuple(), types)
+		results := SubstAny(t.ResultsTuple(), types)
+		if recvs != t.recvsTuple() || params != t.paramsTuple() || results != t.ResultsTuple() {
 			t = t.copy()
 			t.funcType().Receiver = recvs
 			t.funcType().Results = results
@@ -749,7 +727,7 @@ func SubstAny(t *Type, types *[]*Type) *Type {
 		// Make a copy of all fields, including ones whose type does not change.
 		// This prevents aliasing across functions, which can lead to later
 		// fields getting their Offset incorrectly overwritten.
-		fields := t.FieldSlice()
+		fields := t.Fields()
 		nfs := make([]*Field, len(fields))
 		for i, f := range fields {
 			nft := SubstAny(f.Type, types)
@@ -757,7 +735,7 @@ func SubstAny(t *Type, types *[]*Type) *Type {
 			nfs[i].Type = nft
 		}
 		t = t.copy()
-		t.SetFields(nfs)
+		t.setFields(nfs)
 	}
 
 	return t
@@ -813,9 +791,22 @@ func (t *Type) wantEtype(et Kind) {
 	}
 }
 
-func (t *Type) Recvs() *Type   { return t.funcType().Receiver }
-func (t *Type) Params() *Type  { return t.funcType().Params }
-func (t *Type) Results() *Type { return t.funcType().Results }
+func (t *Type) recvsTuple() *Type  { return t.funcType().Receiver }
+func (t *Type) paramsTuple() *Type { return t.funcType().Params }
+
+// ResultTuple returns the result type of signature type t as a tuple.
+// This can be used as the type of multi-valued call expressions.
+func (t *Type) ResultsTuple() *Type { return t.funcType().Results }
+
+// Recvs returns a slice of receiver parameters of signature type t.
+// The returned slice always has length 0 or 1.
+func (t *Type) Recvs() []*Field { return t.funcType().Receiver.Fields() }
+
+// Params returns a slice of regular parameters of signature type t.
+func (t *Type) Params() []*Field { return t.funcType().Params.Fields() }
+
+// Results returns a slice of result parameters of signature type t.
+func (t *Type) Results() []*Field { return t.funcType().Results.Fields() }
 
 func (t *Type) NumRecvs() int   { return t.funcType().Receiver.NumFields() }
 func (t *Type) NumParams() int  { return t.funcType().Params.NumFields() }
@@ -824,32 +815,38 @@ func (t *Type) NumResults() int { return t.funcType().Results.NumFields() }
 // IsVariadic reports whether function type t is variadic.
 func (t *Type) IsVariadic() bool {
 	n := t.NumParams()
-	return n > 0 && t.Params().Field(n-1).IsDDD()
+	return n > 0 && t.Param(n-1).IsDDD()
 }
 
 // Recv returns the receiver of function type t, if any.
 func (t *Type) Recv() *Field {
-	s := t.Recvs()
+	s := t.recvsTuple()
 	if s.NumFields() == 0 {
 		return nil
 	}
 	return s.Field(0)
 }
 
+// Param returns the i'th parameter of signature type t.
+func (t *Type) Param(i int) *Field { return t.Params()[i] }
+
+// Result returns the i'th result of signature type t.
+func (t *Type) Result(i int) *Field { return t.Results()[i] }
+
 // RecvsParamsResults stores the accessor functions for a function Type's
 // receiver, parameters, and result parameters, in that order.
 // It can be used to iterate over all of a function's parameter lists.
-var RecvsParamsResults = [3]func(*Type) *Type{
+var RecvsParamsResults = [3]func(*Type) []*Field{
 	(*Type).Recvs, (*Type).Params, (*Type).Results,
 }
 
 // RecvsParams is like RecvsParamsResults, but omits result parameters.
-var RecvsParams = [2]func(*Type) *Type{
+var RecvsParams = [2]func(*Type) []*Field{
 	(*Type).Recvs, (*Type).Params,
 }
 
 // ParamsResults is like RecvsParamsResults, but omits receiver parameters.
-var ParamsResults = [2]func(*Type) *Type{
+var ParamsResults = [2]func(*Type) []*Field{
 	(*Type).Params, (*Type).Results,
 }
 
@@ -898,49 +895,50 @@ func (t *Type) IsFuncArgStruct() bool {
 // Methods returns a pointer to the base methods (excluding embedding) for type t.
 // These can either be concrete methods (for non-interface types) or interface
 // methods (for interface types).
-func (t *Type) Methods() *Fields {
-	return &t.methods
+func (t *Type) Methods() []*Field {
+	return t.methods.Slice()
 }
 
 // AllMethods returns a pointer to all the methods (including embedding) for type t.
 // For an interface type, this is the set of methods that are typically iterated
 // over. For non-interface types, AllMethods() only returns a valid result after
 // CalcMethods() has been called at least once.
-func (t *Type) AllMethods() *Fields {
+func (t *Type) AllMethods() []*Field {
 	if t.kind == TINTER {
 		// Calculate the full method set of an interface type on the fly
 		// now, if not done yet.
 		CalcSize(t)
 	}
-	return &t.allMethods
+	return t.allMethods.Slice()
+}
+
+// SetMethods sets the direct method set for type t (i.e., *not*
+// including promoted methods from embedded types).
+func (t *Type) SetMethods(fs []*Field) {
+	t.methods.Set(fs)
 }
 
-// SetAllMethods sets the set of all methods (including embedding) for type t.
-// Use this method instead of t.AllMethods().Set(), which might call CalcSize() on
-// an uninitialized interface type.
+// SetAllMethods sets the set of all methods for type t (i.e.,
+// including promoted methods from embedded types).
 func (t *Type) SetAllMethods(fs []*Field) {
 	t.allMethods.Set(fs)
 }
 
-// Fields returns the fields of struct type t.
-func (t *Type) Fields() *Fields {
+// fields returns the fields of struct type t.
+func (t *Type) fields() *fields {
 	t.wantEtype(TSTRUCT)
 	return &t.extra.(*Struct).fields
 }
 
 // Field returns the i'th field of struct type t.
-func (t *Type) Field(i int) *Field {
-	return t.Fields().Slice()[i]
-}
+func (t *Type) Field(i int) *Field { return t.Fields()[i] }
 
-// FieldSlice returns a slice of containing all fields of
+// Fields returns a slice of containing all fields of
 // a struct type t.
-func (t *Type) FieldSlice() []*Field {
-	return t.Fields().Slice()
-}
+func (t *Type) Fields() []*Field { return t.fields().Slice() }
 
-// SetFields sets struct type t's fields to fields.
-func (t *Type) SetFields(fields []*Field) {
+// setFields sets struct type t's fields to fields.
+func (t *Type) setFields(fields []*Field) {
 	// If we've calculated the width of t before,
 	// then some other type such as a function signature
 	// might now have the wrong type.
@@ -951,13 +949,13 @@ func (t *Type) SetFields(fields []*Field) {
 		base.Fatalf("SetFields of %v: width previously calculated", t)
 	}
 	t.wantEtype(TSTRUCT)
-	t.Fields().Set(fields)
+	t.fields().Set(fields)
 }
 
 // SetInterface sets the base methods of an interface type t.
 func (t *Type) SetInterface(methods []*Field) {
 	t.wantEtype(TINTER)
-	t.Methods().Set(methods)
+	t.methods.Set(methods)
 }
 
 // ArgWidth returns the total aligned argument size for a function.
@@ -1185,8 +1183,8 @@ func (t *Type) cmp(x *Type) Cmp {
 			return CMPgt // bucket maps are least
 		} // If t != t.Map.Bucket, fall through to general case
 
-		tfs := t.FieldSlice()
-		xfs := x.FieldSlice()
+		tfs := t.Fields()
+		xfs := x.Fields()
 		for i := 0; i < len(tfs) && i < len(xfs); i++ {
 			t1, x1 := tfs[i], xfs[i]
 			if t1.Embedded != x1.Embedded {
@@ -1208,8 +1206,8 @@ func (t *Type) cmp(x *Type) Cmp {
 		return CMPeq
 
 	case TINTER:
-		tfs := t.AllMethods().Slice()
-		xfs := x.AllMethods().Slice()
+		tfs := t.AllMethods()
+		xfs := x.AllMethods()
 		for i := 0; i < len(tfs) && i < len(xfs); i++ {
 			t1, x1 := tfs[i], xfs[i]
 			if c := t1.Sym.cmpsym(x1.Sym); c != CMPeq {
@@ -1225,10 +1223,10 @@ func (t *Type) cmp(x *Type) Cmp {
 		return CMPeq
 
 	case TFUNC:
-		for _, f := range RecvsParamsResults {
+		for _, f := range &RecvsParamsResults {
 			// Loop over fields in structs, ignoring argument names.
-			tfs := f(t).FieldSlice()
-			xfs := f(x).FieldSlice()
+			tfs := f(t)
+			xfs := f(x)
 			for i := 0; i < len(tfs) && i < len(xfs); i++ {
 				ta := tfs[i]
 				tb := xfs[i]
@@ -1397,7 +1395,7 @@ func (t *Type) IsInterface() bool {
 
 // IsEmptyInterface reports whether t is an empty interface type.
 func (t *Type) IsEmptyInterface() bool {
-	return t.IsInterface() && t.AllMethods().Len() == 0
+	return t.IsInterface() && len(t.AllMethods()) == 0
 }
 
 // IsScalar reports whether 't' is a scalar Go type, e.g.
@@ -1422,7 +1420,7 @@ func (t *Type) NumFields() int {
 	if t.kind == TRESULTS {
 		return len(t.extra.(*Results).Types)
 	}
-	return t.Fields().Len()
+	return len(t.Fields())
 }
 func (t *Type) FieldType(i int) *Type {
 	if t.kind == TTUPLE {
@@ -1472,7 +1470,7 @@ func (t *Type) NumComponents(countBlank componentsIncludeBlankFields) int64 {
 			base.Fatalf("NumComponents func arg struct")
 		}
 		var n int64
-		for _, f := range t.FieldSlice() {
+		for _, f := range t.Fields() {
 			if countBlank == IgnoreBlankFields && f.Sym.IsBlank() {
 				continue
 			}
@@ -1741,7 +1739,7 @@ func NewSignature(recv *Field, params, results []*Field) *Type {
 // NewStruct returns a new struct with the given fields.
 func NewStruct(fields []*Field) *Type {
 	t := newType(TSTRUCT)
-	t.SetFields(fields)
+	t.setFields(fields)
 	if fieldsHasShape(fields) {
 		t.SetHasShape(true)
 	}
@@ -1790,7 +1788,7 @@ func IsReflexive(t *Type) bool {
 		return IsReflexive(t.Elem())
 
 	case TSTRUCT:
-		for _, t1 := range t.Fields().Slice() {
+		for _, t1 := range t.Fields() {
 			if !IsReflexive(t1.Type) {
 				return false
 			}
diff --git a/src/cmd/compile/internal/walk/assign.go b/src/cmd/compile/internal/walk/assign.go
index a7d58f11ab..a147b15e57 100644
--- a/src/cmd/compile/internal/walk/assign.go
+++ b/src/cmd/compile/internal/walk/assign.go
@@ -170,11 +170,11 @@ func walkAssignMapRead(init *ir.Nodes, n *ir.AssignListStmt) ir.Node {
 	var call *ir.CallExpr
 	if w := t.Elem().Size(); w <= zeroValSize {
 		fn := mapfn(mapaccess2[fast], t, false)
-		call = mkcall1(fn, fn.Type().Results(), init, reflectdata.IndexMapRType(base.Pos, r), r.X, key)
+		call = mkcall1(fn, fn.Type().ResultsTuple(), init, reflectdata.IndexMapRType(base.Pos, r), r.X, key)
 	} else {
 		fn := mapfn("mapaccess2_fat", t, true)
 		z := reflectdata.ZeroAddr(w)
-		call = mkcall1(fn, fn.Type().Results(), init, reflectdata.IndexMapRType(base.Pos, r), r.X, key, z)
+		call = mkcall1(fn, fn.Type().ResultsTuple(), init, reflectdata.IndexMapRType(base.Pos, r), r.X, key, z)
 	}
 
 	// mapaccess2* returns a typed bool, but due to spec changes,
@@ -230,7 +230,7 @@ func walkReturn(n *ir.ReturnStmt) ir.Node {
 		return n
 	}
 
-	results := fn.Type().Results().FieldSlice()
+	results := fn.Type().Results()
 	dsts := make([]ir.Node, len(results))
 	for i, v := range results {
 		// TODO(mdempsky): typecheck should have already checked the result variables.
diff --git a/src/cmd/compile/internal/walk/builtin.go b/src/cmd/compile/internal/walk/builtin.go
index 9f3102cf30..11951179a5 100644
--- a/src/cmd/compile/internal/walk/builtin.go
+++ b/src/cmd/compile/internal/walk/builtin.go
@@ -663,7 +663,7 @@ func walkPrint(nn *ir.CallExpr, init *ir.Nodes) ir.Node {
 		}
 
 		r := ir.NewCallExpr(base.Pos, ir.OCALL, on, nil)
-		if params := on.Type().Params().FieldSlice(); len(params) > 0 {
+		if params := on.Type().Params(); len(params) > 0 {
 			t := params[0].Type
 			n = typecheck.Conv(n, t)
 			r.Args.Append(n)
@@ -757,7 +757,7 @@ func walkUnsafeSlice(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
 		mem := typecheck.TempAt(base.Pos, ir.CurFunc, types.Types[types.TUINTPTR])
 		overflow := typecheck.TempAt(base.Pos, ir.CurFunc, types.Types[types.TBOOL])
 		fn := typecheck.LookupRuntime("mulUintptr")
-		call := mkcall1(fn, fn.Type().Results(), init, ir.NewInt(base.Pos, sliceType.Elem().Size()), typecheck.Conv(typecheck.Conv(len, lenType), types.Types[types.TUINTPTR]))
+		call := mkcall1(fn, fn.Type().ResultsTuple(), init, ir.NewInt(base.Pos, sliceType.Elem().Size()), typecheck.Conv(typecheck.Conv(len, lenType), types.Types[types.TUINTPTR]))
 		appendWalkStmt(init, ir.NewAssignListStmt(base.Pos, ir.OAS2, []ir.Node{mem, overflow}, []ir.Node{call}))
 
 		// if overflow || mem > -uintptr(ptr) {
diff --git a/src/cmd/compile/internal/walk/closure.go b/src/cmd/compile/internal/walk/closure.go
index 27eebf4144..ca8adb5943 100644
--- a/src/cmd/compile/internal/walk/closure.go
+++ b/src/cmd/compile/internal/walk/closure.go
@@ -67,7 +67,7 @@ func directClosureCall(n *ir.CallExpr) {
 
 	// Create new function type with parameters prepended, and
 	// then update type and declarations.
-	typ = types.NewSignature(nil, append(params, typ.Params().FieldSlice()...), typ.Results().FieldSlice())
+	typ = types.NewSignature(nil, append(params, typ.Params()...), typ.Results())
 	f.SetType(typ)
 	clofn.Dcl = append(decls, clofn.Dcl...)
 
@@ -80,9 +80,9 @@ func directClosureCall(n *ir.CallExpr) {
 	// node, but we only rewrote the ONAME node's type. Logically,
 	// they're the same, but the stack offsets probably changed.
 	if typ.NumResults() == 1 {
-		n.SetType(typ.Results().Field(0).Type)
+		n.SetType(typ.Result(0).Type)
 	} else {
-		n.SetType(typ.Results())
+		n.SetType(typ.ResultsTuple())
 	}
 
 	// Add to Closures for enqueueFunc. It's no longer a proper
diff --git a/src/cmd/compile/internal/walk/expr.go b/src/cmd/compile/internal/walk/expr.go
index 5fb2e3a6f5..85a6d1fc33 100644
--- a/src/cmd/compile/internal/walk/expr.go
+++ b/src/cmd/compile/internal/walk/expr.go
@@ -608,7 +608,7 @@ func walkCall1(n *ir.CallExpr, init *ir.Nodes) {
 
 	for i, arg := range args {
 		// Validate argument and parameter types match.
-		param := params.Field(i)
+		param := params[i]
 		if !types.Identical(arg.Type(), param.Type) {
 			base.FatalfAt(n.Pos(), "assigning %L to parameter %v (type %v)", arg, param.Sym, param.Type)
 		}
@@ -977,14 +977,14 @@ func usemethod(n *ir.CallExpr) {
 	}
 
 	t := dot.Selection.Type
-	if t.NumParams() != 1 || t.Params().Field(0).Type.Kind() != pKind {
+	if t.NumParams() != 1 || t.Param(0).Type.Kind() != pKind {
 		return
 	}
 	switch t.NumResults() {
 	case 1:
 		// ok
 	case 2:
-		if t.Results().Field(1).Type.Kind() != types.TBOOL {
+		if t.Result(1).Type.Kind() != types.TBOOL {
 			return
 		}
 	default:
@@ -993,7 +993,7 @@ func usemethod(n *ir.CallExpr) {
 
 	// Check that first result type is "reflect.Method". Note that we have to check sym name and sym package
 	// separately, as we can't check for exact string "reflect.Method" reliably (e.g., see #19028 and #38515).
-	if s := t.Results().Field(0).Type.Sym(); s != nil && s.Name == "Method" && types.IsReflectPkg(s.Pkg) {
+	if s := t.Result(0).Type.Sym(); s != nil && s.Name == "Method" && types.IsReflectPkg(s.Pkg) {
 		ir.CurFunc.SetReflectMethod(true)
 		// The LSym is initialized at this point. We need to set the attribute on the LSym.
 		ir.CurFunc.LSym.Set(obj.AttrReflectMethod, true)
diff --git a/src/cmd/compile/internal/walk/range.go b/src/cmd/compile/internal/walk/range.go
index dd2f346c5f..8bf1c5b0f9 100644
--- a/src/cmd/compile/internal/walk/range.go
+++ b/src/cmd/compile/internal/walk/range.go
@@ -327,7 +327,7 @@ func walkRange(nrange *ir.RangeStmt) ir.Node {
 		// } else {
 		// hv2, hv1 = decoderune(ha, hv1)
 		fn := typecheck.LookupRuntime("decoderune")
-		call := mkcall1(fn, fn.Type().Results(), &nif.Else, ha, hv1)
+		call := mkcall1(fn, fn.Type().ResultsTuple(), &nif.Else, ha, hv1)
 		a := ir.NewAssignListStmt(base.Pos, ir.OAS2, []ir.Node{hv2, hv1}, []ir.Node{call})
 		nif.Else.Append(a)
 
diff --git a/src/cmd/compile/internal/walk/select.go b/src/cmd/compile/internal/walk/select.go
index 009753c8ad..ca6a76ad00 100644
--- a/src/cmd/compile/internal/walk/select.go
+++ b/src/cmd/compile/internal/walk/select.go
@@ -128,7 +128,7 @@ func walkSelectCases(cases []*ir.CommClause) []ir.Node {
 			}
 			cond = typecheck.TempAt(base.Pos, ir.CurFunc, types.Types[types.TBOOL])
 			fn := chanfn("selectnbrecv", 2, ch.Type())
-			call := mkcall1(fn, fn.Type().Results(), r.PtrInit(), elem, ch)
+			call := mkcall1(fn, fn.Type().ResultsTuple(), r.PtrInit(), elem, ch)
 			as := ir.NewAssignListStmt(r.Pos(), ir.OAS2, []ir.Node{cond, n.Lhs[1]}, []ir.Node{call})
 			r.PtrInit().Append(typecheck.Stmt(as))
 		}
@@ -227,7 +227,7 @@ func walkSelectCases(cases []*ir.CommClause) []ir.Node {
 	r.Lhs = []ir.Node{chosen, recvOK}
 	fn := typecheck.LookupRuntime("selectgo")
 	var fnInit ir.Nodes
-	r.Rhs = []ir.Node{mkcall1(fn, fn.Type().Results(), &fnInit, bytePtrToIndex(selv, 0), bytePtrToIndex(order, 0), pc0, ir.NewInt(base.Pos, int64(nsends)), ir.NewInt(base.Pos, int64(nrecvs)), ir.NewBool(base.Pos, dflt == nil))}
+	r.Rhs = []ir.Node{mkcall1(fn, fn.Type().ResultsTuple(), &fnInit, bytePtrToIndex(selv, 0), bytePtrToIndex(order, 0), pc0, ir.NewInt(base.Pos, int64(nsends)), ir.NewInt(base.Pos, int64(nrecvs)), ir.NewBool(base.Pos, dflt == nil))}
 	init = append(init, fnInit...)
 	init = append(init, typecheck.Stmt(r))