cmd/compile/internal/types: remove Markdcl/Pushdcl/Popdcl

Sym.Def used to be used for symbol resolution during the
old (pre-types2) typechecker. But since moving to types2-based IR
construction, we haven't really had a need for Sym.Def to ever refer
to anything but the package-scope definition, because types2 handles
symbol resolution for us.

This CL finally removes the Markdcl/Pushdcl/Popdcl functions that have
been a recurring source of issues in the past.

Change-Id: I2b012a0f17203efdd724ebd1e9314bd128cc2d61
Reviewed-on: https://go-review.googlesource.com/c/go/+/458625
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>

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

@@ -19,7 +19,6 @@ type DebugFlags struct {
 	Append                int    `help:"print information about append compilation"`
 	Checkptr              int    `help:"instrument unsafe pointer conversions\n0: instrumentation disabled\n1: conversions involving unsafe.Pointer are instrumented\n2: conversions to unsafe.Pointer force heap allocation" concurrent:"ok"`
 	Closure               int    `help:"print information about closure compilation"`
-	DclStack              int    `help:"run internal dclstack check"`
 	Defer                 int    `help:"print information about defer compilation"`
 	DisableNil            int    `help:"disable nil checks" concurrent:"ok"`
 	DumpPtrs              int    `help:"show Node pointers values in dump output"`

src/cmd/compile/internal/reflectdata/alg.go

@@ -224,10 +224,6 @@ func genhash(t *types.Type) *obj.LSym {
 	typecheck.Stmts(fn.Body)
 	ir.CurFunc = nil
 
-	if base.Debug.DclStack != 0 {
-		types.CheckDclstack()
-	}
-
 	fn.SetNilCheckDisabled(true)
 	typecheck.Target.Decls = append(typecheck.Target.Decls, fn)
 
@@ -552,10 +548,6 @@ func geneq(t *types.Type) *obj.LSym {
 	typecheck.Stmts(fn.Body)
 	ir.CurFunc = nil
 
-	if base.Debug.DclStack != 0 {
-		types.CheckDclstack()
-	}
-
 	// Disable checknils while compiling this code.
 	// We are comparing a struct or an array,
 	// neither of which can be nil, and our comparisons

src/cmd/compile/internal/ssagen/abi.go

@@ -324,9 +324,6 @@ func makeABIWrapper(f *ir.Func, wrapperABI obj.ABI) {
 	fn.Body.Append(tail)
 
 	typecheck.FinishFuncBody()
-	if base.Debug.DclStack != 0 {
-		types.CheckDclstack()
-	}
 
 	typecheck.Func(fn)
 	ir.CurFunc = fn

src/cmd/compile/internal/typecheck/dcl.go

@@ -59,6 +59,7 @@ func Declare(n *ir.Name, ctxt ir.Class) {
 			base.ErrorfAt(n.Pos(), "cannot declare main - must be func")
 		}
 		Target.Externs = append(Target.Externs, n)
+		s.Def = n
 	} else {
 		if ir.CurFunc == nil && ctxt == ir.PAUTO {
 			base.Pos = n.Pos()
@@ -67,7 +68,6 @@ func Declare(n *ir.Name, ctxt ir.Class) {
 		if ir.CurFunc != nil && ctxt != ir.PFUNC && n.Op() == ir.ONAME {
 			ir.CurFunc.Dcl = append(ir.CurFunc.Dcl, n)
 		}
-		types.Pushdcl(s)
 		n.Curfn = ir.CurFunc
 	}
 
@@ -75,7 +75,6 @@ func Declare(n *ir.Name, ctxt ir.Class) {
 		n.SetFrameOffset(0)
 	}
 
-	s.Def = n
 	n.Class = ctxt
 	if ctxt == ir.PFUNC {
 		n.Sym().SetFunc(true)
@@ -107,8 +106,6 @@ func StartFuncBody(fn *ir.Func) {
 	funcStack = append(funcStack, funcStackEnt{ir.CurFunc, DeclContext})
 	ir.CurFunc = fn
 	DeclContext = ir.PAUTO
-
-	types.Markdcl()
 }
 
 // finish the body.
@@ -116,7 +113,6 @@ func StartFuncBody(fn *ir.Func) {
 // returns in extern-declaration context.
 func FinishFuncBody() {
 	// change the declaration context from auto to previous context
-	types.Popdcl()
 	var e funcStackEnt
 	funcStack, e = funcStack[:len(funcStack)-1], funcStack[len(funcStack)-1]
 	ir.CurFunc, DeclContext = e.curfn, e.dclcontext

src/cmd/compile/internal/types/scope.go

@@ -4,96 +4,8 @@
 
 package types
 
-import (
-	"cmd/compile/internal/base"
-)
-
-// Declaration stack & operations
-
-// A dsym stores a symbol's shadowed declaration so that it can be
-// restored once the block scope ends.
-type dsym struct {
-	sym *Sym // sym == nil indicates stack mark
-	def Object
-}
-
-// dclstack maintains a stack of shadowed symbol declarations so that
-// Popdcl can restore their declarations when a block scope ends.
-var dclstack []dsym
-
-// Pushdcl pushes the current declaration for symbol s (if any) so that
-// it can be shadowed by a new declaration within a nested block scope.
-func Pushdcl(s *Sym) {
-	dclstack = append(dclstack, dsym{
-		sym: s,
-		def: s.Def,
-	})
-}
-
-// Popdcl pops the innermost block scope and restores all symbol declarations
-// to their previous state.
-func Popdcl() {
-	for i := len(dclstack); i > 0; i-- {
-		d := &dclstack[i-1]
-		s := d.sym
-		if s == nil {
-			// pop stack mark
-			dclstack = dclstack[:i-1]
-			return
-		}
-
-		s.Def = d.def
-
-		// Clear dead pointer fields.
-		d.sym = nil
-		d.def = nil
-	}
-	base.Fatalf("popdcl: no stack mark")
-}
-
-// Markdcl records the start of a new block scope for declarations.
-func Markdcl() {
-	dclstack = append(dclstack, dsym{
-		sym: nil, // stack mark
-	})
-}
-
-func isDclstackValid() bool {
-	for _, d := range dclstack {
-		if d.sym == nil {
-			return false
-		}
-	}
-	return true
-}
-
 // PkgDef returns the definition associated with s at package scope.
-func (s *Sym) PkgDef() Object {
-	return *s.pkgDefPtr()
-}
+func (s *Sym) PkgDef() Object { return s.Def }
 
 // SetPkgDef sets the definition associated with s at package scope.
-func (s *Sym) SetPkgDef(n Object) {
-	*s.pkgDefPtr() = n
-}
-
-func (s *Sym) pkgDefPtr() *Object {
-	// Look for outermost saved declaration, which must be the
-	// package scope definition, if present.
-	for i := range dclstack {
-		d := &dclstack[i]
-		if s == d.sym {
-			return &d.def
-		}
-	}
-
-	// Otherwise, the declaration hasn't been shadowed within a
-	// function scope.
-	return &s.Def
-}
-
-func CheckDclstack() {
-	if !isDclstackValid() {
-		base.Fatalf("mark left on the dclstack")
-	}
-}
+func (s *Sym) SetPkgDef(n Object) { s.Def = n }

src/cmd/compile/internal/types/sym.go

@@ -35,8 +35,6 @@ type Sym struct {
 	// bound to within the current scope. (Most parts of the compiler should
 	// prefer passing the Node directly, rather than relying on this field.)
 	//
-	// Def is saved and restored by Pushdcl/Popdcl.
-	//
 	// Deprecated: New code should avoid depending on Sym.Def. Add
 	// mdempsky@ as a reviewer for any CLs involving Sym.Def.
 	Def Object