cmd/compile/internal/types: remove Sym.Block and Sym.Lastlineno

These fields were used for tracking the last scope/position that an
identifier was declared, so that we could report redeclaration
errors. However, redeclaration errors are now diagnosed by types2 (and
typecheck.Redeclared was removed in CL 388537), so these fields can be
safely pruned.

Updates #51691.

Change-Id: Ifd5ea3f6795fadb420913298d59287c95e4669a1
Reviewed-on: https://go-review.googlesource.com/c/go/+/394276
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -70,8 +70,6 @@ func Declare(n *ir.Name, ctxt ir.Class) {
 		n.SetFrameOffset(0)
 	}
 
-	s.Block = types.Block
-	s.Lastlineno = base.Pos
 	s.Def = n
 	n.Class = ctxt
 	if ctxt == ir.PFUNC {

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

@@ -67,7 +67,6 @@ func Lookup(name string) *types.Sym {
 // but does not make them visible to user code.
 func InitRuntime() {
 	base.Timer.Start("fe", "loadsys")
-	types.Block = 1
 
 	typs := runtimeTypes()
 	for _, d := range &runtimeDecls {

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

@@ -91,14 +91,12 @@ func InitUniverse() {
 
 	s = Lookup("_")
 	types.BlankSym = s
-	s.Block = -100
 	s.Def = NewName(s)
 	ir.AsNode(s.Def).SetType(types.Types[types.TBLANK])
 	ir.BlankNode = ir.AsNode(s.Def)
 	ir.BlankNode.SetTypecheck(1)
 
 	s = types.BuiltinPkg.Lookup("_")
-	s.Block = -100
 	s.Def = NewName(s)
 	ir.AsNode(s.Def).SetType(types.Types[types.TBLANK])
 
@@ -222,6 +220,5 @@ func DeclareUniverse() {
 		}
 
 		s1.Def = s.Def
-		s1.Block = s.Block
 	}
 }

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

@@ -6,21 +6,15 @@ package types
 
 import (
 	"cmd/compile/internal/base"
-	"cmd/internal/src"
 )
 
 // Declaration stack & operations
 
-var blockgen int32 = 1 // max block number
-var Block int32 = 1    // current block number
-
 // 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
-	block      int32
-	lastlineno src.XPos // last declaration for diagnostic
+	sym *Sym // sym == nil indicates stack mark
+	def Object
 }
 
 // dclstack maintains a stack of shadowed symbol declarations so that
@@ -31,10 +25,8 @@ var dclstack []dsym
 // 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,
-		block:      s.Block,
-		lastlineno: s.Lastlineno,
+		sym: s,
+		def: s.Def,
 	})
 }
 
@@ -46,14 +38,11 @@ func Popdcl() {
 		s := d.sym
 		if s == nil {
 			// pop stack mark
-			Block = d.block
 			dclstack = dclstack[:i-1]
 			return
 		}
 
 		s.Def = d.def
-		s.Block = d.block
-		s.Lastlineno = d.lastlineno
 
 		// Clear dead pointer fields.
 		d.sym = nil
@@ -65,11 +54,8 @@ func Popdcl() {
 // Markdcl records the start of a new block scope for declarations.
 func Markdcl() {
 	dclstack = append(dclstack, dsym{
-		sym:   nil, // stack mark
-		block: Block,
+		sym: nil, // stack mark
 	})
-	blockgen++
-	Block = blockgen
 }
 
 func isDclstackValid() bool {

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

@@ -20,7 +20,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Sym{}, 44, 72},
+		{Sym{}, 32, 64},
 		{Type{}, 64, 112},
 		{Map{}, 20, 40},
 		{Forward{}, 20, 32},

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

@@ -7,7 +7,6 @@ package types
 import (
 	"cmd/compile/internal/base"
 	"cmd/internal/obj"
-	"cmd/internal/src"
 	"unicode"
 	"unicode/utf8"
 )
@@ -32,14 +31,15 @@ type Sym struct {
 	Pkg  *Pkg
 	Name string // object name
 
-	// Def, Block, and Lastlineno are saved and restored by Pushdcl/Popdcl.
-
 	// The unique ONAME, OTYPE, OPACK, or OLITERAL node that this symbol is
 	// bound to within the current scope. (Most parts of the compiler should
 	// prefer passing the Node directly, rather than relying on this field.)
-	Def        Object
-	Block      int32    // blocknumber to catch redeclaration
-	Lastlineno src.XPos // last declaration for diagnostic
+	//
+	// 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
 
 	flags bitset8
 }