cmd/compile/internal/types: remove Sym.Link field

The dclstack is now a proper stack and thus we can implement it
using a slice rather than a linked list.

Change-Id: I200e85621ff76c111bdeb7eb382fd82da438f3ba
Reviewed-on: https://go-review.googlesource.com/41135
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/compile/internal/types/scope.go b/src/cmd/compile/internal/types/scope.go
index 67de273f252db8c0ab504b1d5e2eac370713deaf..80e87eb4868877e410a9c606467e0ecade745fcf 100644 (file)
--- a/src/cmd/compile/internal/types/scope.go
+++ b/src/cmd/compile/internal/types/scope.go
@@ -4,10 +4,7 @@
 
 package types
 
-import (
-       "cmd/internal/src"
-       "fmt"
-)
+import "cmd/internal/src"
 
 // Declaration stack & operations
 
@@ -16,17 +13,11 @@ var Block int32        // current block number
 
 // dclstack maintains a stack of shadowed symbol declarations so that
 // popdcl can restore their declarations when a block scope ends.
-// The stack is maintained as a linked list, using Sym's Link field.
 //
-// In practice, the "stack" actually ends up forming a tree: goto and label
-// statements record the current state of dclstack so that checkgoto can
-// validate that a goto statement does not jump over any declarations or
-// into a new block scope.
-//
-// Finally, the Syms in this list are not "real" Syms as they don't actually
+// The Syms on this stack are not "real" Syms as they don't actually
 // represent object names. Sym is just a convenient type for saving shadowed
 // Sym definitions, and only a subset of its fields are actually used.
-var dclstack *Sym
+var dclstack []*Sym
 
 func dcopy(a, b *Sym) {
        a.Pkg = b.Pkg
@@ -39,8 +30,7 @@ func dcopy(a, b *Sym) {
 func push(pos src.XPos) *Sym {
        d := new(Sym)
        d.Lastlineno = pos
-       d.Link = dclstack
-       dclstack = d
+       dclstack = append(dclstack, d)
        return d
 }
 
@@ -54,48 +44,38 @@ func Pushdcl(s *Sym, pos src.XPos) {
 // Popdcl pops the innermost block scope and restores all symbol declarations
 // to their previous state.
 func Popdcl() {
-       d := dclstack
-       for ; d != nil && d.Name != ""; d = d.Link {
+       i := len(dclstack)
+       for ; i > 0; i-- {
+               d := dclstack[i-1]
+               if d.Name == "" {
+                       break
+               }
                s := d.Pkg.Lookup(d.Name)
                lno := s.Lastlineno
                dcopy(s, d)
                d.Lastlineno = lno
        }
 
-       if d == nil {
+       if i == 0 {
                Fatalf("popdcl: no mark")
        }
 
-       dclstack = d.Link // pop mark
-       Block = d.Block
+       Block = dclstack[i-1].Block
+       dclstack = dclstack[:i-1] // pop mark
 }
 
 // Markdcl records the start of a new block scope for declarations.
 func Markdcl(lineno src.XPos) {
        d := push(lineno)
-       d.Name = "" // used as a mark in fifo
+       d.Name = "" // used as stack mark
        d.Block = Block
 
        blockgen++
        Block = blockgen
 }
 
-// keep around for debugging
-func DumpDclstack() {
-       i := 0
-       for d := dclstack; d != nil; d = d.Link {
-               fmt.Printf("%6d  %p", i, d)
-               if d.Name != "" {
-                       fmt.Printf("  '%s'  %v\n", d.Name, d.Pkg.Lookup(d.Name))
-               } else {
-                       fmt.Printf("  ---\n")
-               }
-               i++
-       }
-}
-
 func IsDclstackValid() bool {
-       for d := dclstack; d != nil; d = d.Link {
+       for _, d := range dclstack {
                if d.Name == "" {
                        return false
                }

diff --git a/src/cmd/compile/internal/types/sizeof_test.go b/src/cmd/compile/internal/types/sizeof_test.go
index e3fa76169285412c084b2d92ba3a02f1629b6cfb..d31e169b00e639de1ba8f8597c8a9945788bc87b 100644 (file)
--- a/src/cmd/compile/internal/types/sizeof_test.go
+++ b/src/cmd/compile/internal/types/sizeof_test.go
@@ -22,7 +22,7 @@ func TestSizeof(t *testing.T) {
                _32bit uintptr     // size on 32bit platforms
                _64bit uintptr     // size on 64bit platforms
        }{
-               {Sym{}, 60, 104},
+               {Sym{}, 56, 96},
                {Type{}, 52, 88},
                {Map{}, 20, 40},
                {Forward{}, 20, 32},

diff --git a/src/cmd/compile/internal/types/sym.go b/src/cmd/compile/internal/types/sym.go
index 1086b99fddccf5ca604cbf8a45782d644a9eba47..af6eccc485ee3092b1a070a94ee4fc4737e2a148 100644 (file)
--- a/src/cmd/compile/internal/types/sym.go
+++ b/src/cmd/compile/internal/types/sym.go
@@ -18,7 +18,6 @@ import (
 // allows using Sym pointer equality to test for Go identifier uniqueness when
 // handling selector expressions.
 type Sym struct {
-       Link      *Sym
        Importdef *Pkg   // where imported definition was found
        Linkname  string // link name