[dev.regabi] cmd/compile: change ir.NameOffsetExpr to use *obj.LSym instead of *Name

Because NameOffsetExpr is always used with global variables, and SSA
backend only needs (*Name).Linksym() to generate value for them.

Passes toolstash -cmp.

Updates #43737

Change-Id: I17209e21383edb766070c0accd1fa4660659caef
Reviewed-on: https://go-review.googlesource.com/c/go/+/284119
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/ir/expr.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/types"
+	"cmd/internal/obj"
 	"cmd/internal/src"
 	"fmt"
 	"go/constant"
@@ -461,22 +462,26 @@ func NewResultExpr(pos src.XPos, typ *types.Type, offset int64) *ResultExpr {
 	return n
 }
 
-// A NameOffsetExpr refers to an offset within a variable.
+// A NameOffsetExpr refers to an offset within a global variable.
 // It is like a SelectorExpr but without the field name.
 type NameOffsetExpr struct {
 	miniExpr
-	Name_   *Name
+	Linksym *obj.LSym
 	Offset_ int64
 }
 
+func NewLinksymOffsetExpr(pos src.XPos, lsym *obj.LSym, offset int64, typ *types.Type) *NameOffsetExpr {
+	n := &NameOffsetExpr{Linksym: lsym, Offset_: offset}
+	n.typ = typ
+	n.op = ONAMEOFFSET
+	return n
+}
+
 func NewNameOffsetExpr(pos src.XPos, name *Name, offset int64, typ *types.Type) *NameOffsetExpr {
 	if name == nil || IsBlank(name) || !(name.Op() == ONAME && name.Class == PEXTERN) {
 		base.FatalfAt(pos, "cannot take offset of nil, blank name or non-global variable: %v", name)
 	}
-	n := &NameOffsetExpr{Name_: name, Offset_: offset}
+	return NewLinksymOffsetExpr(pos, name.Linksym(), offset, typ)
-	n.typ = typ
-	n.op = ONAMEOFFSET
-	return n
 }
 
 // A SelectorExpr is a selector expression X.Sel.

src/cmd/compile/internal/ir/fmt.go

@@ -634,7 +634,7 @@ func exprFmt(n Node, s fmt.State, prec int) {
 
 	case ONAMEOFFSET:
 		n := n.(*NameOffsetExpr)
-		fmt.Fprintf(s, "(%v)(%v@%d)", n.Type(), n.Name_, n.Offset_)
+		fmt.Fprintf(s, "(%v)(%s@%d)", n.Type(), n.Linksym.Name, n.Offset_)
 
 	case OTYPE:
 		if n.Type() == nil && n.Sym() != nil {

src/cmd/compile/internal/ir/node_gen.go

@@ -825,16 +825,10 @@ func (n *NameOffsetExpr) doChildren(do func(Node) bool) bool {
 	if doNodes(n.init, do) {
 		return true
 	}
-	if n.Name_ != nil && do(n.Name_) {
-		return true
-	}
 	return false
 }
 func (n *NameOffsetExpr) editChildren(edit func(Node) Node) {
 	editNodes(n.init, edit)
-	if n.Name_ != nil {
-		n.Name_ = edit(n.Name_).(*Name)
-	}
 }
 
 func (n *NilExpr) Format(s fmt.State, verb rune) { fmtNode(n, s, verb) }

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

@@ -2257,15 +2257,10 @@ func (s *state) expr(n ir.Node) *ssa.Value {
 		if s.canSSA(n) {
 			return s.variable(n, n.Type())
 		}
-		addr := s.addr(n)
+		return s.load(n.Type(), s.addr(n))
-		return s.load(n.Type(), addr)
 	case ir.ONAMEOFFSET:
 		n := n.(*ir.NameOffsetExpr)
-		if s.canSSAName(n.Name_) && TypeOK(n.Type()) {
+		return s.load(n.Type(), s.addr(n))
-			return s.variable(n, n.Type())
-		}
-		addr := s.addr(n)
-		return s.load(n.Type(), addr)
 	case ir.ONIL:
 		n := n.(*ir.NilExpr)
 		t := n.Type()
@@ -5088,13 +5083,18 @@ func (s *state) addr(n ir.Node) *ssa.Value {
 	}
 
 	t := types.NewPtr(n.Type())
-	var offset int64
+	linksymOffset := func(lsym *obj.LSym, offset int64) *ssa.Value {
+		v := s.entryNewValue1A(ssa.OpAddr, t, lsym, s.sb)
+		// TODO: Make OpAddr use AuxInt as well as Aux.
+		if offset != 0 {
+			v = s.entryNewValue1I(ssa.OpOffPtr, v.Type, offset, v)
+		}
+		return v
+	}
 	switch n.Op() {
 	case ir.ONAMEOFFSET:
 		no := n.(*ir.NameOffsetExpr)
-		offset = no.Offset_
+		return linksymOffset(no.Linksym, no.Offset_)
-		n = no.Name_
-		fallthrough
 	case ir.ONAME:
 		n := n.(*ir.Name)
 		if n.Heapaddr != nil {
@@ -5103,12 +5103,7 @@ func (s *state) addr(n ir.Node) *ssa.Value {
 		switch n.Class {
 		case ir.PEXTERN:
 			// global variable
-			v := s.entryNewValue1A(ssa.OpAddr, t, n.Linksym(), s.sb)
+			return linksymOffset(n.Linksym(), 0)
-			// TODO: Make OpAddr use AuxInt as well as Aux.
-			if offset != 0 {
-				v = s.entryNewValue1I(ssa.OpOffPtr, v.Type, offset, v)
-			}
-			return v
 		case ir.PPARAM:
 			// parameter slot
 			v := s.decladdrs[n]