cmd/internal/gc: clean up Componentgen

Update #9855

In preparation for introducing direct use of a zero register on
platforms that support it, take the opportunity to clean up
Componentgen a bit.

Change-Id: I120ce1ffcca8c4f7603bfe76bfa1aedd27ebb4d2
Reviewed-on: https://go-review.googlesource.com/8691
Run-TryBot: Dave Cheney <dave@cheney.net>
Reviewed-by: Minux Ma <minux@golang.org>

diff --git a/src/cmd/internal/gc/gen.go b/src/cmd/internal/gc/gen.go
index 4b7344a4954f5113186f853cb40c91012a7a70f4..fde0a196b713fd2d2439057915c89604a19038d0 100644 (file)
--- a/src/cmd/internal/gc/gen.go
+++ b/src/cmd/internal/gc/gen.go
@@ -1116,26 +1116,16 @@ func checklabels() {
        }
 }
 
-/*
- * copy a composite value by moving its individual components.
- * Slices, strings and interfaces are supported.
- * Small structs or arrays with elements of basic type are
- * also supported.
- * nr is N when assigning a zero value.
- * return 1 if can do, 0 if can't.
- */
+// Componentgen copies a composite value by moving its individual components.
+// Slices, strings and interfaces are supported. Small structs or arrays with
+// elements of basic type are also supported.
+// nr is nil when assigning a zero value.
 func Componentgen(nr *Node, nl *Node) bool {
-       var nodl Node
-       var nodr Node
-
-       freel := 0
-       freer := 0
-
-       var isConstString bool
+       var nodl, nodr Node
 
        switch nl.Type.Etype {
        default:
-               goto no
+               return false
 
        case TARRAY:
                t := nl.Type
@@ -1150,16 +1140,16 @@ func Componentgen(nr *Node, nl *Node) bool {
                        break
                }
 
-               goto no
+               return false
 
-               // Small structs with non-fat types are ok.
-       // Zero-sized structs are treated separately elsewhere.
        case TSTRUCT:
+               // Small structs with non-fat types are ok.
+               // Zero-sized structs are treated separately elsewhere.
                fldcount := int64(0)
 
                for t := nl.Type.Type; t != nil; t = t.Down {
                        if Isfat(t.Type) && !Isslice(t) {
-                               goto no
+                               return false
                        }
                        if t.Etype != TFIELD {
                                Fatal("componentgen: not a TFIELD: %v", Tconv(t, obj.FmtLong))
@@ -1168,28 +1158,28 @@ func Componentgen(nr *Node, nl *Node) bool {
                }
 
                if fldcount == 0 || fldcount > 4 {
-                       goto no
+                       return false
                }
 
        case TSTRING, TINTER:
                break
        }
 
-       isConstString = Isconst(nr, CTSTR)
+       isConstString := Isconst(nr, CTSTR)
        nodl = *nl
        if !cadable(nl) {
                if nr != nil && !cadable(nr) && !isConstString {
-                       goto no
+                       return false
                }
                Igen(nl, &nodl, nil)
-               freel = 1
+               defer Regfree(&nodl)
        }
 
        if nr != nil {
                nodr = *nr
                if !cadable(nr) && !isConstString {
                        Igen(nr, &nodr, nil)
-                       freer = 1
+                       defer Regfree(&nodr)
                }
        } else {
                // When zeroing, prepare a register containing zero.
@@ -1198,7 +1188,7 @@ func Componentgen(nr *Node, nl *Node) bool {
 
                Regalloc(&nodr, Types[TUINT], nil)
                Thearch.Gmove(&tmp, &nodr)
-               freer = 1
+               defer Regfree(&nodr)
        }
 
        // nl and nr are 'cadable' which basically means they are names (variables) now.
@@ -1206,12 +1196,15 @@ func Componentgen(nr *Node, nl *Node) bool {
        // VARDEF we generate will mark the old value as dead incorrectly.
        // (And also the assignments are useless.)
        if nr != nil && nl.Op == ONAME && nr.Op == ONAME && nl == nr {
-               goto yes
+               return true
        }
 
        switch nl.Type.Etype {
-       // componentgen for arrays.
+       default:
+               return false
+
        case TARRAY:
+               // componentgen for arrays.
                if nl.Op == ONAME {
                        Gvardef(nl)
                }
@@ -1228,8 +1221,7 @@ func Componentgen(nr *Node, nl *Node) bool {
                                nodl.Xoffset += t.Type.Width
                                nodr.Xoffset += t.Type.Width
                        }
-
-                       goto yes
+                       return true
                }
 
                // componentgen for slices.
@@ -1263,8 +1255,7 @@ func Componentgen(nr *Node, nl *Node) bool {
                }
 
                Thearch.Gmove(&nodr, &nodl)
-
-               goto yes
+               return true
 
        case TSTRING:
                if nl.Op == ONAME {
@@ -1297,8 +1288,7 @@ func Componentgen(nr *Node, nl *Node) bool {
                }
 
                Thearch.Gmove(&nodr, &nodl)
-
-               goto yes
+               return true
 
        case TINTER:
                if nl.Op == ONAME {
@@ -1323,8 +1313,7 @@ func Componentgen(nr *Node, nl *Node) bool {
                }
 
                Thearch.Gmove(&nodr, &nodl)
-
-               goto yes
+               return true
 
        case TSTRUCT:
                if nl.Op == ONAME {
@@ -1353,27 +1342,8 @@ func Componentgen(nr *Node, nl *Node) bool {
                                Thearch.Gmove(&nodr, &nodl)
                        }
                }
-
-               goto yes
-       }
-
-no:
-       if freer != 0 {
-               Regfree(&nodr)
-       }
-       if freel != 0 {
-               Regfree(&nodl)
-       }
-       return false
-
-yes:
-       if freer != 0 {
-               Regfree(&nodr)
-       }
-       if freel != 0 {
-               Regfree(&nodl)
+               return true
        }
-       return true
 }
 
 func cadable(n *Node) bool {