cmd/7g: change CHECKNIL sequence

We can use CBNZ instruction and make it one instruction shorter.

Saves 66kB in godoc.

Change-Id: Ie71fe7cf31e7f73644ee926f4f9624c009c3eb1a
Reviewed-on: https://go-review.googlesource.com/8634
Reviewed-by: Minux Ma <minux@golang.org>

diff --git a/src/cmd/7g/ggen.go b/src/cmd/7g/ggen.go
index c8f65a68d1558c4106b0048acf5481236173460b..9b3ffce38af4280d18d68deb611d1d94bbbe9caf 100644 (file)
--- a/src/cmd/7g/ggen.go
+++ b/src/cmd/7g/ggen.go
@@ -483,7 +483,6 @@ func clearfat(nl *gc.Node) {
 // Expand CHECKNIL pseudo-op into actual nil pointer check.
 func expandchecks(firstp *obj.Prog) {
        var p1 *obj.Prog
-       var p2 *obj.Prog
 
        for p := (*obj.Prog)(firstp); p != nil; p = p.Link {
                if gc.Debug_checknil != 0 && gc.Ctxt.Debugvlog != 0 {
@@ -500,38 +499,26 @@ func expandchecks(firstp *obj.Prog) {
                }
 
                // check is
-               //      CMP arg, ZR
-               //      BNE 2(PC) [likely]
+               //      CBNZ arg, 2(PC)
                //      MOVD ZR, 0(arg)
                p1 = gc.Ctxt.NewProg()
-
-               p2 = gc.Ctxt.NewProg()
                gc.Clearp(p1)
-               gc.Clearp(p2)
-               p1.Link = p2
-               p2.Link = p.Link
+               p1.Link = p.Link
                p.Link = p1
                p1.Lineno = p.Lineno
-               p2.Lineno = p.Lineno
                p1.Pc = 9999
-               p2.Pc = 9999
-               p.As = arm64.ACMP
-               p.Reg = arm64.REGZERO
-               p1.As = arm64.ABNE
-
-               //p1->from.type = TYPE_CONST;
-               //p1->from.offset = 1; // likely
-               p1.To.Type = obj.TYPE_BRANCH
 
-               p1.To.Val = p2.Link
+               p.As = arm64.ACBNZ
+               p.To.Type = obj.TYPE_BRANCH
+               p.To.Val = p1.Link
 
                // crash by write to memory address 0.
-               p2.As = arm64.AMOVD
-               p2.From.Type = obj.TYPE_REG
-               p2.From.Reg = arm64.REGZERO
-               p2.To.Type = obj.TYPE_MEM
-               p2.To.Reg = p.From.Reg
-               p2.To.Offset = 0
+               p1.As = arm64.AMOVD
+               p1.From.Type = obj.TYPE_REG
+               p1.From.Reg = arm64.REGZERO
+               p1.To.Type = obj.TYPE_MEM
+               p1.To.Reg = p.From.Reg
+               p1.To.Offset = 0
        }
 }
 

diff --git a/src/cmd/7g/prog.go b/src/cmd/7g/prog.go
index 733c405fac77066b71a2d65f17930f97ca1d42ce..023f302e14adf4cf544f76fd9b12fd6ffb5611ba 100644 (file)
--- a/src/cmd/7g/prog.go
+++ b/src/cmd/7g/prog.go
@@ -122,6 +122,8 @@ var progtable = [arm64.ALAST]obj.ProgInfo{
        arm64.ABLS:    {gc.Cjmp, 0, 0, 0},
        arm64.ABHI:    {gc.Cjmp, 0, 0, 0},
        arm64.ABHS:    {gc.Cjmp, 0, 0, 0},
+       arm64.ACBZ:    {gc.Cjmp, 0, 0, 0},
+       arm64.ACBNZ:   {gc.Cjmp, 0, 0, 0},
        obj.ARET:      {gc.Break, 0, 0, 0},
        obj.ADUFFZERO: {gc.Call, 0, 0, 0},
        obj.ADUFFCOPY: {gc.Call, 0, 0, 0},