cmd/compile: enable rewritings that are blocked by old backends

Old backends did not implement them, but SSA do.

Change-Id: I543b2281dcf4bab0da37c9b1f26a5ef55a0ea11b
Reviewed-on: https://go-review.googlesource.com/29278
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/walk.go

@@ -3387,8 +3387,7 @@ func samecheap(a *Node, b *Node) bool {
 // The result of walkrotate MUST be assigned back to n, e.g.
 // 	n.Left = walkrotate(n.Left)
 func walkrotate(n *Node) *Node {
-	//TODO: enable LROT on ARM64 once the old backend is gone
-	if Thearch.LinkArch.InFamily(sys.MIPS64, sys.ARM64, sys.PPC64) {
+	if Thearch.LinkArch.InFamily(sys.MIPS64, sys.PPC64) {
 		return n
 	}
 
@@ -3647,11 +3646,6 @@ ret:
 func walkdiv(n *Node, init *Nodes) *Node {
 	// if >= 0, nr is 1<<pow // 1 if nr is negative.
 
-	// TODO(minux)
-	if Thearch.LinkArch.InFamily(sys.MIPS64, sys.PPC64) {
-		return n
-	}
-
 	if n.Right.Op != OLITERAL {
 		return n
 	}

src/cmd/compile/internal/ppc64/prog.go

@@ -54,8 +54,10 @@ var progtable = [ppc64.ALAST & obj.AMask]obj.ProgInfo{
 	ppc64.AEQV & obj.AMask:    {Flags: gc.SizeQ | gc.LeftRead | gc.RegRead | gc.RightWrite},
 	ppc64.AMULLD & obj.AMask:  {Flags: gc.SizeQ | gc.LeftRead | gc.RegRead | gc.RightWrite},
 	ppc64.AMULLW & obj.AMask:  {Flags: gc.SizeL | gc.LeftRead | gc.RegRead | gc.RightWrite},
-	ppc64.AMULHD & obj.AMask:  {Flags: gc.SizeL | gc.LeftRead | gc.RegRead | gc.RightWrite},
-	ppc64.AMULHDU & obj.AMask: {Flags: gc.SizeL | gc.LeftRead | gc.RegRead | gc.RightWrite},
+	ppc64.AMULHD & obj.AMask:  {Flags: gc.SizeQ | gc.LeftRead | gc.RegRead | gc.RightWrite},
+	ppc64.AMULHDU & obj.AMask: {Flags: gc.SizeQ | gc.LeftRead | gc.RegRead | gc.RightWrite},
+	ppc64.AMULHW & obj.AMask:  {Flags: gc.SizeL | gc.LeftRead | gc.RegRead | gc.RightWrite},
+	ppc64.AMULHWU & obj.AMask: {Flags: gc.SizeL | gc.LeftRead | gc.RegRead | gc.RightWrite},
 	ppc64.ADIVD & obj.AMask:   {Flags: gc.SizeQ | gc.LeftRead | gc.RegRead | gc.RightWrite},
 	ppc64.ADIVDU & obj.AMask:  {Flags: gc.SizeQ | gc.LeftRead | gc.RegRead | gc.RightWrite},
 	ppc64.ADIVW & obj.AMask:   {Flags: gc.SizeL | gc.LeftRead | gc.RegRead | gc.RightWrite},