[dev.ssa] cmd/compile: implement genValue for MOVQstoreidx8

Change-Id: I6b13a26e01ef8739ed60e6fd5f5c1ea045bea581
Reviewed-on: https://go-review.googlesource.com/12793Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -1749,6 +1749,15 @@ func genValue(v *ssa.Value) {
 		p.To.Type = obj.TYPE_MEM
 		p.To.Reg = regnum(v.Args[0])
 		addAux(&p.To, v)
+	case ssa.OpAMD64MOVQstoreidx8:
+		p := Prog(x86.AMOVQ)
+		p.From.Type = obj.TYPE_REG
+		p.From.Reg = regnum(v.Args[2])
+		p.To.Type = obj.TYPE_MEM
+		p.To.Reg = regnum(v.Args[0])
+		p.To.Scale = 8
+		p.To.Index = regnum(v.Args[1])
+		addAux(&p.To, v)
 	case ssa.OpAMD64MOVLQSX, ssa.OpAMD64MOVWQSX, ssa.OpAMD64MOVBQSX, ssa.OpAMD64MOVLQZX, ssa.OpAMD64MOVWQZX, ssa.OpAMD64MOVBQZX:
 		p := Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG

src/cmd/compile/internal/ssa/gen/AMD64Ops.go

@@ -156,7 +156,7 @@ func init() {
 		{name: "MOVWstore", reg: gpstore, asm: "MOVW"},        // store 2 bytes in arg1 to arg0+auxint. arg2=mem
 		{name: "MOVLstore", reg: gpstore, asm: "MOVL"},        // store 4 bytes in arg1 to arg0+auxint. arg2=mem
 		{name: "MOVQstore", reg: gpstore, asm: "MOVQ"},        // store 8 bytes in arg1 to arg0+auxint. arg2=mem
-		{name: "MOVQstoreidx8", reg: gpstoreidx},            // store 8 bytes in arg2 to arg0+8*arg1+auxint. arg3=mem
+		{name: "MOVQstoreidx8", reg: gpstoreidx, asm: "MOVQ"}, // store 8 bytes in arg2 to arg0+8*arg1+auxint. arg3=mem
 
 		{name: "MOVXzero", reg: gpstoreconst}, // store auxint 0 bytes into arg0 using a series of MOV instructions. arg1=mem.
 		// TODO: implement this when register clobbering works

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

@@ -890,6 +890,7 @@ var opcodeTable = [...]opInfo{
 	},
 	{
 		name: "MOVQstoreidx8",
+		asm:  x86.AMOVQ,
 		reg: regInfo{
 			inputs: []regMask{
 				4295032831, // .AX .CX .DX .BX .SP .BP .SI .DI .R8 .R9 .R10 .R11 .R12 .R13 .R14 .R15 .SB