cmd/internal/obj/s390x: add VSTRL instruction

VSTRL (Vector Store Righmost with Length) instruction
is used to store specified number of rightmost bytes of
a Vector register into a memory location.

This change will add VSTRL into the Go asm for s390x architecture.
An upcoming PR of bigmod/nat_s390x.s will use this
instruction for performance improvement.

Change-Id: I18b5b55025930fda78adb466cc0f26238f73dd6e
Reviewed-on: https://go-review.googlesource.com/c/go/+/755520
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Srinivas Pokala <Pokala.Srinivas@ibm.com>

src/cmd/asm/internal/asm/testdata/s390x.s

@@ -456,6 +456,7 @@ TEXT main·foo(SB),DUPOK|NOSPLIT,$16-0 // TEXT main.foo(SB), DUPOK|NOSPLIT, $16-
 	VST	V1, (R15)               // e710f000000e
 	VL	(R15), V31              // e7f0f0000806
 	VST	V31, (R15)              // e7f0f000080e
+	VSTRL	V4, $6, 1(R4)           // e6064001403d
 	VESLB	$5, V14                 // e7ee00050030
 	VESRAG	$0, V15, V16            // e70f0000383a
 	VLM	(R15), V8, V23          // e787f0000436

src/cmd/internal/obj/s390x/a.out.go

@@ -946,6 +946,7 @@ const (
 	AVSTEG
 	AVSTEB
 	AVSTM
+	AVSTRL
 	AVSTL
 	AVSTRC
 	AVSTRCB

src/cmd/internal/obj/s390x/anames.go

@@ -669,6 +669,7 @@ var Anames = []string{
 	"VSTEG",
 	"VSTEB",
 	"VSTM",
+	"VSTRL",
 	"VSTL",
 	"VSTRC",
 	"VSTRCB",

src/cmd/internal/obj/s390x/asmz.go

@@ -458,6 +458,10 @@ var optab = []Optab{
 	// MVC storage and storage
 	{i: 127, as: AMVCLE, a1: C_LOREG, a2: C_REG, a6: C_REG},
 	{i: 127, as: AMVCLE, a1: C_SCON, a2: C_REG, a6: C_REG},
+
+	// VSI store rightmost with length
+	{i: 129, as: AVSTRL, a1: C_VREG, a3: C_SCON, a6: C_SOREG},
+	{i: 129, as: AVSTRL, a1: C_VREG, a3: C_SCON, a6: C_SAUTO},
 }
 
 var oprange [ALAST & obj.AMask][]Optab
@@ -2634,6 +2638,7 @@ const (
 	op_VSTEG  uint32 = 0xE70A // 	VRX	VECTOR STORE ELEMENT (64)
 	op_VSTEB  uint32 = 0xE708 // 	VRX	VECTOR STORE ELEMENT (8)
 	op_VSTM   uint32 = 0xE73E // 	VRS-a	VECTOR STORE MULTIPLE
+	op_VSTRL  uint32 = 0xE63D // 	VSI	VECTOR STORE RIGHTMOST WITH LENGTH
 	op_VSTL   uint32 = 0xE73F // 	VRS-b	VECTOR STORE WITH LENGTH
 	op_VSTRC  uint32 = 0xE78A // 	VRR-d	VECTOR STRING RANGE COMPARE
 	op_VS     uint32 = 0xE7F7 // 	VRR-c	VECTOR SUBTRACT
@@ -4459,7 +4464,7 @@ func (c *ctxtz) asmout(p *obj.Prog, asm *[]byte) {
 		}
 		zRRF(opcode, uint32(p.Reg), 0, uint32(p.From.Reg), uint32(p.To.Reg), asm)
 
-	case 127:
+	case 127: // RS-a Move Long Extended
 		// NOTE: Mapping MVCLE operands is as follows:
 		// Instruction Format: MVCLE R1,R3,D2(B2)
 		// R1 - prog.To (for Destination)
@@ -4482,6 +4487,17 @@ func (c *ctxtz) asmout(p *obj.Prog, asm *[]byte) {
 		m5 := singleElementMask(p.As)
 		m6 := uint32(c.vregoff(&p.From))
 		zVRRc(op, uint32(p.To.Reg), uint32(p.Reg), uint32(p.GetFrom3().Reg), m6, m5, m4, asm)
+
+	case 129: // VSI Vector Store Rightmost with Length
+		op, _, _ := vop(p.As)
+		v1 := p.From.Reg
+		b2 := p.To.Reg
+		if b2 == 0 {
+			b2 = REGSP
+		}
+		d2 := uint32(c.vregoff(&p.To))
+		i3 := uint32(c.vregoff(p.GetFrom3()))
+		zVSI(op, uint32(v1), uint32(b2), d2, i3, asm)
 	}
 }
 
@@ -5081,3 +5097,13 @@ func zVRIe(op, v1, v2, i3, m5, m4 uint32, asm *[]byte) {
 		(uint8(m4)<<4)|rxb(v1, v2, 0, 0),
 		uint8(op))
 }
+
+func zVSI(op, v1, b2, d2, i3 uint32, asm *[]byte) {
+	*asm = append(*asm,
+		uint8(op>>8),
+		uint8(i3),
+		(uint8(b2)<<4)|(uint8(d2>>8)&0xf),
+		uint8(d2),
+		(uint8(v1)<<4)|rxb(v1, 0, 0, 0),
+		uint8(op))
+}

src/cmd/internal/obj/s390x/vector.go

@@ -915,6 +915,8 @@ func vop(as obj.As) (opcode, es, cs uint32) {
 		return op_VSTEB, 0, 0
 	case AVSTM:
 		return op_VSTM, 0, 0
+	case AVSTRL:
+		return op_VSTRL, 0, 0
 	case AVSTL:
 		return op_VSTL, 0, 0
 	case AVSTRC: