cmd/asm, cmd/internal/obj/s390x: fix encoding of VREPI{H,F,G}

Also adds tests for all missing VRI-a instructions (which may be
affected by this change).

Fixes #18749.

Change-Id: I48249dda626f32555da9ab58659e2e140de6504a
Reviewed-on: https://go-review.googlesource.com/35561
Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -294,6 +294,9 @@ TEXT main·foo(SB),7,$16-0 // TEXT main.foo(SB), 7, $16-0
 	VZERO	V16                    // e70000000844
 	VGBM	$52428, V31            // e7f0cccc0844
 	VREPIB	$255, V4               // e74000ff0045
+	VREPIH	$-1, V16               // e700ffff1845
+	VREPIF	$-32768, V0            // e70080002045
+	VREPIG	$32767, V31            // e7f07fff3845
 	VREPG	$1, V4, V16            // e7040001384d
 	VREPB	$4, V31, V1            // e71f0004044d
 	VFTCIDB	$4095, V1, V2          // e721fff0304a
@@ -318,7 +321,10 @@ TEXT main·foo(SB),7,$16-0 // TEXT main.foo(SB), 7, $16-0
 	VLL	R0, (R15), V1           // VLL     (R15), R0, V1           // e710f0000037
 	VSTL	R0, V16, (R15)          // VSTL    V16, R0, (R15)          // e700f000083f
 	VGMH	$8, $16, V12            // VGMH    $16, $8, V12            // e7c008101046
+	VLEIB	$15, $255, V0           // VLEIB   $255, $15, V0           // e70000fff040
+	VLEIH	$7, $-32768, V15        // VLEIH   $-32768, $7, V15        // e7f080007041
 	VLEIF	$2, $-43, V16           // VLEIF   $-43, $2, V16           // e700ffd52843
+	VLEIG	$1, $32767, V31         // VLEIG   $32767, $1, V31         // e7f07fff1842
 	VSLDB	$3, V1, V16, V18        // VSLDB   V1, V16, $3, V18        // e72100030a77
 	VERIMB	$2, V31, V1, V2         // VERIMB  V31, V1, $2, V2         // e72f10020472
 	VSEL	V1, V2, V3, V4          // VSEL    V2, V3, V1, V4          // e7412000308d

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

@@ -4014,7 +4014,7 @@ func asmout(ctxt *obj.Link, asm *[]byte) {
 		zVRS(op, uint32(p.To.Reg), uint32(p.From3.Reg), uint32(reg), offset, 0, asm)
 
 	case 109: // VRI-a
-		op, _, _ := vop(p.As)
+		op, m3, _ := vop(p.As)
 		i2 := uint32(vregoff(ctxt, &p.From))
 		switch p.As {
 		case AVZERO:
@@ -4022,7 +4022,6 @@ func asmout(ctxt *obj.Link, asm *[]byte) {
 		case AVONE:
 			i2 = 0xffff
 		}
-		m3 := uint32(0)
 		if p.From3 != nil {
 			m3 = uint32(vregoff(ctxt, p.From3))
 		}