cmd/internal/obj/s390x: add FIDBR and FIEBR instructions

FIDBR and FIEBR can be used for floating-point to integer rounding.
The relevant functions (Ceil, Floor and Trunc) will be updated
in a future CL.

Change-Id: I5952d67ab29d5ef8923ff1143e17a8d30169d692
Reviewed-on: https://go-review.googlesource.com/27826Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -178,6 +178,8 @@ TEXT main·foo(SB),7,$16-0 // TEXT main.foo(SB), 7, $16-0
 	FABS	F1, F2                 // b3100021
 	FSQRTS	F3, F4                 // b3140043
 	FSQRT	F5, F15                // b31500f5
+	FIEBR	$0, F0, F1             // b3570010
+	FIDBR	$7, F2, F3             // b35f7032
 
 	VL	(R15), V1              // e710f0000006
 	VST	V1, (R15)              // e710f000000e

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

@@ -286,6 +286,8 @@ const (
 	AFSUBS
 	AFSQRT
 	AFSQRTS
+	AFIEBR
+	AFIDBR
 
 	// convert from int32/int64 to float/float64
 	ACEFBRA

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

@@ -79,6 +79,8 @@ var Anames = []string{
 	"FSUBS",
 	"FSQRT",
 	"FSQRTS",
+	"FIEBR",
+	"FIDBR",
 	"CEFBRA",
 	"CDFBRA",
 	"CEGBRA",

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

@@ -191,6 +191,7 @@ var optab = []Optab{
 	Optab{AFMOVD, C_ZCON, C_NONE, C_NONE, C_FREG, 67, 0},
 	Optab{ACEFBRA, C_REG, C_NONE, C_NONE, C_FREG, 82, 0},
 	Optab{ACFEBRA, C_FREG, C_NONE, C_NONE, C_REG, 83, 0},
+	Optab{AFIEBR, C_SCON, C_FREG, C_NONE, C_FREG, 48, 0},
 
 	// load symbol address (plus offset)
 	Optab{AMOVD, C_SYMADDR, C_NONE, C_NONE, C_REG, 19, 0},
@@ -912,6 +913,8 @@ func buildop(ctxt *obj.Link) {
 			opset(ACLFDBR, r)
 			opset(ACLGEBR, r)
 			opset(ACLGDBR, r)
+		case AFIEBR:
+			opset(AFIDBR, r)
 		case ACMPBEQ:
 			opset(ACMPBGE, r)
 			opset(ACMPBGT, r)
@@ -3205,6 +3208,20 @@ func asmout(ctxt *obj.Link, asm *[]byte) {
 			zRRE(op_LCGR, uint32(p.To.Reg), uint32(r), asm)
 		}
 
+	case 48: // floating-point round to integer
+		m3 := vregoff(ctxt, &p.From)
+		if 0 > m3 || m3 > 7 {
+			ctxt.Diag("mask (%v) must be in the range [0, 7]", m3)
+		}
+		var opcode uint32
+		switch p.As {
+		case AFIEBR:
+			opcode = op_FIEBR
+		case AFIDBR:
+			opcode = op_FIDBR
+		}
+		zRRF(opcode, uint32(m3), 0, uint32(p.To.Reg), uint32(p.Reg), asm)
+
 	case 67: // fmov $0 freg
 		var opcode uint32
 		switch p.As {