cmd/asm: add 'insert program mask' instruction for s390x

This CL adds the 'insert program mask' (IPM) instruction to s390x.
IPM stores the current program mask (which contains the condition
code) into a general purpose register.

This instruction will be useful when implementing intrinsics for
the arithmetic functions in the math/bits package. We can also
potentially use it to convert some condition codes into bool
values.

The condition code can be saved and restored using an instruction
sequence such as:

  IPM  R4          // save condition code to R4
  ...
  TMLH R4, $0x3000 // restore condition code from R4

We can also use IPM to save the carry bit to a register using an
instruction sequence such as:

  IPM     R4                   // save condition code to R4
  RISBLGZ $31, $31, $3, R4, R4 // isolate carry bit in R4

Change-Id: I169d450b6ea1a7ff8c0286115ddc42618da8a2f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/165997
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -219,6 +219,9 @@ TEXT main·foo(SB),DUPOK|NOSPLIT,$16-0 // TEXT main.foo(SB), DUPOK|NOSPLIT, $16-
 	TMLH	R3, $0                 // a7300000
 	TMLL	R4, $32768             // a7418000
 
+	IPM	R3                     // b2220030
+	IPM	R12                    // b22200c0
+
 	BNE	0(PC)                  // a7740000
 	BEQ	0(PC)                  // a7840000
 	BLT	0(PC)                  // a7440000

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

@@ -366,6 +366,9 @@ const (
 	ATMLH
 	ATMLL
 
+	// insert program mask
+	AIPM
+
 	// compare and swap
 	ACS
 	ACSG

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

@@ -120,6 +120,7 @@ var Anames = []string{
 	"TMHL",
 	"TMLH",
 	"TMLL",
+	"IPM",
 	"CS",
 	"CSG",
 	"SYNC",

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

@@ -260,6 +260,9 @@ var optab = []Optab{
 	// test under mask
 	Optab{ATMHH, C_REG, C_NONE, C_NONE, C_ANDCON, 91, 0},
 
+	// insert program mask
+	Optab{AIPM, C_REG, C_NONE, C_NONE, C_NONE, 92, 0},
+
 	// 32-bit access registers
 	Optab{AMOVW, C_AREG, C_NONE, C_NONE, C_REG, 68, 0},
 	Optab{AMOVWZ, C_AREG, C_NONE, C_NONE, C_REG, 68, 0},
@@ -3766,6 +3769,9 @@ func (c *ctxtz) asmout(p *obj.Prog, asm *[]byte) {
 		}
 		zRI(opcode, uint32(p.From.Reg), uint32(c.vregoff(&p.To)), asm)
 
+	case 92: // insert program mask
+		zRRE(op_IPM, uint32(p.From.Reg), 0, asm)
+
 	case 93: // GOT lookup
 		v := c.vregoff(&p.To)
 		if v != 0 {