cmd/compile: allow 64-bit multiplication with immediates on s390x

MGHI (16-bit signed immediate) is now used where possible for both
MULLW and MULLD. MGHI is 2-bytes shorter than MSGFI.

Change-Id: I5d0648934f28b3403b1126913fd703d8f62b9e9f
Reviewed-on: https://go-review.googlesource.com/22398
Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bill O'Farrell <billotosyr@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -59,8 +59,12 @@ TEXT main·foo(SB),7,$16-0 // TEXT main.foo(SB), 7, $16-0
 	SUBC	R2, R3, R4            // b9eb2043
 	MULLW	R6, R7                // b91c0076
 	MULLW	R6, R7, R8            // b9040087b91c0086
-	MULLW	$8192, R6             // c26000002000
-	MULLW	$8192, R6, R7         // b9040076c27000002000
+	MULLW	$8192, R6             // a76d2000
+	MULLW	$8192, R6, R7         // b9040076a77d2000
+	MULLW	$-65537, R8           // c280fffeffff
+	MULLW   $-65537, R8, R9       // b9040098c290fffeffff
+	MULLD	$-2147483648, R1      // c21080000000
+	MULLD   $-2147483648, R1, R2  // b9040021c22080000000
 	MULHD	R9, R8                // b90400b8b98600a9ebb9003f000ab98000b8b90900abebb8003f000ab98000b9b9e9b08a
 	MULHD	R7, R2, R1            // b90400b2b98600a7ebb7003f000ab98000b2b90900abebb2003f000ab98000b7b9e9b01a
 	MULHDU	R3, R4                // b90400b4b98600a3b904004a

src/cmd/compile/internal/s390x/gsubr.go

@@ -54,7 +54,7 @@ func ginscon(as obj.As, c int64, n2 *gc.Node) {
 
 	gc.Nodconst(&n1, gc.Types[gc.TINT64], c)
 
-	if as != s390x.AMOVD && (c < -s390x.BIG || c > s390x.BIG) || n2.Op != gc.OREGISTER || as == s390x.AMULLD {
+	if as != s390x.AMOVD && (c < -s390x.BIG || c > s390x.BIG) || n2.Op != gc.OREGISTER {
 		// cannot have more than 16-bit of immediate in ADD, etc.
 		// instead, MOV into register first.
 		var ntmp gc.Node
@@ -562,11 +562,6 @@ func rawgins(as obj.As, f *gc.Node, t *gc.Node) *obj.Prog {
 
 	switch as {
 	// Bad things the front end has done to us. Crash to find call stack.
-	case s390x.AMULLD:
-		if p.From.Type == obj.TYPE_CONST {
-			gc.Debug['h'] = 1
-			gc.Fatalf("bad inst: %v", p)
-		}
 	case s390x.ACMP, s390x.ACMPU:
 		if p.From.Type == obj.TYPE_MEM || p.To.Type == obj.TYPE_MEM {
 			gc.Debug['h'] = 1

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

@@ -142,14 +142,6 @@ var optab = []Optab{
 	Optab{AADD, C_REG, C_NONE, C_NONE, C_REG, 2, 0},
 	Optab{AADD, C_LCON, C_REG, C_NONE, C_REG, 22, 0},
 	Optab{AADD, C_LCON, C_NONE, C_NONE, C_REG, 22, 0},
-	Optab{AADDC, C_REG, C_REG, C_NONE, C_REG, 2, 0},
-	Optab{AADDC, C_REG, C_NONE, C_NONE, C_REG, 2, 0},
-	Optab{AADDC, C_LCON, C_REG, C_NONE, C_REG, 22, 0},
-	Optab{AADDC, C_LCON, C_NONE, C_NONE, C_REG, 22, 0},
-	Optab{AMULLW, C_REG, C_REG, C_NONE, C_REG, 2, 0},
-	Optab{AMULLW, C_REG, C_NONE, C_NONE, C_REG, 2, 0},
-	Optab{AMULLW, C_LCON, C_REG, C_NONE, C_REG, 22, 0},
-	Optab{AMULLW, C_LCON, C_NONE, C_NONE, C_REG, 22, 0},
 	Optab{AMULHD, C_REG, C_NONE, C_NONE, C_REG, 4, 0},
 	Optab{AMULHD, C_REG, C_REG, C_NONE, C_REG, 4, 0},
 	Optab{ASUBC, C_REG, C_REG, C_NONE, C_REG, 10, 0},
@@ -792,9 +784,12 @@ func buildop(ctxt *obj.Link) {
 		// opset() aliases optab ranges for similar instructions, to reduce the number of optabs in the array.
 		// oprange[] is used by oplook() to find the Optab entry that applies to a given Prog.
 		switch r {
+		case AADD:
+			opset(AADDC, r)
+			opset(AMULLD, r)
+			opset(AMULLW, r)
 		case ADIVW:
 			opset(AADDE, r)
-			opset(AMULLD, r)
 			opset(ADIVD, r)
 			opset(ADIVDU, r)
 			opset(ADIVWU, r)
@@ -2935,12 +2930,16 @@ func asmout(ctxt *obj.Link, asm *[]byte) {
 				zRRE(op_LGR, uint32(p.To.Reg), uint32(r), asm)
 			}
 			zRIL(_a, op_ALGFI, uint32(p.To.Reg), uint32(v), asm)
-		case AMULLW:
+		case AMULLW, AMULLD:
 			if r != p.To.Reg {
 				zRRE(op_LGR, uint32(p.To.Reg), uint32(r), asm)
 			}
+			if int64(int16(v)) == v {
+				zRI(op_MGHI, uint32(p.To.Reg), uint32(v), asm)
+			} else {
 				zRIL(_a, op_MSGFI, uint32(p.To.Reg), uint32(v), asm)
 			}
+		}
 
 	case 23: // logical op $constant [reg] reg
 		v := vregoff(ctxt, &p.From)