cmd/internal/obj: more Optab range simplification

Same idea as golang.org/cl/20322.

Passes toolstash/buildall.

Change-Id: Ida5960e57ff6e1e8de75c2720f21aeae56a8e415
Reviewed-on: https://go-review.googlesource.com/20352
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/obj/arm/asm5.go

@@ -50,11 +50,6 @@ type Optab struct {
 	pcrelsiz uint8
 }
 
-type Oprang struct {
-	start []Optab
-	stop  []Optab
-}
-
 type Opcross [32][2][32]uint8
 
 const (
@@ -270,9 +265,9 @@ var pool struct {
 	extra uint32
 }
 
-var oprange [ALAST & obj.AMask]Oprang
+var oprange [ALAST & obj.AMask][]Optab
 
-var xcmp [C_GOK + 1][C_GOK + 1]uint8
+var xcmp [C_GOK + 1][C_GOK + 1]bool
 
 var deferreturn *obj.LSym
 
@@ -563,7 +558,7 @@ func span5(ctxt *obj.Link, cursym *obj.LSym) {
 		return
 	}
 
-	if oprange[AAND&obj.AMask].start == nil {
+	if oprange[AAND&obj.AMask] == nil {
 		buildop(ctxt)
 	}
 
@@ -1174,7 +1169,7 @@ func prasm(p *obj.Prog) {
 func oplook(ctxt *obj.Link, p *obj.Prog) *Optab {
 	a1 := int(p.Optab)
 	if a1 != 0 {
-		return &optab[a1-1:][0]
+		return &optab[a1-1]
 	}
 	a1 = int(p.From.Class)
 	if a1 == 0 {
@@ -1194,38 +1189,30 @@ func oplook(ctxt *obj.Link, p *obj.Prog) *Optab {
 	if p.Reg != 0 {
 		a2 = C_REG
 	}
-	r := p.As & obj.AMask
-	o := oprange[r].start
-	if o == nil {
-		o = oprange[r].stop /* just generate an error */
-	}
 
 	if false { /*debug['O']*/
 		fmt.Printf("oplook %v %v %v %v\n", obj.Aconv(p.As), DRconv(a1), DRconv(a2), DRconv(a3))
 		fmt.Printf("\t\t%d %d\n", p.From.Type, p.To.Type)
 	}
 
-	e := oprange[r].stop
-	c1 := xcmp[a1][:]
-	c3 := xcmp[a3][:]
-	for ; -cap(o) < -cap(e); o = o[1:] {
-		if int(o[0].a2) == a2 {
-			if c1[o[0].a1] != 0 {
-				if c3[o[0].a3] != 0 {
-					p.Optab = uint16((-cap(o) + cap(optab)) + 1)
-					return &o[0]
-				}
-			}
+	ops := oprange[p.As&obj.AMask]
+	c1 := &xcmp[a1]
+	c3 := &xcmp[a3]
+	for i := range ops {
+		op := &ops[i]
+		if int(op.a2) == a2 && c1[op.a1] && c3[op.a3] {
+			p.Optab = uint16(cap(optab) - cap(ops) + i + 1)
+			return op
 		}
 	}
 
 	ctxt.Diag("illegal combination %v; %v %v %v, %d %d", p, DRconv(a1), DRconv(a2), DRconv(a3), p.From.Type, p.To.Type)
 	ctxt.Diag("from %d %d to %d %d\n", p.From.Type, p.From.Name, p.To.Type, p.To.Name)
 	prasm(p)
-	if o == nil {
-		o = optab
+	if ops == nil {
+		ops = optab
 	}
-	return &o[0]
+	return &ops[0]
 }
 
 func cmp(a int, b int) bool {
@@ -1329,7 +1316,7 @@ func buildop(ctxt *obj.Link) {
 	for i := 0; i < C_GOK; i++ {
 		for n = 0; n < C_GOK; n++ {
 			if cmp(n, i) {
-				xcmp[i][n] = 1
+				xcmp[i][n] = true
 			}
 		}
 	}
@@ -1347,11 +1334,11 @@ func buildop(ctxt *obj.Link) {
 	for i := 0; i < n; i++ {
 		r := optab[i].as
 		r0 := r & obj.AMask
-		oprange[r0].start = optab[i:]
+		start := i
 		for optab[i].as == r {
 			i++
 		}
-		oprange[r0].stop = optab[i:]
+		oprange[r0] = optab[start:i]
 		i--
 
 		switch r {

src/cmd/internal/obj/mips/asm0.go

@@ -310,14 +310,9 @@ var optab = []Optab{
 	{obj.AXXX, C_NONE, C_NONE, C_NONE, 0, 4, 0},
 }
 
-type Oprang struct {
-	start []Optab
-	stop  []Optab
-}
-
-var oprange [ALAST & obj.AMask]Oprang
+var oprange [ALAST & obj.AMask][]Optab
 
-var xcmp [C_NCLASS][C_NCLASS]uint8
+var xcmp [C_NCLASS][C_NCLASS]bool
 
 func span0(ctxt *obj.Link, cursym *obj.LSym) {
 	p := cursym.Text
@@ -327,7 +322,7 @@ func span0(ctxt *obj.Link, cursym *obj.LSym) {
 	ctxt.Cursym = cursym
 	ctxt.Autosize = int32(p.To.Offset + 8)
 
-	if oprange[AOR&obj.AMask].start == nil {
+	if oprange[AOR&obj.AMask] == nil {
 		buildop(ctxt)
 	}
 
@@ -610,7 +605,7 @@ func prasm(p *obj.Prog) {
 }
 
 func oplook(ctxt *obj.Link, p *obj.Prog) *Optab {
-	if oprange[AOR&obj.AMask].start == nil {
+	if oprange[AOR&obj.AMask] == nil {
 		buildop(ctxt)
 	}
 
@@ -638,32 +633,24 @@ func oplook(ctxt *obj.Link, p *obj.Prog) *Optab {
 	}
 
 	//print("oplook %P %d %d %d\n", p, a1, a2, a3);
-	r0 := p.As & obj.AMask
 
-	o := oprange[r0].start
-	if o == nil {
-		o = oprange[r0].stop /* just generate an error */
-	}
-	e := oprange[r0].stop
-	c1 := xcmp[a1][:]
-	c3 := xcmp[a3][:]
-	for ; -cap(o) < -cap(e); o = o[1:] {
-		if int(o[0].a2) == a2 {
-			if c1[o[0].a1] != 0 {
-				if c3[o[0].a3] != 0 {
-					p.Optab = uint16((-cap(o) + cap(optab)) + 1)
-					return &o[0]
-				}
-			}
+	ops := oprange[p.As&obj.AMask]
+	c1 := &xcmp[a1]
+	c3 := &xcmp[a3]
+	for i := range ops {
+		op := &ops[i]
+		if int(op.a2) == a2 && c1[op.a1] && c3[op.a3] {
+			p.Optab = uint16(cap(optab) - cap(ops) + i + 1)
+			return op
 		}
 	}
 
 	ctxt.Diag("illegal combination %v %v %v %v", obj.Aconv(p.As), DRconv(a1), DRconv(a2), DRconv(a3))
 	prasm(p)
-	if o == nil {
-		o = optab
+	if ops == nil {
+		ops = optab
 	}
-	return &o[0]
+	return &ops[0]
 }
 
 func cmp(a int, b int) bool {
@@ -788,7 +775,7 @@ func buildop(ctxt *obj.Link) {
 	for i := 0; i < C_NCLASS; i++ {
 		for n = 0; n < C_NCLASS; n++ {
 			if cmp(n, i) {
-				xcmp[i][n] = 1
+				xcmp[i][n] = true
 			}
 		}
 	}
@@ -798,11 +785,11 @@ func buildop(ctxt *obj.Link) {
 	for i := 0; i < n; i++ {
 		r := optab[i].as
 		r0 := r & obj.AMask
-		oprange[r0].start = optab[i:]
+		start := i
 		for optab[i].as == r {
 			i++
 		}
-		oprange[r0].stop = optab[i:]
+		oprange[r0] = optab[start:i]
 		i--
 
 		switch r {