cmd/compile: make more use of value switches

Use them to replace if/else chains with at least three comparisons,
where the code becomes clearly simpler.

Passes toolstash -cmp on std cmd.

Change-Id: Ic98aa3905944ddcab5aef5f9d9ba376853263d94
Reviewed-on: https://go-review.googlesource.com/70934
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/esc.go

@@ -129,7 +129,8 @@ func (v *bottomUpVisitor) visitcode(n *Node, min uint32) uint32 {
 	min = v.visitcodelist(n.Nbody, min)
 	min = v.visitcodelist(n.Rlist, min)
 
-	if n.Op == OCALLFUNC || n.Op == OCALLMETH {
+	switch n.Op {
+	case OCALLFUNC, OCALLMETH:
 		fn := n.Left
 		if n.Op == OCALLMETH {
 			fn = asNode(n.Left.Sym.Def)
@@ -140,9 +141,8 @@ func (v *bottomUpVisitor) visitcode(n *Node, min uint32) uint32 {
 				min = m
 			}
 		}
-	}
 
-	if n.Op == OCLOSURE {
+	case OCLOSURE:
 		m := v.visit(n.Func.Closure)
 		if m < min {
 			min = m
@@ -1279,16 +1279,14 @@ func parsetag(note string) uint16 {
 // to the second output (and if there are more than two outputs, there is no flow to those.)
 func describeEscape(em uint16) string {
 	var s string
-	if em&EscMask == EscUnknown {
+	switch em & EscMask {
+	case EscUnknown:
 		s = "EscUnknown"
-	}
+	case EscNone:
-	if em&EscMask == EscNone {
 		s = "EscNone"
-	}
+	case EscHeap:
-	if em&EscMask == EscHeap {
 		s = "EscHeap"
-	}
+	case EscReturn:
-	if em&EscMask == EscReturn {
 		s = "EscReturn"
 	}
 	if em&EscContentEscapes != 0 {

src/cmd/compile/internal/gc/noder.go

@@ -224,15 +224,14 @@ func (p *noder) importDecl(imp *syntax.ImportDecl) {
 	pack.Sym = my
 	pack.Name.Pkg = ipkg
 
-	if my.Name == "." {
+	switch my.Name {
+	case ".":
 		importdot(ipkg, pack)
 		return
-	}
+	case "init":
-	if my.Name == "init" {
 		yyerrorl(pack.Pos, "cannot import package as init - init must be a func")
 		return
-	}
+	case "_":
-	if my.Name == "_" {
 		return
 	}
 	if my.Def != nil {

src/cmd/compile/internal/gc/sinit.go

@@ -213,10 +213,10 @@ func init2(n *Node, out *[]*Node) {
 	init2list(n.Rlist, out)
 	init2list(n.Nbody, out)
 
-	if n.Op == OCLOSURE {
+	switch n.Op {
+	case OCLOSURE:
 		init2list(n.Func.Closure.Nbody, out)
-	}
+	case ODOTMETH, OCALLPART:
-	if n.Op == ODOTMETH || n.Op == OCALLPART {
 		init2(asNode(n.Type.FuncType().Nname), out)
 	}
 }

src/cmd/compile/internal/gc/ssa.go

@@ -2323,7 +2323,8 @@ func (s *state) append(n *Node, inplace bool) *ssa.Value {
 // This function is intended to handle && and || better than just calling
 // s.expr(cond) and branching on the result.
 func (s *state) condBranch(cond *Node, yes, no *ssa.Block, likely int8) {
-	if cond.Op == OANDAND {
+	switch cond.Op {
+	case OANDAND:
 		mid := s.f.NewBlock(ssa.BlockPlain)
 		s.stmtList(cond.Ninit)
 		s.condBranch(cond.Left, mid, no, max8(likely, 0))
@@ -2336,8 +2337,7 @@ func (s *state) condBranch(cond *Node, yes, no *ssa.Block, likely int8) {
 		// the likeliness of the first branch.
 		// TODO: have the frontend give us branch prediction hints for
 		// OANDAND and OOROR nodes (if it ever has such info).
-	}
+	case OOROR:
-	if cond.Op == OOROR {
 		mid := s.f.NewBlock(ssa.BlockPlain)
 		s.stmtList(cond.Ninit)
 		s.condBranch(cond.Left, yes, mid, min8(likely, 0))
@@ -2347,8 +2347,7 @@ func (s *state) condBranch(cond *Node, yes, no *ssa.Block, likely int8) {
 		// Note: if likely==-1, then both recursive calls pass -1.
 		// If likely==1, then we don't have enough info to decide
 		// the likelihood of the first branch.
-	}
+	case ONOT:
-	if cond.Op == ONOT {
 		s.stmtList(cond.Ninit)
 		s.condBranch(cond.Left, no, yes, -likely)
 		return
@@ -3990,14 +3989,15 @@ func (s *state) referenceTypeBuiltin(n *Node, x *ssa.Value) *ssa.Value {
 
 	b.AddEdgeTo(bElse)
 	s.startBlock(bElse)
-	if n.Op == OLEN {
+	switch n.Op {
+	case OLEN:
 		// length is stored in the first word for map/chan
 		s.vars[n] = s.newValue2(ssa.OpLoad, lenType, x, s.mem())
-	} else if n.Op == OCAP {
+	case OCAP:
 		// capacity is stored in the second word for chan
 		sw := s.newValue1I(ssa.OpOffPtr, lenType.PtrTo(), lenType.Width, x)
 		s.vars[n] = s.newValue2(ssa.OpLoad, lenType, sw, s.mem())
-	} else {
+	default:
 		s.Fatalf("op must be OLEN or OCAP")
 	}
 	s.endBlock()

src/cmd/compile/internal/gc/walk.go

@@ -990,61 +990,55 @@ opswitch:
 		n = walkexpr(n, init)
 
 	case OCONV, OCONVNOP:
-		if thearch.LinkArch.Family == sys.ARM || thearch.LinkArch.Family == sys.MIPS {
+		switch thearch.LinkArch.Family {
+		case sys.ARM, sys.MIPS:
 			if n.Left.Type.IsFloat() {
-				if n.Type.Etype == TINT64 {
+				switch n.Type.Etype {
+				case TINT64:
 					n = mkcall("float64toint64", n.Type, init, conv(n.Left, types.Types[TFLOAT64]))
-					break
+					break opswitch
-				}
+				case TUINT64:
-
-				if n.Type.Etype == TUINT64 {
 					n = mkcall("float64touint64", n.Type, init, conv(n.Left, types.Types[TFLOAT64]))
-					break
+					break opswitch
 				}
 			}
 
 			if n.Type.IsFloat() {
-				if n.Left.Type.Etype == TINT64 {
+				switch n.Left.Type.Etype {
+				case TINT64:
 					n = conv(mkcall("int64tofloat64", types.Types[TFLOAT64], init, conv(n.Left, types.Types[TINT64])), n.Type)
-					break
+					break opswitch
-				}
+				case TUINT64:
-
-				if n.Left.Type.Etype == TUINT64 {
 					n = conv(mkcall("uint64tofloat64", types.Types[TFLOAT64], init, conv(n.Left, types.Types[TUINT64])), n.Type)
-					break
+					break opswitch
 				}
 			}
-		}
 
-		if thearch.LinkArch.Family == sys.I386 {
+		case sys.I386:
 			if n.Left.Type.IsFloat() {
-				if n.Type.Etype == TINT64 {
+				switch n.Type.Etype {
+				case TINT64:
 					n = mkcall("float64toint64", n.Type, init, conv(n.Left, types.Types[TFLOAT64]))
-					break
+					break opswitch
-				}
+				case TUINT64:
-
-				if n.Type.Etype == TUINT64 {
 					n = mkcall("float64touint64", n.Type, init, conv(n.Left, types.Types[TFLOAT64]))
-					break
+					break opswitch
-				}
+				case TUINT32, TUINT, TUINTPTR:
-				if n.Type.Etype == TUINT32 || n.Type.Etype == TUINT || n.Type.Etype == TUINTPTR {
 					n = mkcall("float64touint32", n.Type, init, conv(n.Left, types.Types[TFLOAT64]))
-					break
+					break opswitch
 				}
 			}
 			if n.Type.IsFloat() {
-				if n.Left.Type.Etype == TINT64 {
+				switch n.Left.Type.Etype {
+				case TINT64:
 					n = conv(mkcall("int64tofloat64", types.Types[TFLOAT64], init, conv(n.Left, types.Types[TINT64])), n.Type)
-					break
+					break opswitch
-				}
+				case TUINT64:
-
-				if n.Left.Type.Etype == TUINT64 {
 					n = conv(mkcall("uint64tofloat64", types.Types[TFLOAT64], init, conv(n.Left, types.Types[TUINT64])), n.Type)
-					break
+					break opswitch
-				}
+				case TUINT32, TUINT, TUINTPTR:
-				if n.Left.Type.Etype == TUINT32 || n.Left.Type.Etype == TUINT || n.Left.Type.Etype == TUINTPTR {
 					n = conv(mkcall("uint32tofloat64", types.Types[TFLOAT64], init, conv(n.Left, types.Types[TUINT32])), n.Type)
-					break
+					break opswitch
 				}
 			}
 		}
@@ -2419,22 +2413,21 @@ func reorder3save(n *Node, all []*Node, i int, early *[]*Node) *Node {
 // outer value means containing struct or array.
 func outervalue(n *Node) *Node {
 	for {
-		if n.Op == OXDOT {
+		switch n.Op {
+		case OXDOT:
 			Fatalf("OXDOT in walk")
-		}
+		case ODOT, OPAREN, OCONVNOP:
-		if n.Op == ODOT || n.Op == OPAREN || n.Op == OCONVNOP {
-			n = n.Left
-			continue
-		}
-
-		if n.Op == OINDEX && n.Left.Type != nil && n.Left.Type.IsArray() {
 			n = n.Left
 			continue
+		case OINDEX:
+			if n.Left.Type != nil && n.Left.Type.IsArray() {
+				n = n.Left
+				continue
+			}
 		}
 
 		break
 	}
-
 	return n
 }