cmd/compile: encapsulate OSLICE* representation
As a nice side-effect, this allows us to
unify several code paths.
The terminology (low, high, max, simple slice expr,
full slice expr) is taken from the spec and
the examples in the spec.
This is a trial run. The plan, probably for Go 1.8,
is to change slice expressions to use Node.List
instead of OKEY, and to do some similar
tree structure changes for other ops.
Passes toolstash -cmp. No performance change.
all.bash passes with GO_GCFLAGS=-newexport.
Updates #15350
Change-Id: Ic1efdc36e79cdb95ae1636e9817a3ac8f83ab1ac
Reviewed-on: https://go-review.googlesource.com/22425
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 04ccfad..e8fee67 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1241,35 +1241,28 @@
case ORECV:
Fatalf("walkexpr ORECV") // should see inside OAS only
- case OSLICE, OSLICEARR, OSLICESTR:
+ case OSLICE, OSLICEARR, OSLICESTR, OSLICE3, OSLICE3ARR:
n.Left = walkexpr(n.Left, init)
- n.Right.Left = walkexpr(n.Right.Left, init)
- if n.Right.Left != nil && iszero(n.Right.Left) {
- // Reduce x[0:j] to x[:j].
- n.Right.Left = nil
+ low, high, max := n.SliceBounds()
+ low = walkexpr(low, init)
+ if low != nil && iszero(low) {
+ // Reduce x[0:j] to x[:j] and x[0:j:k] to x[:j:k].
+ low = nil
}
- n.Right.Right = walkexpr(n.Right.Right, init)
- n = reduceSlice(n)
-
- case OSLICE3, OSLICE3ARR:
- n.Left = walkexpr(n.Left, init)
- n.Right.Left = walkexpr(n.Right.Left, init)
- if n.Right.Left != nil && iszero(n.Right.Left) {
- // Reduce x[0:j:k] to x[:j:k].
- n.Right.Left = nil
- }
- n.Right.Right.Left = walkexpr(n.Right.Right.Left, init)
- n.Right.Right.Right = walkexpr(n.Right.Right.Right, init)
-
- r := n.Right.Right.Right
- if r != nil && r.Op == OCAP && samesafeexpr(n.Left, r.Left) {
- // Reduce x[i:j:cap(x)] to x[i:j].
- n.Right.Right = n.Right.Right.Left
- if n.Op == OSLICE3 {
- n.Op = OSLICE
- } else {
- n.Op = OSLICEARR
+ high = walkexpr(high, init)
+ max = walkexpr(max, init)
+ n.SetSliceBounds(low, high, max)
+ if n.Op.IsSlice3() {
+ if max != nil && max.Op == OCAP && samesafeexpr(n.Left, max.Left) {
+ // Reduce x[i:j:cap(x)] to x[i:j].
+ if n.Op == OSLICE3 {
+ n.Op = OSLICE
+ } else {
+ n.Op = OSLICEARR
+ }
+ n = reduceSlice(n)
}
+ } else {
n = reduceSlice(n)
}
@@ -1425,8 +1418,9 @@
a := Nod(OAS, var_, nil) // zero temp
a = typecheck(a, Etop)
init.Append(a)
- r := Nod(OSLICE, var_, Nod(OKEY, nil, l)) // arr[:l]
- r = conv(r, n.Type) // in case n.Type is named.
+ r := Nod(OSLICE, var_, nil) // arr[:l]
+ r.SetSliceBounds(nil, l, nil)
+ r = conv(r, n.Type) // in case n.Type is named.
r = typecheck(r, Erv)
r = walkexpr(r, init)
n = r
@@ -1596,13 +1590,15 @@
return n
}
+// TODO(josharian): combine this with its caller and simplify
func reduceSlice(n *Node) *Node {
- r := n.Right.Right
- if r != nil && r.Op == OLEN && samesafeexpr(n.Left, r.Left) {
+ low, high, max := n.SliceBounds()
+ if high != nil && high.Op == OLEN && samesafeexpr(n.Left, high.Left) {
// Reduce x[i:len(x)] to x[i:].
- n.Right.Right = nil
+ high = nil
}
- if (n.Op == OSLICE || n.Op == OSLICESTR) && n.Right.Left == nil && n.Right.Right == nil {
+ n.SetSliceBounds(low, high, max)
+ if (n.Op == OSLICE || n.Op == OSLICESTR) && low == nil && high == nil {
// Reduce x[:] to x.
if Debug_slice > 0 {
Warn("slice: omit slice operation")
@@ -2816,14 +2812,15 @@
l = append(l, nif)
// s = s[:n]
- nt := Nod(OSLICE, s, Nod(OKEY, nil, nn))
+ nt := Nod(OSLICE, s, nil)
+ nt.SetSliceBounds(nil, nn, nil)
nt.Etype = 1
l = append(l, Nod(OAS, s, nt))
if haspointers(l1.Type.Elem()) {
// copy(s[len(l1):], l2)
- nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), nil))
-
+ nptr1 := Nod(OSLICE, s, nil)
+ nptr1.SetSliceBounds(Nod(OLEN, l1, nil), nil, nil)
nptr1.Etype = 1
nptr2 := l2
fn := syslook("typedslicecopy")
@@ -2835,8 +2832,8 @@
} else if instrumenting {
// rely on runtime to instrument copy.
// copy(s[len(l1):], l2)
- nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), nil))
-
+ nptr1 := Nod(OSLICE, s, nil)
+ nptr1.SetSliceBounds(Nod(OLEN, l1, nil), nil, nil)
nptr1.Etype = 1
nptr2 := l2
var fn *Node
@@ -2950,7 +2947,8 @@
nn := temp(Types[TINT])
l = append(l, Nod(OAS, nn, Nod(OLEN, ns, nil))) // n = len(s)
- nx = Nod(OSLICE, ns, Nod(OKEY, nil, Nod(OADD, nn, na))) // ...s[:n+argc]
+ nx = Nod(OSLICE, ns, nil) // ...s[:n+argc]
+ nx.SetSliceBounds(nil, Nod(OADD, nn, na), nil)
nx.Etype = 1
l = append(l, Nod(OAS, ns, nx)) // s = s[:n+argc]
