ssa: fix slice high

ssa/datastruct.go

@@ -333,6 +333,7 @@ func (b Builder) Slice(x, low, high, max Expr) (ret Expr) {
 	if debugInstr {
 		log.Printf("Slice %v, %v, %v\n", x.impl, low.impl, high.impl)
 	}
+
 	prog := b.Prog
 	var nCap Expr
 	var nEltSize Expr
@@ -356,7 +357,7 @@ func (b Builder) Slice(x, low, high, max Expr) (ret Expr) {
 		nEltSize = SizeOf(prog, prog.Index(x.Type))
 		nCap = b.SliceCap(x)
 		if high.IsNil() {
-			high = b.SliceCap(x)
+			high = b.SliceLen(x)
 		}
 		ret.Type = x.Type
 		base = b.SliceData(x)