cmd/compile: implement unsafe.Add and unsafe.Slice

Updates #19367.
Updates #40481.

Change-Id: Iabd2afdd0d520e5d68fd9e6dedd013335a4b3886
Reviewed-on: https://go-review.googlesource.com/c/go/+/312214
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>

2 files changed, 45 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/walk/builtin.go b/src/cmd/compile/internal/walk/builtin.go
index aacdedcb4d..62eb4298f4 100644
--- a/src/cmd/compile/internal/walk/builtin.go
+++ b/src/cmd/compile/internal/walk/builtin.go
@@ -653,6 +653,45 @@ func walkRecover(nn *ir.CallExpr, init *ir.Nodes) ir.Node {
 	return mkcall("gorecover", nn.Type(), init, fp)
 }
 
+func walkUnsafeSlice(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
+	len := safeExpr(n.Y, init)
+
+	fnname := "unsafeslice64"
+	argtype := types.Types[types.TINT64]
+
+	// Type checking guarantees that TIDEAL len/cap are positive and fit in an int.
+	// The case of len or cap overflow when converting TUINT or TUINTPTR to TINT
+	// will be handled by the negative range checks in unsafeslice during runtime.
+	if len.Type().IsKind(types.TIDEAL) || len.Type().Size() <= types.Types[types.TUINT].Size() {
+		fnname = "unsafeslice"
+		argtype = types.Types[types.TINT]
+	}
+
+	t := n.Type()
+
+	// Call runtime.unsafeslice[64] to check that the length argument is
+	// non-negative and smaller than the max length allowed for the
+	// element type.
+	fn := typecheck.LookupRuntime(fnname)
+	init.Append(mkcall1(fn, nil, init, reflectdata.TypePtr(t.Elem()), typecheck.Conv(len, argtype)))
+
+	ptr := walkExpr(n.X, init)
+
+	c := ir.NewUnaryExpr(n.Pos(), ir.OCHECKNIL, ptr)
+	c.SetTypecheck(1)
+	init.Append(c)
+
+	// TODO(mdempsky): checkptr instrumentation. Maybe merge into length
+	// check above, along with nil check? Need to be careful about
+	// notinheap pointers though: can't pass them as unsafe.Pointer.
+
+	h := ir.NewSliceHeaderExpr(n.Pos(), t,
+		typecheck.Conv(ptr, types.Types[types.TUNSAFEPTR]),
+		typecheck.Conv(len, types.Types[types.TINT]),
+		typecheck.Conv(len, types.Types[types.TINT]))
+	return walkExpr(typecheck.Expr(h), init)
+}
+
 func badtype(op ir.Op, tl, tr *types.Type) {
 	var s string
 	if tl != nil {
diff --git a/src/cmd/compile/internal/walk/expr.go b/src/cmd/compile/internal/walk/expr.go
index 5a1a2441bf..2fb907710b 100644
--- a/src/cmd/compile/internal/walk/expr.go
+++ b/src/cmd/compile/internal/walk/expr.go
@@ -117,12 +117,17 @@ func walkExpr1(n ir.Node, init *ir.Nodes) ir.Node {
 		n.X = walkExpr(n.X, init)
 		return n
 
-	case ir.OEFACE, ir.OAND, ir.OANDNOT, ir.OSUB, ir.OMUL, ir.OADD, ir.OOR, ir.OXOR, ir.OLSH, ir.ORSH:
+	case ir.OEFACE, ir.OAND, ir.OANDNOT, ir.OSUB, ir.OMUL, ir.OADD, ir.OOR, ir.OXOR, ir.OLSH, ir.ORSH,
+		ir.OUNSAFEADD:
 		n := n.(*ir.BinaryExpr)
 		n.X = walkExpr(n.X, init)
 		n.Y = walkExpr(n.Y, init)
 		return n
 
+	case ir.OUNSAFESLICE:
+		n := n.(*ir.BinaryExpr)
+		return walkUnsafeSlice(n, init)
+
 	case ir.ODOT, ir.ODOTPTR:
 		n := n.(*ir.SelectorExpr)
 		return walkDot(n, init)