From: Cherry Zhang <cherryyz@google.com>
Date: Mon, 29 Mar 2021 17:44:08 +0000 (-0400)
Subject: cmd/compile: check deferred nil interface call before wrapping it
X-Git-Tag: go1.17beta1~936
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=bd6628e62d;p=gostls13.git

cmd/compile: check deferred nil interface call before wrapping it

Currently, for "defer i.M()" if i is nil it panics at the point of
defer statement, not when deferred function is called. We need to
do the nil check before wrapping it.

Updates #40724.

Change-Id: I62c669264668991f71999e2cf4610a9066247f9d
Reviewed-on: https://go-review.googlesource.com/c/go/+/305549
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
---

diff --git a/src/cmd/compile/internal/walk/order.go b/src/cmd/compile/internal/walk/order.go
index 95d245d0d7..9e6c58054d 100644
--- a/src/cmd/compile/internal/walk/order.go
+++ b/src/cmd/compile/internal/walk/order.go
@@ -1602,6 +1602,17 @@ func (o *orderState) wrapGoDefer(n *ir.GoDeferStmt) {
 			n := callX.(*ir.SelectorExpr)
 			n.X = mkArgCopy(n.X)
 			methSelectorExpr = n
+			if callX.Op() == ir.ODOTINTER {
+				// Currently for "defer i.M()" if i is nil it panics at the
+				// point of defer statement, not when deferred function is called.
+				// (I think there is an issue discussing what is the intended
+				// behavior but I cannot find it.)
+				// We need to do the nil check outside of the wrapper.
+				tab := typecheck.Expr(ir.NewUnaryExpr(base.Pos, ir.OITAB, n.X))
+				c := ir.NewUnaryExpr(n.Pos(), ir.OCHECKNIL, tab)
+				c.SetTypecheck(1)
+				o.append(c)
+			}
 		case !(callX.Op() == ir.ONAME && callX.(*ir.Name).Class == ir.PFUNC):
 			// Deal with "defer returnsafunc()(x, y)" (for
 			// example) by copying the callee expression.