From e3e043bea4d7547edf004a9e202f66a4d69b5899 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Martin=20M=C3=B6hrmann?= <moehrmann@google.com>
Date: Fri, 2 Nov 2018 14:38:33 +0100
Subject: [PATCH] cmd/compile: improve typechecking of OSLICEHEADER nodes
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Create a new node for OSLICEHEADER nodes to ensure typechecks are applied.
Add nil checks for OSLICEHEADER type and pointer parameters
for better error messages when these are not set.
Improve formatting of OSLICEHEADER nodes in compiler error messages.

Change-Id: Idea8f41bb4beb636f0e1fc381ff8d79b1d44fbae
Reviewed-on: https://go-review.googlesource.com/c/146997
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
---
 src/cmd/compile/internal/gc/fmt.go       |  7 +++++++
 src/cmd/compile/internal/gc/typecheck.go |  6 +++++-
 src/cmd/compile/internal/gc/walk.go      | 17 ++++++++++-------
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/cmd/compile/internal/gc/fmt.go b/src/cmd/compile/internal/gc/fmt.go
index 0f4b6c9936..16b81e6a88 100644
--- a/src/cmd/compile/internal/gc/fmt.go
+++ b/src/cmd/compile/internal/gc/fmt.go
@@ -1114,6 +1114,7 @@ var opprec = []int{
 	OSLICEARR:     8,
 	OSLICE3:       8,
 	OSLICE3ARR:    8,
+	OSLICEHEADER:  8,
 	ODOTINTER:     8,
 	ODOTMETH:      8,
 	ODOTPTR:       8,
@@ -1393,6 +1394,12 @@ func (n *Node) exprfmt(s fmt.State, prec int, mode fmtMode) {
 		}
 		fmt.Fprint(s, "]")
 
+	case OSLICEHEADER:
+		if n.List.Len() != 2 {
+			Fatalf("bad OSLICEHEADER list length %d", n.List.Len())
+		}
+		mode.Fprintf(s, "sliceheader{%v,%v,%v}", n.Left, n.List.First(), n.List.Second())
+
 	case OCOPY, OCOMPLEX:
 		mode.Fprintf(s, "%#v(%v, %v)", n.Op, n.Left, n.Right)
 
diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 8ec60cbbba..e6a8ed4bda 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -1160,11 +1160,15 @@ func typecheck1(n *Node, top int) (res *Node) {
 		ok |= Erv
 
 		t := n.Type
+		if t == nil {
+			Fatalf("no type specified for OSLICEHEADER")
+		}
+
 		if !t.IsSlice() {
 			Fatalf("invalid type %v for OSLICEHEADER", n.Type)
 		}
 
-		if !n.Left.Type.IsUnsafePtr() {
+		if n.Left == nil || n.Left.Type == nil || !n.Left.Type.IsUnsafePtr() {
 			Fatalf("need unsafe.Pointer for OSLICEHEADER")
 		}
 
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index f459cb3dec..fa0dcab5eb 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1351,14 +1351,17 @@ opswitch:
 				argtype = types.Types[TINT]
 			}
 
+			m := nod(OSLICEHEADER, nil, nil)
+			m.Type = t
+
 			fn := syslook(fnname)
-			n.Left = mkcall1(fn, types.Types[TUNSAFEPTR], init, typename(t.Elem()), conv(len, argtype), conv(cap, argtype))
-			n.Left.SetNonNil(true)
-			n.List.Set2(conv(len, types.Types[TINT]), conv(cap, types.Types[TINT]))
-			n.Op = OSLICEHEADER
-			n.Type = t
-			n = typecheck(n, Erv)
-			n = walkexpr(n, init)
+			m.Left = mkcall1(fn, types.Types[TUNSAFEPTR], init, typename(t.Elem()), conv(len, argtype), conv(cap, argtype))
+			m.Left.SetNonNil(true)
+			m.List.Set2(conv(len, types.Types[TINT]), conv(cap, types.Types[TINT]))
+
+			m = typecheck(m, Erv)
+			m = walkexpr(m, init)
+			n = m
 		}
 
 	case ORUNESTR:
-- 
2.50.0