cmd/compile: don't let -race override explicit -d=checkptr=0

Change-Id: Icfa204761045b72a8ea173fd55eddf1f0e58d819
Reviewed-on: https://go-review.googlesource.com/c/go/+/304253
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Author: ianlancetaylor

Diff for: src/cmd/compile/internal/base/flag.go

@@ -161,6 +161,8 @@ func ParseFlags() {
 	Flag.WB = true
 	Debug.InlFuncsWithClosures = 1
 
+	Debug.Checkptr = -1 // so we can tell whether it is set explicitly
+
 	Flag.Cfg.ImportMap = make(map[string]string)
 
 	objabi.AddVersionFlag() // -V
@@ -216,7 +218,9 @@ func ParseFlags() {
 	}
 	if Flag.Race || Flag.MSan {
 		// -race and -msan imply -d=checkptr for now.
-		Debug.Checkptr = 1
+		if Debug.Checkptr == -1 { // if not set explicitly
+			Debug.Checkptr = 1
+		}
 	}
 
 	if Flag.CompilingRuntime && Flag.N != 0 {
@@ -237,6 +241,10 @@ func ParseFlags() {
 		Debug.Libfuzzer = 0
 	}
 
+	if Debug.Checkptr == -1 { // if not set explicitly
+		Debug.Checkptr = 0
+	}
+
 	// set via a -d flag
 	Ctxt.Debugpcln = Debug.PCTab
 }

Diff for: test/fixedbugs/bug513.go

@@ -0,0 +1,20 @@
+// run -race -gcflags=all=-d=checkptr=0
+// +build linux,amd64 linux,ppc64le darwin,amd64 freebsd,amd64 netbsd,amd64 windows,amd64
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Although -race turns on -d=checkptr, the explicit -d=checkptr=0
+// should override it.
+
+package main
+
+import "unsafe"
+
+var v1 = new([2]int16)
+var v2 *[3]int64
+
+func main() {
+	v2 = (*[3]int64)(unsafe.Pointer(uintptr(unsafe.Pointer(&(*v1)[0]))))
+}