[dev.link] all: merge branch 'master' into dev.link

Clean merge.

Change-Id: I94d5e621b98cd5b3e1f2007db83d52293edbd9ec

src/cmd/compile/internal/gc/main.go

@@ -40,6 +40,7 @@ var (
 
 var (
 	Debug_append       int
+	Debug_checkptr     int
 	Debug_closure      int
 	Debug_compilelater int
 	debug_dclstack     int
@@ -65,6 +66,7 @@ var debugtab = []struct {
 	val  interface{} // must be *int or *string
 }{
 	{"append", "print information about append compilation", &Debug_append},
+	{"checkptr", "instrument unsafe pointer conversions", &Debug_checkptr},
 	{"closure", "print information about closure compilation", &Debug_closure},
 	{"compilelater", "compile functions as late as possible", &Debug_compilelater},
 	{"disablenil", "disable nil checks", &disable_checknil},
@@ -435,6 +437,11 @@ func Main(archInit func(*Arch)) {
 		}
 	}
 
+	// Runtime can't use -d=checkptr, at least not yet.
+	if compiling_runtime {
+		Debug_checkptr = 0
+	}
+
 	// set via a -d flag
 	Ctxt.Debugpcln = Debug_pctab
 	if flagDWARF {