cmd/compile: use autogenerated position for init functions

This eliminates an old TODO,
and stabilizes the position information
for init functions.

Change-Id: Idf2d9a16a60e097ee08f42541b87e170da2f9d3a
Reviewed-on: https://go-review.googlesource.com/38388
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -4,6 +4,8 @@
 
 package gc
 
+import "cmd/internal/src"
+
 // a function named init is a special case.
 // it is called by the initialization before
 // main is run. to make it unique within a
@@ -75,9 +77,7 @@ func anyinit(n []*Node) bool {
 }
 
 func fninit(n []*Node) {
-	// This code is using the last value of lineno for position information
-	// (see comment in noder.go, noder.file method, for details).
-
+	lineno = makePos(src.NewFileBase("<autogenerated>", "<autogenerated>"), 1, 0)
 	nf := initfix(n)
 	if !anyinit(nf) {
 		return

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

@@ -101,18 +101,7 @@ func (p *noder) node() {
 	}
 
 	pragcgobuf += p.pragcgobuf
-
-	// For compatibility with old code only (comparisons w/ toolstash):
-	// The old line number tracking simply continued incrementing the
-	// virtual line number (lexlineno) and using it also for lineno.
-	// After processing the last function, the lineno was used for the
-	// line number information of the initialization code (fninit).
-	// It would be better to use an explicit "<autogenerated>" filename
-	// for fninit and set lineno to NoPos here.
-	// TODO(gri) fix this once we switched permanently to the new
-	// position information.
-	lineno = makePos(p.file.Pos().Base(), uint(p.file.Lines), 0)
-
+	lineno = src.NoXPos
 	clearImports()
 }