cmd/compile/internal/gc: document variables and functions

Change-Id: I01b2278eb50585331b8ff7ff5e3c1f9c5ba52b63
Reviewed-on: https://go-review.googlesource.com/33156Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -119,8 +119,12 @@ var linkobj string
 
 var bout *bio.Writer
 
+// nerrors is the number of compiler errors reported
+// since the last call to saveerrors.
 var nerrors int
 
+// nsavederrors is the total number of compiler errors
+// reported before the last call to saveerrors.
 var nsavederrors int
 
 var nsyntaxerrors int

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

@@ -98,6 +98,9 @@ func supportsDynlink(arch *sys.Arch) bool {
 var timings Timings
 var benchfile string
 
+// Main parses flags and Go source files specified in the command-line
+// arguments, type-checks the parsed Go package, compiles functions to machine
+// code, and finally writes the compiled package definition to disk.
 func Main() {
 	timings.Start("fe", "init")
 
@@ -483,6 +486,7 @@ func Main() {
 		errorexit()
 	}
 
+	// Write object data to disk.
 	timings.Start("be", "dumpobj")
 	dumpobj()
 	if asmhdr != "" {

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

@@ -58,6 +58,8 @@ func (x byLineno) Len() int           { return len(x) }
 func (x byLineno) Less(i, j int) bool { return x[i].lineno < x[j].lineno }
 func (x byLineno) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
 
+// flusherrors sorts errors seen so far by line number, prints them to stdout,
+// and empties the errors array.
 func flusherrors() {
 	Ctxt.Bso.Flush()
 	if len(errors) == 0 {