attempt to instrument the compiler for causal profiling

causalprof_compiler.diff

diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index dc3fb64e27..21e211e339 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -27,6 +27,7 @@ import (
 	"path"
 	"regexp"
 	"runtime"
+	"runtime/causalprof"
 	"strconv"
 	"strings"
 )
@@ -129,6 +130,18 @@ var nowritebarrierrecCheck *nowritebarrierrecChecker
 // arguments, type-checks the parsed Go package, compiles functions to machine
 // code, and finally writes the compiled package definition to disk.
 func Main(archInit func(*Arch)) {
+	cpfile := os.Getenv("CPFILE")
+	if cpfile != "" {
+		f, err := os.Create(cpfile)
+		if err != nil {
+			Fatalf("%v", err)
+		}
+		if err := causalprof.Start(f); err != nil {
+			Fatalf("%v", err)
+		}
+		atExit(causalprof.Stop)
+	}
+
 	timings.Start("fe", "init")
 
 	defer hidePanic()
@@ -682,7 +695,9 @@ func Main(archInit func(*Arch)) {
 		fninit(xtop)
 	}
 
+	progress := causalprof.StartProgress()
 	compileFunctions()
+	progress.Stop()
 
 	if nowritebarrierrecCheck != nil {
 		// Write barriers are now known. Check the