libgo: update to Go1.10beta1

    
    Update the Go library to the 1.10beta1 release.
    
    Requires a few changes to the compiler for modifications to the map
    runtime code, and to handle some nowritebarrier cases in the runtime.
    
    Reviewed-on: https://go-review.googlesource.com/86455

gotools/:
	* Makefile.am (go_cmd_vet_files): New variable.
	(go_cmd_buildid_files, go_cmd_test2json_files): New variables.
	(s-zdefaultcc): Change from constants to functions.
	(noinst_PROGRAMS): Add vet, buildid, and test2json.
	(cgo$(EXEEXT)): Link against $(LIBGOTOOL).
	(vet$(EXEEXT)): New target.
	(buildid$(EXEEXT)): New target.
	(test2json$(EXEEXT)): New target.
	(install-exec-local): Install all $(noinst_PROGRAMS).
	(uninstall-local): Uninstasll all $(noinst_PROGRAMS).
	(check-go-tool): Depend on $(noinst_PROGRAMS).  Copy down
	objabi.go.
	(check-runtime): Depend on $(noinst_PROGRAMS).
	(check-cgo-test, check-carchive-test): Likewise.
	(check-vet): New target.
	(check): Depend on check-vet.  Look at cmd_vet-testlog.
	(.PHONY): Add check-vet.
	* Makefile.in: Rebuild.

From-SVN: r256365

1 files changed, 12 insertions, 4 deletions

diff --git a/libgo/go/runtime/cgo_gccgo.go b/libgo/go/runtime/cgo_gccgo.go
index c3bf9552ea8..05be4964500 100644
--- a/libgo/go/runtime/cgo_gccgo.go
+++ b/libgo/go/runtime/cgo_gccgo.go
@@ -27,6 +27,13 @@ var iscgo bool
 // The extra M must be created before any C/C++ code calls cgocallback.
 var cgoHasExtraM bool
 
+// cgoAlwaysFalse is a boolean value that is always false.
+// The cgo-generated code says if cgoAlwaysFalse { cgoUse(p) }.
+// The compiler cannot see that cgoAlwaysFalse is always false,
+// so it emits the test and keeps the call, giving the desired
+// escape analysis result. The test is cheaper than the call.
+var cgoAlwaysFalse bool
+
 // Cgocall prepares to call from code written in Go to code written in
 // C/C++. This takes the current goroutine out of the Go scheduler, as
 // though it were making a system call. Otherwise the program can
@@ -37,12 +44,11 @@ var cgoHasExtraM bool
 //     defer syscall.Cgocalldone()
 //     cfunction()
 func Cgocall() {
-	lockOSThread()
 	mp := getg().m
 	mp.ncgocall++
 	mp.ncgo++
-	mp.incgo = true
 	entersyscall(0)
+	mp.incgo = true
 }
 
 // CgocallDone prepares to return to Go code from C/C++ code.
@@ -59,8 +65,6 @@ func CgocallDone() {
 	if readgstatus(gp)&^_Gscan == _Gsyscall {
 		exitsyscall(0)
 	}
-
-	unlockOSThread()
 }
 
 // CgocallBack is used when calling from C/C++ code into Go code.
@@ -78,6 +82,8 @@ func CgocallBack() {
 		mp.dropextram = true
 	}
 
+	lockOSThread()
+
 	exitsyscall(0)
 	gp.m.incgo = false
 
@@ -100,6 +106,8 @@ func CgocallBack() {
 // CgocallBackDone prepares to return to C/C++ code that has called
 // into Go code.
 func CgocallBackDone() {
+	unlockOSThread()
+
 	// If we are the top level Go function called from C/C++, then
 	// we need to release the m. But don't release it if we are
 	// panicing; since this is the top level, we are going to