libgo patch committed: Avoid write barriers when calling deferred function

[Ian Lance Taylor]

Calling a deferred function in libgo currently requires changing from
a uintptr to the function code to a Go function value. That is done by
setting the value of a func local variable using unsafe.Pointer. The
local variable will always be on the stack. Adjust the code that sets
the local variable to avoid generating a write barrier.

A write barrier is never needed here. Also, for deferreturn, we must
avoid write barriers entirely when called from a cgo function; that
requires more than just this, but this is a start.

The test for this is runtime tests that use the go tool; these are not
currently run, but they will be in the future.

Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.  Committed
to mainline.

Ian

Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE     (revision 249558)
+++ gcc/go/gofrontend/MERGE     (working copy)
@@ -1,4 +1,4 @@
-a459f1fdfe0bd365bf2def730e1529052c6487fd
+73b14da15ec731837ce2a45db658142bfbf5fe22
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
Index: libgo/go/runtime/panic.go
===================================================================
--- libgo/go/runtime/panic.go   (revision 249558)
+++ libgo/go/runtime/panic.go   (working copy)
@@ -194,7 +194,7 @@ func deferreturn(frame *bool) {
                        // The gc compiler does this using assembler
                        // code in jmpdefer.
                        var fn func(unsafe.Pointer)
-                       *(**uintptr)(unsafe.Pointer(&fn)) = &pfn
+                       *(*uintptr)(unsafe.Pointer(&fn)) = 
uintptr(unsafe.Pointer(&pfn))
                        fn(d.arg)
                }
 
@@ -259,7 +259,7 @@ func checkdefer(frame *bool) {
                        gp._defer = d.link
 
                        var fn func(unsafe.Pointer)
-                       *(**uintptr)(unsafe.Pointer(&fn)) = &pfn
+                       *(*uintptr)(unsafe.Pointer(&fn)) = 
uintptr(unsafe.Pointer(&pfn))
                        fn(d.arg)
 
                        freedefer(d)
@@ -345,7 +345,7 @@ func Goexit() {
 
                if pfn != 0 {
                        var fn func(unsafe.Pointer)
-                       *(**uintptr)(unsafe.Pointer(&fn)) = &pfn
+                       *(*uintptr)(unsafe.Pointer(&fn)) = 
uintptr(unsafe.Pointer(&pfn))
                        fn(d.arg)
                }
 
@@ -446,7 +446,7 @@ func gopanic(e interface{}) {
 
                if pfn != 0 {
                        var fn func(unsafe.Pointer)
-                       *(**uintptr)(unsafe.Pointer(&fn)) = &pfn
+                       *(*uintptr)(unsafe.Pointer(&fn)) = 
uintptr(unsafe.Pointer(&pfn))
                        fn(d.arg)
 
                        if p.recovered {