compiler: error on func declaration/definition

Long long long ago Go permitted writing
        func F()
    in one file and writing
        func F() {}
    in another file.  This was removed from the language, and that is now
    considered to be a multiple definition error.  Gccgo never caught up
    to that, and it has been permitting this invalid code for some time.
    
    Stop permitting it, so that we give correct errors.  Since we've
    supported it for a long time, the compiler uses it in a couple of
    cases: it predeclares the hash/equal methods if it decides to create
    them while compiling another function, and it predeclares main.main as
    a mechanism for getting the right warning if a program uses the wrong
    signature for main.  For simplicity, keep those existing uses.
    
    This required a few minor changes in libgo which were relying,
    unnecessarily, on the current behavior.
    
    Reviewed-on: https://go-review.googlesource.com/93083

From-SVN: r257600

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-cebdbf3f293f5b0f3120c009c47da0ceadc113cb
+7998e29eec43ede1cee925d87eef0b09da67d90b
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/gogo.cc

@@ -7762,33 +7762,29 @@ Bindings::new_definition(Named_object* old_object, Named_object* new_object)
       go_unreachable();
 
     case Named_object::NAMED_OBJECT_FUNC:
-      if (new_object->is_function_declaration())
-	{
-	  if (!new_object->func_declaration_value()->asm_name().empty())
-	    go_error_at(Linemap::unknown_location(),
-			("sorry, not implemented: "
-			 "__asm__ for function definitions"));
-	  Function_type* old_type = old_object->func_value()->type();
-	  Function_type* new_type =
-	    new_object->func_declaration_value()->type();
-	  if (old_type->is_valid_redeclaration(new_type, &reason))
-	    return old_object;
-	}
       break;
 
     case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
       {
-	if (new_object->is_function())
+	// We declare the hash and equality functions before defining
+	// them, because we sometimes see that we need the declaration
+	// while we are in the middle of a different function.  We
+	// declare the main function before the user defines it, to
+	// give better error messages.
+	if (new_object->is_function()
+	    && ((Linemap::is_predeclared_location(old_object->location())
+		 && Linemap::is_predeclared_location(new_object->location()))
+		|| (Gogo::unpack_hidden_name(old_object->name()) == "main"
+		    && Linemap::is_unknown_location(old_object->location()))))
 	  {
             Function_type* old_type =
                 old_object->func_declaration_value()->type();
 	    Function_type* new_type = new_object->func_value()->type();
 	    if (old_type->is_valid_redeclaration(new_type, &reason))
 	      {
-		if (!old_object->func_declaration_value()->asm_name().empty())
-		  go_error_at(Linemap::unknown_location(),
-			      ("sorry, not implemented: "
-			       "__asm__ for function definitions"));
+		Function_declaration* fd =
+		  old_object->func_declaration_value();
+		go_assert(fd->asm_name().empty());
 		old_object->set_function_value(new_object->func_value());
 		this->named_objects_.push_back(old_object);
 		return old_object;
@@ -7810,8 +7806,10 @@ Bindings::new_definition(Named_object* old_object, Named_object* new_object)
   old_object->set_is_redefinition();
   new_object->set_is_redefinition();
 
-  go_inform(old_object->location(), "previous definition of %qs was here",
-            n.c_str());
+  if (!Linemap::is_unknown_location(old_object->location())
+      && !Linemap::is_predeclared_location(old_object->location()))
+    go_inform(old_object->location(), "previous definition of %qs was here",
+	      n.c_str());
 
   return old_object;
 }

libgo/go/runtime/extern.go

@@ -157,10 +157,6 @@ package runtime
 
 import "runtime/internal/sys"
 
-// Gosched yields the processor, allowing other goroutines to run.  It does not
-// suspend the current goroutine, so execution resumes automatically.
-func Gosched()
-
 // Caller reports file and line number information about function invocations on
 // the calling goroutine's stack. The argument skip is the number of stack frames
 // to ascend, with 0 identifying the caller of Caller.  (For historical reasons the

libgo/go/runtime/stubs.go

@@ -306,10 +306,6 @@ func setSupportAES(v bool) {
 	support_aes = v
 }
 
-// Here for gccgo until we port lock_*.go.
-func lock(l *mutex)
-func unlock(l *mutex)
-
 // Here for gccgo.
 func errno() int
 
@@ -317,9 +313,6 @@ func errno() int
 func entersyscall(int32)
 func entersyscallblock(int32)
 
-// Here for gccgo until we port mgc.go.
-func GC()
-
 // For gccgo to call from C code, so that the C code and the Go code
 // can share the memstats variable for now.
 //go:linkname getMstats runtime.getMstats
@@ -327,16 +320,6 @@ func getMstats() *mstats {
 	return &memstats
 }
 
-// Temporary for gccgo until we port mem_GOOS.go.
-func sysAlloc(n uintptr, sysStat *uint64) unsafe.Pointer
-func sysFree(v unsafe.Pointer, n uintptr, sysStat *uint64)
-
-// Temporary for gccgo until we port malloc.go
-func persistentalloc(size, align uintptr, sysStat *uint64) unsafe.Pointer
-
-// Temporary for gccgo until we port mheap.go
-func setprofilebucket(p unsafe.Pointer, b *bucket)
-
 // Get signal trampoline, written in C.
 func getSigtramp() uintptr
 

libgo/misc/cgo/test/issue9400/gccgo.go

@@ -16,6 +16,8 @@ import (
 // without writing more assembly code, which we haven't bothered to
 // do.  So this is not much of a test.
 
+var Baton int32
+
 func RewindAndSetgid() {
 	atomic.StoreInt32(&Baton, 1)
 	for atomic.LoadInt32(&Baton) != 0 {

libgo/misc/cgo/test/issue9400/stubs.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !gccgo
+
 package issue9400
 
 var Baton int32