Patch: push_cfun -vs- in_system_header

[Tom Tromey <tromey at redhat dot com>]

This patch fixes PRs c++/32256 and c++/32368.  But, despite their
names, I think they are not C++ bugs per se, but rather a general
problem in the middle end.

The bug is that when a function is analyzed, in_system_header is not
properly set.  This leads gcc to emit warnings which should not be
emitted.  This can happen if, e.g., cgraph defers processing a
function in unit-at-a-time mode.

My fix is to save and restore in_system_header in push_cfun and
pop_cfun.  I think this is safe because these are used pairwise to
wrap code that should be run in the context of a particular function;
so using the function's notion of in_system_header here seems correct.

I tried instrumenting set_cfun instead, but that didn't work out.  It
is used in strange and unconstrained ways.  (Maybe it would be nice to
get rid of this.  And, FWIW, I noticed a couple places that still
assign directly to cfun... maybe we should make it a compile-time
error to use cfun as an lvalue?)

Bootstrapped and regtested on x86 FC-6.  Two new test cases included.
Ok?

Tom

:ADDPATCH middle-end:

ChangeLog:
2007-11-05  Tom Tromey  <tromey@redhat.com>

	PR c++/32256, PR c++/32368:
	* function.c (saved_in_system_header): New global.
	(push_cfun): Save in_system_header.
	(pop_cfun): Restore in_system_header.
	(push_struct_function): Save in_system_header.

testsuite/ChangeLog:
2007-11-05  Tom Tromey  <tromey@redhat.com>

	PR c++/32368:
	* g++.dg/warn/pragma-system_header3.h: New.
	* g++.dg/warn/pragma-system_header3.C: New.

	PR c++/32256:
	* g++.dg/warn/pragma-system_header4.C: New.
	* g++.dg/warn/pragma-system_header4.h: New.

Index: function.c
===================================================================
--- function.c	(revision 129850)
+++ function.c	(working copy)
@@ -3834,12 +3834,22 @@
 
 static VEC(function_p,heap) *cfun_stack;
 
+/* We save the value of in_system_header here when pushing the first
+   function on the cfun stack, and we restore it from here when
+   popping the last function.  */
+
+static bool saved_in_system_header;
+
 /* Push the current cfun onto the stack, and set cfun to new_cfun.  */
 
 void
 push_cfun (struct function *new_cfun)
 {
+  if (cfun == NULL)
+    saved_in_system_header = in_system_header;
   VEC_safe_push (function_p, heap, cfun_stack, cfun);
+  if (new_cfun)
+    in_system_header = DECL_IN_SYSTEM_HEADER (new_cfun->decl);
   set_cfun (new_cfun);
 }
 
@@ -3848,7 +3858,10 @@
 void
 pop_cfun (void)
 {
-  set_cfun (VEC_pop (function_p, cfun_stack));
+  struct function *new_cfun = VEC_pop (function_p, cfun_stack);
+  in_system_header = ((new_cfun == NULL) ? saved_in_system_header
+		      : DECL_IN_SYSTEM_HEADER (new_cfun->decl));
+  set_cfun (new_cfun);
 }
 
 /* Return value of funcdef and increase it.  */
@@ -3922,7 +3935,11 @@
 void
 push_struct_function (tree fndecl)
 {
+  if (cfun == NULL)
+    saved_in_system_header = in_system_header;
   VEC_safe_push (function_p, heap, cfun_stack, cfun);
+  if (fndecl)
+    in_system_header = DECL_IN_SYSTEM_HEADER (fndecl);
   allocate_struct_function (fndecl);
 }
 
Index: testsuite/g++.dg/warn/pragma-system_header3.C
===================================================================
--- testsuite/g++.dg/warn/pragma-system_header3.C	(revision 0)
+++ testsuite/g++.dg/warn/pragma-system_header3.C	(revision 0)
@@ -0,0 +1,9 @@
+// PR c++/32368
+// { dg-options "-Wall -O" }
+
+#include "pragma-system_header3.h"
+
+int main()
+{
+	return f();
+}
Index: testsuite/g++.dg/warn/pragma-system_header3.h
===================================================================
--- testsuite/g++.dg/warn/pragma-system_header3.h	(revision 0)
+++ testsuite/g++.dg/warn/pragma-system_header3.h	(revision 0)
@@ -0,0 +1,7 @@
+#pragma GCC system_header
+
+static inline int f()
+{
+	int i;
+	return i;
+}
Index: testsuite/g++.dg/warn/pragma-system_header4.C
===================================================================
--- testsuite/g++.dg/warn/pragma-system_header4.C	(revision 0)
+++ testsuite/g++.dg/warn/pragma-system_header4.C	(revision 0)
@@ -0,0 +1,6 @@
+// PR c++/32256
+// { dg-options "-Wall" }
+
+#include "pragma-system_header4.h"
+
+void ok() { }
Index: testsuite/g++.dg/warn/pragma-system_header4.h
===================================================================
--- testsuite/g++.dg/warn/pragma-system_header4.h	(revision 0)
+++ testsuite/g++.dg/warn/pragma-system_header4.h	(revision 0)
@@ -0,0 +1,2 @@
+#pragma GCC system_header
+int noreturn() { }