RFA: let __extension__ suppress overlength string warning

[Tom Tromey <tromey at redhat dot com>]

SystemTap has some macros that can cause long strings to be generated.
See:

    http://sourceware.org/bugzilla/show_bug.cgi?id=12137

The usual system header exception does not suppress the
overlength-string warning here because the string results from a macro
expansion.  While Dodji's pending patch series promises to be able to
fix this, it seemed to me that __extension__ should also be able to do
this directly.

This patch changes the C parser to suppress the -Woverlength-strings
warning when the string is preceded by __extension__.

Built and regtested on x86-64 (compile farm).
New tests included.

Ok?

If approved, I assume I need to wait for stage 1 to commit this.

Tom

2011-01-18  Tom Tromey  <tromey@redhat.com>

	* c-parser.c (disable_extension_diagnostics): Save
	warn_overlength_strings.
	(restore_extension_diagnostics): Restore warn_overlength_strings.

2011-01-18  Tom Tromey  <tromey@redhat.com>

	* gcc.dg/Woverlength-strings-pedantic-c89-ext.c: New file.
	* gcc.dg/Woverlength-strings-pedantic-c90-ext.c: New file.
	* gcc.dg/Woverlength-strings-pedantic-c99-ext.c: New file.

Index: c-parser.c
===================================================================
--- c-parser.c	(revision 168933)
+++ c-parser.c	(working copy)
@@ -1045,13 +1045,15 @@
 	     | (warn_traditional << 2)
 	     | (flag_iso << 3)
 	     | (warn_long_long << 4)
-	     | (warn_cxx_compat << 5));
+	     | (warn_cxx_compat << 5)
+	     | (warn_overlength_strings << 6));
   cpp_opts->cpp_pedantic = pedantic = 0;
   warn_pointer_arith = 0;
   cpp_opts->cpp_warn_traditional = warn_traditional = 0;
   flag_iso = 0;
   cpp_opts->cpp_warn_long_long = warn_long_long = 0;
   warn_cxx_compat = 0;
+  warn_overlength_strings = 0;
   return ret;
 }
 
@@ -1067,6 +1069,7 @@
   flag_iso = (flags >> 3) & 1;
   cpp_opts->cpp_warn_long_long = warn_long_long = (flags >> 4) & 1;
   warn_cxx_compat = (flags >> 5) & 1;
+  warn_overlength_strings = (flags >> 6) & 1;
 }
 
 /* Possibly kinds of declarator to parse.  */
Index: testsuite/gcc.dg/Woverlength-strings-pedantic-c89-ext.c
===================================================================
--- testsuite/gcc.dg/Woverlength-strings-pedantic-c89-ext.c	(revision 0)
+++ testsuite/gcc.dg/Woverlength-strings-pedantic-c89-ext.c	(revision 0)
@@ -0,0 +1,19 @@
+/* -Woverlength-strings complains about string constants which are too long
+   for the C standard's "minimum maximum" limits.  It is off by default,
+   but implied by -pedantic.  */
+
+/* { dg-options "-std=c89 -pedantic" } */
+
+#define TEN "xxxxxxxxxx"
+#define HUN TEN TEN TEN TEN TEN  TEN TEN TEN TEN TEN
+#define THO HUN HUN HUN HUN HUN  HUN HUN HUN HUN HUN
+
+/* C89's minimum-maximum is 509. */
+const char x510[] = __extension__ HUN HUN HUN HUN HUN TEN;
+
+/* C99's minimum-maximum is 4095.  */
+const char x4096[] = __extension__
+  THO THO THO THO     /* 4000 */
+  TEN TEN TEN TEN TEN /* 4050 */
+  TEN TEN TEN TEN     /* 4090 */
+  "123456";
Index: testsuite/gcc.dg/Woverlength-strings-pedantic-c90-ext.c
===================================================================
--- testsuite/gcc.dg/Woverlength-strings-pedantic-c90-ext.c	(revision 0)
+++ testsuite/gcc.dg/Woverlength-strings-pedantic-c90-ext.c	(revision 0)
@@ -0,0 +1,19 @@
+/* -Woverlength-strings complains about string constants which are too long
+   for the C standard's "minimum maximum" limits.  It is off by default,
+   but implied by -pedantic.  */
+
+/* { dg-options "-std=c90 -pedantic" } */
+
+#define TEN "xxxxxxxxxx"
+#define HUN TEN TEN TEN TEN TEN  TEN TEN TEN TEN TEN
+#define THO HUN HUN HUN HUN HUN  HUN HUN HUN HUN HUN
+
+/* C89's minimum-maximum is 509. */
+const char x510[] = __extension__ HUN HUN HUN HUN HUN TEN;
+
+/* C99's minimum-maximum is 4095.  */
+const char x4096[] = __extension__
+  THO THO THO THO     /* 4000 */
+  TEN TEN TEN TEN TEN /* 4050 */
+  TEN TEN TEN TEN     /* 4090 */
+  "123456";
Index: testsuite/gcc.dg/Woverlength-strings-pedantic-c99-ext.c
===================================================================
--- testsuite/gcc.dg/Woverlength-strings-pedantic-c99-ext.c	(revision 0)
+++ testsuite/gcc.dg/Woverlength-strings-pedantic-c99-ext.c	(revision 0)
@@ -0,0 +1,19 @@
+/* -Woverlength-strings complains about string constants which are too long
+   for the C standard's "minimum maximum" limits.  It is off by default,
+   but implied by -pedantic.  */
+
+/* { dg-options "-std=c99 -pedantic" } */
+
+#define TEN "xxxxxxxxxx"
+#define HUN TEN TEN TEN TEN TEN  TEN TEN TEN TEN TEN
+#define THO HUN HUN HUN HUN HUN  HUN HUN HUN HUN HUN
+
+/* C89's minimum-maximum is 509. */
+const char x510[] = HUN HUN HUN HUN HUN TEN;
+
+/* C99's minimum-maximum is 4095.  */
+const char x4096[] = __extension__
+  THO THO THO THO     /* 4000 */
+  TEN TEN TEN TEN TEN /* 4050 */
+  TEN TEN TEN TEN     /* 4090 */
+  "123456";