Hi,
this has bothered me for some time. The gcc configure with stage1 feels
like taking forever because some of the decl availability tests (checking
for C function) include system.h, and that, since a while, unconditionally
includes <string> and <algorithm> under C++, and we meanwhile use the C++
compiler for configure tests (which makes sense). Now, the difference for
a debuggable (but not even checking-enabled) cc1plus for a file containing
just main():
% cat blaeh.cc
#include <stdio.h>
#include <cstring>
#include <utility>
#include <new>
int main() {}
% cc1plus -quiet -ftime-report blaeh.cc
TOTAL : 0.12 0.01 0.14
(This is btw. three times as expensive as with 4.8 headers (i.e.
precompile with g++-4.8 then compile with the same cc1plus as above,
taking 0.04 seconds; the STL headers bloat quite much over time)
Well, not quite blazing fast but then adding <string>:
% cc1plus -quiet -ftime-report blaeh-string.cc
TOTAL : 0.60 0.05 0.66
Meeh. And adding <algorithm> on top:
% cc1plus -quiet -ftime-report blaeh-string-alg.cc
TOTAL : 1.13 0.09 1.23
So, more than a second for checking if some C-only decl is available, just
because system.h unconditionally includes mostly useless STL headers.
So, how useless exactly? A whopping single file of cc1 proper needs
<string>, _two_ files need <algorithm>, and a single target has an unlucky
interface in its prototypes and also needs <string>. (One additional
header lazily uses std::string for no particular reason). So we pay about
5 minutes build time per stage (there are ~400 libbackend.a files) for
more or less nothing.
So, let's include those headers only conditionally; I'm pretty sure it's
not unreasonable for a source file, if it needs a particular STL facility
to #define USES_abcheader (like one normally would have to #include
<abcheader>) before the "system.h" include.
See the patch. I've grepped for target or language dependencies on other
STL types, and either they were already including the right header, or
were covered with the new system.h (i.e. I've built all targets quickly
for which grepping for 'std::' returned anything). The genconditions.c
change is for the benefit of aarch64 as well, and it single function
aarch64_get_extension_string_for_isa_flags returning a std::string.
What do people think? Should I pass it through a proper bootstrap and put
it to trunk? It's a (developer time) regression, right? ;-)
Ciao,
Michael.
* system.h (string, algorithm): Include only conditionally.
(new): Include always under C++.
* bb-reorder.c (toplevel): Define USES_ALGORITHM.
* final.c (toplevel): Ditto.
* ipa-chkp.c (toplevel): Define USES_STRING.
* genconditions.c (write_header): Make gencondmd.c define
USES_STRING.
* mem-stats.h (mem_usage::print_dash_line): Don't use std::string.
* config/aarch64/aarch64.c (toplevel): Define USES_STRING.
* common/config/aarch64/aarch64-common.c (toplevel): Ditto.
Index: bb-reorder.c
===================================================================
--- bb-reorder.c (revision 232675)
+++ bb-reorder.c (working copy)
@@ -91,6 +91,7 @@
*/
#include "config.h"
+#define USES_ALGORITHM /* stable_sort */
#include "system.h"
#include "coretypes.h"
#include "backend.h"
Index: final.c
===================================================================
--- final.c (revision 232675)
+++ final.c (working copy)
@@ -43,6 +43,7 @@ along with GCC; see the file COPYING3.
function_epilogue. Those instructions never exist as rtl. */
#include "config.h"
+#define USES_ALGORITHM /* reverse */
#include "system.h"
#include "coretypes.h"
#include "backend.h"
Index: genconditions.c
===================================================================
--- genconditions.c (revision 232675)
+++ genconditions.c (working copy)
@@ -51,6 +51,7 @@ write_header (void)
machine description file. */\n\
\n\
#include \"bconfig.h\"\n\
+#define USES_STRING\n\
#include \"system.h\"\n\
\n\
/* It is necessary, but not entirely safe, to include the headers below\n\
Index: ipa-chkp.c
===================================================================
--- ipa-chkp.c (revision 232675)
+++ ipa-chkp.c (working copy)
@@ -19,6 +19,7 @@ along with GCC; see the file COPYING3.
<http://www.gnu.org/licenses/>. */
#include "config.h"
+#define USES_STRING
#include "system.h"
#include "coretypes.h"
#include "backend.h"
Index: mem-stats.h
===================================================================
--- mem-stats.h (revision 232675)
+++ mem-stats.h (working copy)
@@ -200,7 +200,9 @@ struct mem_usage
static inline void
print_dash_line (size_t count = 140)
{
- fprintf (stderr, "%s\n", std::string (count, '-').c_str ());
+ while (count--)
+ fputc ('-', stderr);
+ fputc ('\n', stderr);
}
/* Dump header with NAME. */
Index: system.h
===================================================================
--- system.h (revision 232675)
+++ system.h (working copy)
@@ -198,8 +198,10 @@ extern int fprintf_unlocked (FILE *, con
the ctype macros through safe-ctype.h */
#ifdef __cplusplus
+#ifdef USES_STRING
# include <string>
#endif
+#endif
/* There are an extraordinary number of issues with <ctype.h>.
The last straw is that it varies with the locale. Use libiberty's
@@ -215,8 +217,11 @@ extern int errno;
#endif
#ifdef __cplusplus
+#ifdef USES_ALGORITHM
# include <algorithm>
+#endif
# include <cstring>
+# include <new>
# include <utility>
#endif
Index: config/aarch64/aarch64.c
===================================================================
--- config/aarch64/aarch64.c (revision 232675)
+++ config/aarch64/aarch64.c (working copy)
@@ -19,6 +19,7 @@
<http://www.gnu.org/licenses/>. */
#include "config.h"
+#define USES_STRING
#include "system.h"
#include "coretypes.h"
#include "backend.h"
Index: common/config/aarch64/aarch64-common.c
===================================================================
--- common/config/aarch64/aarch64-common.c (revision 232675)
+++ common/config/aarch64/aarch64-common.c (working copy)
@@ -19,6 +19,7 @@
<http://www.gnu.org/licenses/>. */
#include "config.h"
+#define USES_STRING
#include "system.h"
#include "coretypes.h"
#include "tm.h"
