[PCH] driver, documentation

[PCH] driver, documentation

[Geoffrey Keating]

This patch starts PCH support.  It adds support in the driver for
compiling headers, and documents how the PCH support will work.

Bootstrapped & tested on x86-linux.

-- 
Geoff Keating <geoffk@redhat.com>

===File ~/patches/pchbranch-driver.patch====================
Index: ChangeLog
2002-08-17  Geoffrey Keating  <geoffk@redhat.com>

	* c-common.c: (pch_file): Define.
	* c-common.h (pch_file): Declare.
	* c-opts.c (COMMAND_LINE_OPTIONS): Add --output-pch=.
	(missing_arg): Require --output-pch= to have an argument.
	(c_common_decode_option): Handle --output-pch=.
	* gcc.c: Document new %V.
	(default_compilers): Handle compiling C header files.
	(do_spec_1): Implement %V.
	(main): Handle "gcc foo.h" without trying to run linker.
	* doc/invoke.texi (Invoking GCC): Add new menu item for PCH.
	(Overall Options): Document what the driver does with header files,
	document new -x option possibilities.
	(Invoking G++): More documentation for PCH.
	(Precompiled Headers): New.

Index: cp/ChangeLog
2002-08-17  Geoffrey Keating  <geoffk@redhat.com>

	* g++spec.c (lang_specific_driver): Treat .h files as C++ header
	files when using g++.
	* lang-specs.h: Handle compiling C++ header files.

Index: c-common.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-common.c,v
retrieving revision 1.286.4.11
diff -p -u -p -r1.286.4.11 c-common.c
--- c-common.c	13 Aug 2002 17:56:13 -0000	1.286.4.11
+++ c-common.c	18 Aug 2002 00:21:06 -0000
@@ -197,6 +197,11 @@ tree c_global_trees[CTI_MAX];
 /* Nonzero if prepreprocessing only.  */
 int flag_preprocess_only;
 
+/* The filename to which we should write a precompiled header, or
+   NULL if no header will be written in this compile.  */
+
+const char *pch_file;
+
 /* Nonzero if an ISO standard was selected.  It rejects macros in the
    user's namespace.  */
 int flag_iso;
Index: c-common.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-common.h,v
retrieving revision 1.112.4.12
diff -p -u -p -r1.112.4.12 c-common.h
--- c-common.h	13 Aug 2002 17:56:13 -0000	1.112.4.12
+++ c-common.h	18 Aug 2002 00:21:06 -0000
@@ -373,6 +373,11 @@ extern c_language_kind c_language;
 /* Nonzero if prepreprocessing only.  */
 extern int flag_preprocess_only;
 
+/* The filename to which we should write a precompiled header, or
+   NULL if no header will be written in this compile.  */
+
+extern const char *pch_file;
+
 /* Nonzero if an ISO standard was selected.  It rejects macros in the
    user's namespace.  */
 extern int flag_iso;
Index: c-opts.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-opts.c,v
retrieving revision 1.10.2.1
diff -p -u -p -r1.10.2.1 c-opts.c
--- c-opts.c	13 Aug 2002 17:56:14 -0000	1.10.2.1
+++ c-opts.c	18 Aug 2002 00:21:07 -0000
@@ -79,6 +79,7 @@ static void handle_OPT_d PARAMS ((const 
 
 #define COMMAND_LINE_OPTIONS						     \
   OPT("-help",                  CL_ALL,   OPT__help)			     \
+  OPT("-output-pch=",		CL_ALL | CL_JOINED, OPT__output_pch)	     \
   OPT("C",                      CL_ALL,   OPT_C)			     \
   OPT("CC",                     CL_ALL,   OPT_CC)			     \
   OPT("E",			CL_ALL,   OPT_E)			     \
@@ -282,6 +283,7 @@ missing_arg (opt_index)
 {
   switch (opt_index)
     {
+    case OPT__output_pch:
     case OPT_Wformat_eq:
     case OPT_d:
     case OPT_fbuiltin_:
@@ -511,6 +513,10 @@ c_common_decode_option (argc, argv)
 
     case OPT__help:
       print_help ();
+      break;
+
+    case OPT__output_pch:
+      pch_file = xstrdup (arg + strlen ("--output-pch="));
       break;
 
     case OPT_C:
Index: gcc.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/gcc.c,v
retrieving revision 1.285.4.7
diff -p -u -p -r1.285.4.7 gcc.c
--- gcc.c	13 Aug 2002 17:56:31 -0000	1.285.4.7
+++ gcc.c	18 Aug 2002 00:21:07 -0000
@@ -382,6 +382,7 @@ or with constant text in a single argume
  %w	marks the argument containing or following the %w as the
 	"output file" of this compilation.  This puts the argument
 	into the sequence of arguments that %o will substitute later.
+ %V	indicates that this compilation produces no "output file".
  %W{...}
 	like %{...} but mark last argument supplied within
 	as a file to be deleted on failure.
@@ -845,8 +846,10 @@ static const struct compiler default_com
     %(trad_capable_cpp) %{ansi:-std=c89} %(cpp_options)", 0},
   {".h", "@c-header", 0},
   {"@c-header",
-   "%{!E:%ecompilation of header file requested} \
-    %(trad_capable_cpp) %{ansi:-std=c89} %(cpp_options) %(cpp_debug_options)",
+   "%{E|M|MM:%(trad_capable_cpp) -lang-c %{ansi:-std=c89} %(cpp_options) \
+      %(cpp_debug_options)}\
+    %{!E:cc1 %{ansi:-std=c89} %(cpp_unique_options) %(cc1_options) \
+     -o %g.s %{!o*:--output-pch=%i.pch} %W{^o*:--output-pch=%*}%V} ",
    0},
   {".i", "@cpp-output", 0},
   {"@cpp-output",
@@ -4690,6 +4693,10 @@ do_spec_1 (spec, inswitch, soft_matched_
 	    this_is_library_file = 1;
 	    break;
 
+	  case 'V':
+	    outfiles[input_file_number] = NULL;
+	    break;
+
 	  case 'w':
 	    this_is_output_file = 1;
 	    break;
@@ -5765,6 +5772,7 @@ main (argc, argv)
   size_t i;
   int value;
   int linker_was_run = 0;
+  int num_linker_inputs = 0;
   char *explicit_link_files;
   char *specs_file;
   const char *p;
@@ -6188,9 +6196,15 @@ main (argc, argv)
 	error_count++;
     }
 
+  /* Determine if there are any linker input files.  */
+  num_linker_inputs = 0;
+  for (i = 0; (int) i < n_infiles; i++)
+    if (explicit_link_files[i] || outfiles[i] != NULL)
+      num_linker_inputs++;
+
   /* Run ld to link all the compiler output files.  */
 
-  if (error_count == 0)
+  if (num_linker_inputs > 0 && error_count == 0)
     {
       int tmp = execution_count;
 
Index: cp/g++spec.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cp/g++spec.c,v
retrieving revision 1.25.12.3
diff -p -u -p -r1.25.12.3 g++spec.c
--- cp/g++spec.c	13 Aug 2002 17:57:36 -0000	1.25.12.3
+++ cp/g++spec.c	18 Aug 2002 00:21:12 -0000
@@ -57,9 +57,11 @@ lang_specific_driver (in_argc, in_argv, 
   /* If non-zero, the user gave us the `-v' flag.  */ 
   int saw_verbose_flag = 0;
 
-  /* This will be 0 if we encounter a situation where we should not
-     link in libstdc++.  */
-  int library = 1;
+  /* This is a tristate:
+     -1 means we should not link in libstdc++
+     0  means we should link in libstdc++ if it is needed
+     1  means libstdc++ is needed and should be linked in.  */
+  int library = 0;
 
   /* The number of arguments being added to what's in argv, other than
      libraries.  We use this to track the number of times we've inserted
@@ -128,10 +130,10 @@ lang_specific_driver (in_argc, in_argv, 
 
       if (argv[i][0] == '-')
 	{
-	  if (library != 0 && (strcmp (argv[i], "-nostdlib") == 0
-			       || strcmp (argv[i], "-nodefaultlibs") == 0))
+	  if (strcmp (argv[i], "-nostdlib") == 0
+	      || strcmp (argv[i], "-nodefaultlibs") == 0)
 	    {
-	      library = 0;
+	      library = -1;
 	    }
 	  else if (strcmp (argv[i], "-lm") == 0
 		   || strcmp (argv[i], "-lmath") == 0
@@ -149,30 +151,37 @@ lang_specific_driver (in_argc, in_argv, 
 	  else if (strcmp (argv[i], "-pg") == 0 || strcmp (argv[i], "-p") == 0)
 	    saw_profile_flag++;
 	  else if (strcmp (argv[i], "-v") == 0)
+	    saw_verbose_flag = 1;
+	  else if (strncmp (argv[i], "-x", 2) == 0)
 	    {
-	      saw_verbose_flag = 1;
-	      if (argc == 2)
+	      if (library == 0)
 		{
-		  /* If they only gave us `-v', don't try to link
-		     in libg++.  */ 
-		  library = 0;
+		  const char * arg;
+		  if (argv[i][2] != '\0')
+		    arg = argv[i]+2;
+		  else if (argv[i+1] != NULL)
+		    arg = argv[i+1];
+		  else  /* Error condition, message will be printed later.  */
+		    arg = "";
+		  if (strcmp (arg, "c++") == 0
+		      || strcmp (arg, "c++-cpp-output") == 0)
+		    library = 1;
 		}
+	      saw_speclang = 1;
 	    }
-	  else if (strncmp (argv[i], "-x", 2) == 0)
-	    saw_speclang = 1;
 	  else if (((argv[i][2] == '\0'
 		     && (char *)strchr ("bBVDUoeTuIYmLiA", argv[i][1]) != NULL)
 		    || strcmp (argv[i], "-Xlinker") == 0
 		    || strcmp (argv[i], "-Tdata") == 0))
 	    quote = argv[i];
-	  else if (library != 0 && ((argv[i][2] == '\0'
-		     && (char *) strchr ("cSEM", argv[i][1]) != NULL)
-		    || strcmp (argv[i], "-MM") == 0
-		    || strcmp (argv[i], "-fsyntax-only") == 0))
+	  else if ((argv[i][2] == '\0'
+		    && (char *) strchr ("cSEM", argv[i][1]) != NULL)
+		   || strcmp (argv[i], "-MM") == 0
+		   || strcmp (argv[i], "-fsyntax-only") == 0)
 	    {
 	      /* Don't specify libraries if we won't link, since that would
 		 cause a warning.  */
-	      library = 0;
+	      library = -1;
 	      added -= 2;
 	    }
 	  else if (strcmp (argv[i], "-static-libgcc") == 0 
@@ -192,16 +201,28 @@ lang_specific_driver (in_argc, in_argv, 
 	      continue;
 	    }
 
-	  /* If the filename ends in .c or .i, put options around it.
+	  /* If the filename ends in .[chi], put options around it.
 	     But not if a specified -x option is currently active.  */
 	  len = strlen (argv[i]);
 	  if (len > 2
-	      && (argv[i][len - 1] == 'c' || argv[i][len - 1] == 'i')
+	      && (argv[i][len - 1] == 'c' 
+		  || argv[i][len - 1] == 'i'
+		  || argv[i][len - 1] == 'h')
 	      && argv[i][len - 2] == '.')
 	    {
 	      args[i] |= LANGSPEC;
 	      added += 2;
 	    }
+	  
+	  /* If we don't know that this is a header file, we might
+	     need to be linking in the libraries.  */
+	  if (library == 0)
+	    {
+	      if ((len <= 2 || strcmp (argv[i] + (len - 2), ".H") != 0)
+		  && (len <= 2 || strcmp (argv[i] + (len - 2), ".h") != 0)
+		  && (len <= 3 || strcmp (argv[i] + (len - 3), ".hh") != 0))
+		library = 1;
+	    }
 	}
     }
 
@@ -209,7 +230,7 @@ lang_specific_driver (in_argc, in_argv, 
     fatal ("argument to `%s' missing\n", quote);
 
   /* If we know we don't have to do anything, bail now.  */
-  if (! added && ! library)
+  if (! added && library <= 0)
     {
       free (args);
       return;
@@ -238,27 +259,37 @@ lang_specific_driver (in_argc, in_argv, 
 
       /* Make sure -lstdc++ is before the math library, since libstdc++
 	 itself uses those math routines.  */
-      if (!saw_math && (args[i] & MATHLIB) && library)
+      if (!saw_math && (args[i] & MATHLIB) && library > 0)
 	{
 	  --j;
 	  saw_math = argv[i];
 	}
 
-      if (!saw_libc && (args[i] & WITHLIBC) && library)
+      if (!saw_libc && (args[i] & WITHLIBC) && library > 0)
 	{
 	  --j;
 	  saw_libc = argv[i];
 	}
 
-      /* Wrap foo.c and foo.i files in a language specification to
+      /* Wrap foo.[chi] files in a language specification to
 	 force the gcc compiler driver to run cc1plus on them.  */
       if (args[i] & LANGSPEC)
 	{
 	  int len = strlen (argv[i]);
-	  if (argv[i][len - 1] == 'i')
-	    arglist[j++] = "-xc++-cpp-output";
-	  else
-	    arglist[j++] = "-xc++";
+	  switch (argv[i][len - 1])
+	    {
+	    case 'c':
+	      arglist[j++] = "-xc++";
+	      break;
+	    case 'i':
+	      arglist[j++] = "-xc++-cpp-output";
+	      break;
+	    case 'h':
+	      arglist[j++] = "-xc++-header";
+	      break;
+	    default:
+	      abort ();
+	    }
 	  arglist[j++] = argv[i];
 	  arglist[j] = "-xnone";
 	}
@@ -268,7 +299,7 @@ lang_specific_driver (in_argc, in_argv, 
     }
 
   /* Add `-lstdc++' if we haven't already done so.  */
-  if (library)
+  if (library > 0)
     {
       arglist[j++] = saw_profile_flag ? LIBSTDCXX_PROFILE : LIBSTDCXX;
       added_libraries++;
@@ -282,7 +313,7 @@ lang_specific_driver (in_argc, in_argv, 
     }
   if (saw_math)
     arglist[j++] = saw_math;
-  else if (library && need_math)
+  else if (library > 0 && need_math)
     {
       arglist[j++] = saw_profile_flag ? MATH_LIBRARY_PROFILE : MATH_LIBRARY;
       added_libraries++;
Index: cp/lang-specs.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cp/lang-specs.h,v
retrieving revision 1.45.14.6
diff -p -u -p -r1.45.14.6 lang-specs.h
--- cp/lang-specs.h	13 Aug 2002 17:57:36 -0000	1.45.14.6
+++ cp/lang-specs.h	18 Aug 2002 00:21:12 -0000
@@ -32,6 +32,21 @@ Boston, MA 02111-1307, USA.  */
   {".cpp", "@c++", 0},
   {".c++", "@c++", 0},
   {".C",   "@c++", 0},
+  {".H",   "@c++-header", 0},
+  {".hh",  "@c++-header", 0},
+  {"@c++-header",
+     /* We should convert -ansi to -std=c++98 even if -fpreprocessed,
+	to get dollars in identifiers correct.  */
+    "%{E|M|MM:cc1plus -E %{!no-gcc:-D__GNUG__=%v1}\
+       %{ansi:-std=c++98} %(cpp_options) %2 %(cpp_debug_options)}\
+     %{!E:%{!M:%{!MM:\
+       %{save-temps:cc1plus -E %{!no-gcc:-D__GNUG__=%v1}\
+		%{ansi:-std=c++98} %(cpp_options) %2 %b.ii \n}\
+      cc1plus %{save-temps:-fpreprocessed %b.ii}\
+	      %{!save-temps:%(cpp_unique_options) %{!no-gcc:-D__GNUG__=%v1}}\
+	%{ansi:-std=c++98} %(cc1_options) %2 %{+e1*}\
+        -o %g.s %{!o*:--output-pch=%i.pch} %W{^o*:--output-pch=%*}%V}}}",
+     CPLUSPLUS_CPP_SPEC},
   {"@c++",
      /* We should convert -ansi to -std=c++98 even if -fpreprocessed,
 	to get dollars in identifiers correct.  */
Index: doc/invoke.texi
===================================================================
RCS file: /cvs/gcc/gcc/gcc/doc/invoke.texi,v
retrieving revision 1.107.2.7
diff -p -u -p -r1.107.2.7 invoke.texi
--- doc/invoke.texi	13 Aug 2002 17:57:42 -0000	1.107.2.7
+++ doc/invoke.texi	18 Aug 2002 00:21:13 -0000
@@ -141,6 +141,7 @@ only one of these two forms, whichever o
 * Code Gen Options::    Specifying conventions for function calls, data layout
                         and register usage.
 * Environment Variables:: Env vars that affect GCC.
+* Precompiled Headers:: Compiling a header once, and using it many times.
 * Running Protoize::    Automatically adding or removing function prototypes.
 @end menu
 
@@ -736,7 +737,7 @@ Objective-C source code.  Note that you 
 Objective-C source code which should not be preprocessed.
 
 @item @var{file}.h
-C header file (not to be compiled or linked).
+C or C++ header file to be turned into a precompiled header.
 
 @item @var{file}.cc
 @itemx @var{file}.cp
@@ -748,6 +749,10 @@ C++ source code which must be preprocess
 the last two letters must both be literally @samp{x}.  Likewise,
 @samp{.C} refers to a literal capital C@.
 
+@item @var{file}.hh
+@itemx @var{file}.H
+C++ header file to be turned into a precompiled header.
+
 @item @var{file}.f
 @itemx @var{file}.for
 @itemx @var{file}.FOR
@@ -811,7 +816,7 @@ name suffix).  This option applies to al
 the next @option{-x} option.  Possible values for @var{language} are:
 @example
 c  c-header  cpp-output
-c++  c++-cpp-output
+c++  c++-header  c++-cpp-output
 objective-c  objc-cpp-output
 assembler  assembler-with-cpp
 ada
@@ -929,22 +934,23 @@ line options for each tool.
 @cindex suffixes for C++ source
 @cindex C++ source file suffixes
 C++ source files conventionally use one of the suffixes @samp{.C},
-@samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx};
-preprocessed C++ files use the suffix @samp{.ii}.  GCC recognizes
-files with these names and compiles them as C++ programs even if you
-call the compiler the same way as for compiling C programs (usually with
-the name @command{gcc}).
+@samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx}; C++
+header files often use @samp{.hh} or @samp{.H}; and preprocessed C++
+files use the suffix @samp{.ii}.  GCC recognizes files with these names
+and compiles them as C++ programs even if you call the compiler the same
+way as for compiling C programs (usually with the name @command{gcc}).
 
 @findex g++
 @findex c++
 However, C++ programs often require class libraries as well as a
 compiler that understands the C++ language---and under some
-circumstances, you might want to compile programs from standard input,
-or otherwise without a suffix that flags them as C++ programs.
-@command{g++} is a program that calls GCC with the default language
-set to C++, and automatically specifies linking against the C++
-library.  On many systems, @command{g++} is also
-installed with the name @command{c++}.
+circumstances, you might want to compile programs or header files from
+standard input, or otherwise without a suffix that flags them as C++
+programs.  You might also like to precompile a C header file with a
+@samp{.h} extension to be used in C++ compilations.  @command{g++} is a
+program that calls GCC with the default language set to C++, and
+automatically specifies linking against the C++ library.  On many
+systems, @command{g++} is also installed with the name @command{c++}.
 
 @cindex invoking @command{g++}
 When you compile C++ programs, you may specify many of the same
@@ -10201,6 +10207,88 @@ preprocessor.
 @include cppenv.texi
 
 @c man end
+
+@node Precompiled Headers
+@section Using Precompiled Headers
+
+Often large projects have many header files that are included in every
+source file.  The time the compiler takes to process these header files
+over and over again can account for nearly all of the time required to
+build the project.  To make builds faster, GCC allows users to
+`precompile' a header file; then, if builds can use the precompiled
+header file they will be much faster.
+
+To create a precompiled header file, simply compile it as you would any
+other file, if necessary using the @option{-x} option to make the driver
+treat it as a C or C++ header file.  You will probably want to use a
+tool like @command{make} to keep the precompiled header up-to-date when
+the headers it contains change.
+
+A precompiled header file will be searched for when @code{#include} is
+seen in the compilation.  As it searches for the included file
+(@pxref{Search Path,,Search Path,cpp.info,The C Preprocessor}) the
+compiler looks for a precompiled header in each directory just before it
+looks for the include file in that directory.  The name searched for is
+the name specified in the @code{#include} with @samp{.pch} appended.  If
+the precompiled header file can't be used, it is ignored.
+
+For instance, if you have @code{#include "all.h"}, and you have
+@file{all.h.pch} in the same directory as @file{all.h}, then the
+precompiled header file will be used if possible, and the original
+header will be used otherwise.
+
+Alternatively, you might decide to put the precompiled header file in a
+directory and use @option{-I} to ensure that directory is searched
+before (or instead of) the directory containing the original header.
+Then, if you want to check that the precompiled header file is always
+used, you can put a file of the same name as the original header in this
+directory containing an @code{#error} command.
+
+This also works with @option{-include}.  So yet another way to use
+precompiled headers is to simply 
+
+There are many other possibilities, limited only by your imagination,
+good sense, and the constraints of your build system.
+
+A precompiled header file can be used only when these conditions apply:
+
+@itemize
+@item
+Only one precompiled header can be used in a particular compilation.
+@item
+A precompiled header can't be used once the first C token is seen.  You
+can have preprocessor directives before a precompiled header; you can
+even include a precompiled header from inside another header, so long as
+there are no C tokens before the @code{#include}.
+@item
+The precompiled header file must be produced for the same language as
+the current compilation.  You can't use a C precompiled header for a C++
+compilation.
+@item
+The precompiled header file must be produced by the same compiler
+version and configuration as the current compilation is using.
+The easiest way to guarantee this is to use the same compiler binary
+for creating and using precompiled headers.
+@item
+Any macros defined before the precompiled header (including with
+@option{-D}) must either be defined in the same way as when the
+precompiled header was generated, or must not affect the precompiled
+header, which usually means that the they don't appear in the
+precompiled header at all.
+@item
+Certain command-line options must be defined in the same way as when the
+precompiled header was generated.  At present, it's not clear which
+options are safe to change and which are not; the safest choice is to
+use exactly the same options when generating and using the precompiled
+header.
+@end itemize
+
+For all of these but the last, the compiler will automatically ignore
+the precompiled header if the conditions aren't met.  For the last item,
+some option changes will cause the precompiled header to be rejected,
+but not all incompatible option combinations have yet been found.  If
+you find a new incompatible combination, please consider filing a bug
+report, see @ref{Bugs}.
 
 @node Running Protoize
 @section Running Protoize
============================================================

Re: [PCH] driver, documentation

[Daniel Jacobowitz]

On Sat, Aug 17, 2002 at 08:32:55PM -0700, Geoffrey Keating wrote:
> 
> This patch starts PCH support.  It adds support in the driver for
> compiling headers, and documents how the PCH support will work.


> +
> +This also works with @option{-include}.  So yet another way to use
> +precompiled headers is to simply 

Lost a sentence here...

Otherwise looks great; it's wonderful to see this coming along.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

Re: [PCH] driver, documentation

[Neil Booth]

Geoffrey Keating wrote:-

> +      break;
> +
> +    case OPT__output_pch:
> +      pch_file = xstrdup (arg + strlen ("--output-pch="));
>        break;

See comment at the top of the file.  Here,

         pch_file = arg;

is enough; arg points to the argument, and it is permanent text.

Neil.

Re: [PCH] driver, documentation

[Neil Booth]

Geoffrey Keating wrote:-

>    {"@c-header",
> -   "%{!E:%ecompilation of header file requested} \
> -    %(trad_capable_cpp) %{ansi:-std=c89} %(cpp_options) %(cpp_debug_options)",
> +   "%{E|M|MM:%(trad_capable_cpp) -lang-c %{ansi:-std=c89} %(cpp_options) \
> +      %(cpp_debug_options)}\
> +    %{!E:cc1 %{ansi:-std=c89} %(cpp_unique_options) %(cc1_options) \
> +     -o %g.s %{!o*:--output-pch=%i.pch} %W{^o*:--output-pch=%*}%V} ",
>     0},

I think "-lang-c" is redundant here.

Neil.

Re: [PCH] driver, documentation

[Joseph S. Myers]

On Sat, 17 Aug 2002, Geoffrey Keating wrote:

> +/* The filename to which we should write a precompiled header, or
> +   NULL if no header will be written in this compile.  */

The GNU Coding Standards say "file name" with a space.

> +     /* We should convert -ansi to -std=c++98 even if -fpreprocessed,
> +	to get dollars in identifiers correct.  */

On the mainline, this conversion is now done in cc1/cc1plus, so you'll
need to make sure the additional -ansi references added here go away in
the next merge from mainline.

> +@node Precompiled Headers
> +@section Using Precompiled Headers
> +

There should be at least one index entry here for precompiled headers.

-- 
Joseph S. Myers
jsm28@cam.ac.uk

Re: [PCH] driver, documentation

[Mike Stump]

On Saturday, August 17, 2002, at 08:32 PM, Geoffrey Keating wrote:
> This patch starts PCH support.  It adds support in the driver for
> compiling headers, and documents how the PCH support will work.


> +A precompiled header file can be used only when these conditions 
> apply:

> +The precompiled header file must be produced for the same language as
> +the current compilation.  You can't use a C precompiled header for a 
> C++
> +compilation.

Hum...  We already solved this problem in our implementation.  Would be 
nice if you mangled the language name into the pch name for 
C/C++/objc/objc++.  I don't think this should be too hard to do, yet, 
it is very useful.

> +Certain command-line options must be defined in the same way as when 
> the
> +precompiled header was generated.  At present, it's not clear which
> +options are safe to change and which are not; the safest choice is to
> +use exactly the same options when generating and using the precompiled
> +header.

Hum, I understand what you mean by this, but this sounds more like an 
internal doc issue.  How about just stating that no other flags or 
environmental concerns should cause a significant generation difference 
and if they do, that would be a bug to be reported.  This way, we set 
up the users expectation, and I think that clearly states the intent 
and be less wishy washy.

I was wondering about flags like -fvolatile, -O2, -O0, -g and 
-ffast-math?  -UMACRO?  Do they rule out pch?  Should they?
I am thinking about C++ where it is possible to have significant 
portions of code for an application in header files.

Re: [PCH] driver, documentation

[Stan Shebs]

Mike Stump wrote:

> I was wondering about flags like -fvolatile, -O2, -O0, -g and 
> -ffast-math?  -UMACRO?  Do they rule out pch?  Should they?
> I am thinking about C++ where it is possible to have significant 
> portions of code for an application in header files.

Ideally, you'd keep around tree rather than RTL, so most backend flags
shouldn't matter.  The most problematic backend flags are the ones that
define cpp macros, so that would include -On because of __OPTIMIZE__
(I think we get this one wrong now).  It would be useful to have some
way of knowing or indicating flags that don't affect a precomp, because
it's too restrictive otherwise - consider a -Wxxx passed only to some
files in a project.

Stan

Re: [PCH] driver, documentation

[Geoff Keating]

> Date: Mon, 19 Aug 2002 10:58:58 -0700
> From: Stan Shebs <shebs@apple.com>

> Mike Stump wrote:
> 
> > I was wondering about flags like -fvolatile, -O2, -O0, -g and 
> > -ffast-math?  -UMACRO?  Do they rule out pch?  Should they?
> > I am thinking about C++ where it is possible to have significant 
> > portions of code for an application in header files.
> 
> Ideally, you'd keep around tree rather than RTL, so most backend flags
> shouldn't matter. 

That would make PCH files slower to use, because RTL would need to be
regenerated (and re-optimised) if it is used.

> The most problematic backend flags are the ones that
> define cpp macros, so that would include -On because of __OPTIMIZE__
> (I think we get this one wrong now).  It would be useful to have some
> way of knowing or indicating flags that don't affect a precomp, because
> it's too restrictive otherwise - consider a -Wxxx passed only to some
> files in a project.

I'm not so worried about cpp macros, I have a complete solution for
that.  I _am_ worried about, for instance, building the header with
-gdwarf-2 and using it with -gstabs; this is a case we'll probably
have to disallow, because there's a tree field that means different
things between the two cases.

The thing is, though, that we _could_ make any flag combination work.
The problem is not the flag combinations that we're thinking about,
the problem is that there are far too many combinations to be able to
test or think about even a small proportion.  

-- 
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>

Re: [PCH] driver, documentation

[Daniel Berlin]

On Mon, 19 Aug 2002, Geoff Keating wrote:

> > Date: Mon, 19 Aug 2002 10:58:58 -0700
> > From: Stan Shebs <shebs@apple.com>
> 
> > Mike Stump wrote:
> > 
> > > I was wondering about flags like -fvolatile, -O2, -O0, -g and 
> > > -ffast-math?  -UMACRO?  Do they rule out pch?  Should they?
> > > I am thinking about C++ where it is possible to have significant 
> > > portions of code for an application in header files.
> > 
> > Ideally, you'd keep around tree rather than RTL, so most backend flags
> > shouldn't matter. 
> 
> That would make PCH files slower to use, because RTL would need to be
> regenerated (and re-optimised) if it is used.

However, it also means we can use PCH as a base mechanism for inter-module 
optimization.

Re: [PCH] driver, documentation

[Neil Booth]

Geoff Keating wrote:-

> I'm not so worried about cpp macros, I have a complete solution for
> that.

What is that?

Neil.

Re: [PCH] driver, documentation

[Jason Merrill]

On Mon, 19 Aug 2002 11:25:31 -0700, Geoff Keating <geoffk@geoffk.org> wrote:

>> Date: Mon, 19 Aug 2002 10:58:58 -0700
>> From: Stan Shebs <shebs@apple.com>
>
>> Mike Stump wrote:
>> 
>> > I was wondering about flags like -fvolatile, -O2, -O0, -g and 
>> > -ffast-math?  -UMACRO?  Do they rule out pch?  Should they?
>> > I am thinking about C++ where it is possible to have significant 
>> > portions of code for an application in header files.
>> 
>> Ideally, you'd keep around tree rather than RTL, so most backend flags
>> shouldn't matter. 
>
> That would make PCH files slower to use, because RTL would need to be
> regenerated (and re-optimised) if it is used.

Why would there be RTL in the PCH?  Nowadays we don't generate RTL until
we're ready to compile down to assembly.

Jason

Re: [PCH] driver, documentation

[Neil Booth]

Stan Shebs wrote:-

> Mike Stump wrote:
> 
> >I was wondering about flags like -fvolatile, -O2, -O0, -g and 
> >-ffast-math?  -UMACRO?  Do they rule out pch?  Should they?
> >I am thinking about C++ where it is possible to have significant 
> >portions of code for an application in header files.
> 
> Ideally, you'd keep around tree rather than RTL, so most backend flags
> shouldn't matter.  The most problematic backend flags are the ones that
> define cpp macros, so that would include -On because of __OPTIMIZE__
> (I think we get this one wrong now).  It would be useful to have some
> way of knowing or indicating flags that don't affect a precomp, because
> it's too restrictive otherwise - consider a -Wxxx passed only to some
> files in a project.

You could do:

1) The set of macros defined in the PCH file after command line
   processing must be a subset of those after the new command line.

2) Any new macro definitions did not have the macro names' identifiers
   in the hash table *at all*.

Since we hash every identifier, this will work, assuming you store the
full hash table in the PCH.  I don't think you can settle for a weaker
set of restrictions, and these are the weakest that are easily
implemented.

Neil.

Re: [PCH] driver, documentation

[Joseph S. Myers]

On Mon, 19 Aug 2002, Stan Shebs wrote:

> (I think we get this one wrong now).  It would be useful to have some
> way of knowing or indicating flags that don't affect a precomp, because
> it's too restrictive otherwise - consider a -Wxxx passed only to some
> files in a project.

Though -W options shouldn't affect precompilation, note that -pedantic can 
certainly affect generated trees (pedantic_non_lvalue etc.) and in some 
obscure cases may change generated code.  (These cases are bugs; the sole 
effect of -pedantic should be to add warnings.)

-- 
Joseph S. Myers
jsm28@cam.ac.uk

Re: [PCH] driver, documentation

[Devang Patel]

On Saturday, August 17, 2002, at 08:32  PM, Geoffrey Keating wrote:

> +@item
> +The precompiled header file must be produced for the same language as
> +the current compilation.  You can't use a C precompiled header for a 
> C++
> +compilation.

> +@item
> +Certain command-line options must be defined in the same way as when 
> the
> +precompiled header was generated.  At present, it's not clear which
> +options are safe to change and which are not; the safest choice is to
> +use exactly the same options when generating and using the precompiled
> +header.
> +@end itemize

Do you want to allow mix & match different flavors of same language, 
c89 vs c99?

-Devang

Re: [PCH] driver, documentation

[Geoff Keating]

> X-Sieve: cmu-sieve 2.0
> Date: Mon, 19 Aug 2002 13:17:20 -0700
> Cc: gcc-patches@gcc.gnu.org
> From: Devang Patel <dpatel@apple.com>
> 
> 
> On Saturday, August 17, 2002, at 08:32  PM, Geoffrey Keating wrote:
> 
> > +@item
> > +The precompiled header file must be produced for the same language as
> > +the current compilation.  You can't use a C precompiled header for a 
> > C++
> > +compilation.
> 
> > +@item
> > +Certain command-line options must be defined in the same way as when 
> > the
> > +precompiled header was generated.  At present, it's not clear which
> > +options are safe to change and which are not; the safest choice is to
> > +use exactly the same options when generating and using the precompiled
> > +header.
> > +@end itemize
> 
> Do you want to allow mix & match different flavors of same language, 
> c89 vs c99?

I wasn't planning to spend time to make this work, but if it works
already I'll be happy.

-- 
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>

Re: [PCH] driver, documentation

[Devang Patel]

On Monday, August 19, 2002, at 02:17  PM, Geoff Keating wrote:

>> X-Sieve: cmu-sieve 2.0
>> Date: Mon, 19 Aug 2002 13:17:20 -0700
>> Cc: gcc-patches@gcc.gnu.org
>> From: Devang Patel <dpatel@apple.com>
>>
>>
>> On Saturday, August 17, 2002, at 08:32  PM, Geoffrey Keating wrote:
>>
>>> +@item
>>> +The precompiled header file must be produced for the same language 
>>> as
>>> +the current compilation.  You can't use a C precompiled header for a
>>> C++
>>> +compilation.
>>
>>> +@item
>>> +Certain command-line options must be defined in the same way as when
>>> the
>>> +precompiled header was generated.  At present, it's not clear which
>>> +options are safe to change and which are not; the safest choice is 
>>> to
>>> +use exactly the same options when generating and using the 
>>> precompiled
>>> +header.
>>> +@end itemize
>>
>> Do you want to allow mix & match different flavors of same language,
>> c89 vs c99?
>
> I wasn't planning to spend time to make this work, but if it works
> already I'll be happy.

It is a good idea, IMO, if we make explicit that it does not work.

-Devang

Re: [PCH] driver, documentation

[Devang Patel]

On Saturday, August 17, 2002, at 08:32  PM, Geoffrey Keating wrote:

> +@item
> +Any macros defined before the precompiled header (including with
> +@option{-D}) must either be defined in the same way as when the
> +precompiled header was generated, or must not affect the precompiled
> +header, which usually means that the they don't appear in the
> +precompiled header at all.

May be it is implicitly said, but how about #undef's ?

Do we want to allow #undef before #include, for macros which are
defined and/or used in precompiled header ?

-Devang

Re: [PCH] driver, documentation

[Geoff Keating]

> X-Sieve: cmu-sieve 2.0
> Date: Mon, 19 Aug 2002 13:19:50 -0700
> Cc: gcc-patches@gcc.gnu.org
> From: Devang Patel <dpatel@apple.com>
> 
> 
> On Saturday, August 17, 2002, at 08:32  PM, Geoffrey Keating wrote:
> 
> > +@item
> > +Any macros defined before the precompiled header (including with
> > +@option{-D}) must either be defined in the same way as when the
> > +precompiled header was generated, or must not affect the precompiled
> > +header, which usually means that the they don't appear in the
> > +precompiled header at all.
> 
> May be it is implicitly said, but how about #undef's ?
> 
> Do we want to allow #undef before #include, for macros which are
> defined and/or used in precompiled header ?

It's implicit.  I guess I could say "Any macros defined (or not
defined)" if that'll make things clearer, any opinions?

-- 
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>

Re: [PCH] driver, documentation

[Devang Patel]

On Monday, August 19, 2002, at 02:17  PM, Geoff Keating wrote:

>> X-Sieve: cmu-sieve 2.0
>> Date: Mon, 19 Aug 2002 13:19:50 -0700
>> Cc: gcc-patches@gcc.gnu.org
>> From: Devang Patel <dpatel@apple.com>
>>
>>
>> On Saturday, August 17, 2002, at 08:32  PM, Geoffrey Keating wrote:
>>
>>> +@item
>>> +Any macros defined before the precompiled header (including with
>>> +@option{-D}) must either be defined in the same way as when the
>>> +precompiled header was generated, or must not affect the precompiled
>>> +header, which usually means that the they don't appear in the
>>> +precompiled header at all.
>>
>> May be it is implicitly said, but how about #undef's ?
>>
>> Do we want to allow #undef before #include, for macros which are
>> defined and/or used in precompiled header ?
>
> It's implicit.  I guess I could say "Any macros defined (or not
> defined)" if that'll make things clearer, any opinions?

Fine with me.

-Devang