-fobey-inline (was Re: gcc and inlining)

[Richard Guenther <rguenth at tat dot physik dot uni-tuebingen dot de>]

Hi!

I finally got the patch work for C++ (see attached patch - maybe
completely bogous, though...). An I have some numbers for you:

Without -fobey-inline I get (time per iteration of the bench is displayed)

Benchmark size 32768:
  ET:               4.07126e-08
  Stencil:          3.08246e-08
  ScalarCode (int): 6.23149e-08
  ScalarCode (Loc): 2.04469e-07
Benchmark size 327680:
  ET:               4.3396e-08
  Stencil:          4.61121e-08
  ScalarCode (int): 6.61898e-08
  ScalarCode (Loc): 2.02973e-07
Benchmark size 3276800:
  ET:               4.49557e-08
  Stencil:          4.72165e-08
  ScalarCode (int): 6.81046e-08
  ScalarCode (Loc): 2.11086e-07

Note that for ScalarCode (Loc) which uses Iterator style indexing we are
about one magnitute worse than the rest.

With -fobey-inline the numbers change to:

Benchmark size 32768:
  ET:               4.19604e-08
  Stencil:          3.06718e-08
  ScalarCode (int): 3.93084e-08
  ScalarCode (Loc): 7.59901e-08
Benchmark size 327680:
  ET:               4.29627e-08
  Stencil:          4.6457e-08
  ScalarCode (int): 4.75829e-08
  ScalarCode (Loc): 8.20892e-08
Benchmark size 3276800:
  ET:               4.60333e-08
  Stencil:          4.79431e-08
  ScalarCode (int): 4.73465e-08
  ScalarCode (Loc): 8.29285e-08

Which is now much more reasonable - the optimizers can do useful work on
completely inlined code. (I used -O2 -march=athlon -fomit-frame-pointer
-funroll-loops for the rest of the options)

The patch I used is appended below.

I really would like to have something like this in 3.3!

Thanks, Richard.


Index: gcc/c-objc-common.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-objc-common.c,v
retrieving revision 1.18
diff -u -u -r1.18 c-objc-common.c
--- gcc/c-objc-common.c	25 Oct 2002 17:26:51 -0000	1.18
+++ gcc/c-objc-common.c	12 Mar 2003 21:04:52 -0000
@@ -64,7 +64,7 @@
   if (lookup_attribute ("always_inline", DECL_ATTRIBUTES (fn)) != NULL)
     return 1;

-  return DECL_DECLARED_INLINE_P (fn) && DECL_EXTERNAL (fn);
+  return DECL_DECLARED_INLINE_P (fn) && (DECL_EXTERNAL (fn) || flag_obey_inline);
 }

 static tree
Index: gcc/flags.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/flags.h,v
retrieving revision 1.93
diff -u -u -r1.93 flags.h
--- gcc/flags.h	20 Oct 2002 19:18:29 -0000	1.93
+++ gcc/flags.h	12 Mar 2003 21:04:52 -0000
@@ -384,6 +384,11 @@

 extern int flag_rerun_loop_opt;

+/* Nonzero for -fobey-inline.  If true, the 'inline' keyword must be obeyed,
+   regardless of codesize.  */
+
+extern int flag_obey_inline;
+
 /* Nonzero means make functions that look like good inline candidates
    go inline.  */

Index: gcc/langhooks.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/langhooks.c,v
retrieving revision 1.34.4.1
diff -u -u -r1.34.4.1 langhooks.c
--- gcc/langhooks.c	19 Feb 2003 05:39:28 -0000	1.34.4.1
+++ gcc/langhooks.c	12 Mar 2003 21:04:52 -0000
@@ -300,7 +300,7 @@
   if (lookup_attribute ("always_inline", DECL_ATTRIBUTES (fn)) != NULL)
     return 1;

-  return 0;
+  return flag_obey_inline;
 }

 /* lang_hooks.tree_inlining.add_pending_fn_decls is called before
Index: gcc/toplev.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/toplev.c,v
retrieving revision 1.690.2.12
diff -u -u -r1.690.2.12 toplev.c
--- gcc/toplev.c	10 Mar 2003 12:27:13 -0000	1.690.2.12
+++ gcc/toplev.c	12 Mar 2003 21:04:53 -0000
@@ -663,6 +663,11 @@

 int flag_rerun_loop_opt;

+/* Nonzero for -fobey-inline.  If true, the 'inline' keyword must be obeyed,
+   regardless of codesize.  */
+
+int flag_obey_inline;
+
 /* Nonzero for -finline-functions: ok to inline functions that look like
    good inline candidates.  */

@@ -1031,6 +1036,8 @@
    N_("Generate code for funcs even if they are fully inlined") },
   {"inline", &flag_no_inline, 0,
    N_("Pay attention to the 'inline' keyword") },
+  {"obey-inline", &flag_obey_inline, 1,
+   N_("Obey 'inline' keyword and always inline, regardless of size") },
   {"keep-static-consts", &flag_keep_static_consts, 1,
    N_("Emit static const variables even if they are not used") },
   {"syntax-only", &flag_syntax_only, 1,
Index: gcc/cp/tree.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cp/tree.c,v
retrieving revision 1.307.2.2
diff -u -u -r1.307.2.2 tree.c
--- gcc/cp/tree.c	7 Mar 2003 21:45:29 -0000	1.307.2.2
+++ gcc/cp/tree.c	12 Mar 2003 21:04:55 -0000
@@ -2239,7 +2239,8 @@
   tree fn = *fnp;

   if (flag_really_no_inline
-      && lookup_attribute ("always_inline", DECL_ATTRIBUTES (fn)) == NULL)
+      && (lookup_attribute ("always_inline", DECL_ATTRIBUTES (fn)) == NULL
+          && !(flag_obey_inline && DECL_DECLARED_INLINE_P(fn))))
     return 1;

   /* We can inline a template instantiation only if it's fully
Index: gcc/doc/invoke.texi
===================================================================
RCS file: /cvs/gcc/gcc/gcc/doc/invoke.texi,v
retrieving revision 1.209.2.17
diff -u -u -r1.209.2.17 invoke.texi
--- gcc/doc/invoke.texi	6 Mar 2003 23:35:07 -0000	1.209.2.17
+++ gcc/doc/invoke.texi	12 Mar 2003 21:04:55 -0000
@@ -272,6 +272,7 @@
 -fgcse  -fgcse-lm  -fgcse-sm -floop-optimize -fcrossjumping @gol
 -fif-conversion -fif-conversion2 @gol
 -finline-functions  -finline-limit= at var{n}  -fkeep-inline-functions @gol
+-fobey-inline @gol
 -fkeep-static-consts  -fmerge-constants  -fmerge-all-constants @gol
 -fmove-all-movables  -fnew-ra  -fno-branch-count-reg @gol
 -fno-default-inline  -fno-defer-pop @gol
@@ -3611,6 +3612,12 @@
 is declared @code{static}, nevertheless output a separate run-time
 callable version of the function.  This switch does not affect
 @code{extern inline} functions.
+
+ at item -fobey-inline
+ at opindex fobey-inline
+Make the @code{inline} keyword imperative; inline every function marked
+with the @code{inline} keyword, regardless of size.  Often leads to
+code bloat.

 @item -fkeep-static-consts
 @opindex fkeep-static-consts