Bug 194327

For reference, this is the kind of improvement in size we get, by using
-fwhole-program and the ugly #include trick:

   text    data     bss     dec     hex filename
 117428    7832     320  125580   1ea8c jffs2-allinone.o
 122192    9056     328  131576   201f8 fs/jffs2/jffs2.o

We really can't do the #include trick for anything more than testing though --
we need to have --combine working before we can sensibly do this for real.

Alex provided a patch for PR27898 --
http://gcc.gnu.org/ml/gcc-patches/2006-07/msg00187.html

Is this in mainline yet? In our current packages?

Created attachment 134096 [details]
Test case on PowerPC

This is an example of the kind of thing we actually want to do -- build a whole
subdirectory with --combine. Even with Alex's patch for PR27898 it fails in
various ways...

include/asm/paca.h:23: warning: register used for two global register variables

In file included from include/linux/sched.h:51,
		 from fs/jffs2/build.c:16:
include/linux/rbtree.h:139: error: conflicting types for ârb_insert_colorâ
include/linux/rbtree.h:139: error: previous declaration of
ârb_insert_colorâ was here
include/linux/rbtree.h:140: error: conflicting types for ârb_eraseâ
include/linux/rbtree.h:140: error: previous declaration of ârb_eraseâ was
here
include/linux/rbtree.h:143: error: conflicting types for ârb_nextâ
include/linux/rbtree.h:143: error: previous declaration of ârb_nextâ was
here
include/linux/rbtree.h:144: error: conflicting types for ârb_prevâ
include/linux/rbtree.h:144: error: previous declaration of ârb_prevâ was
here
include/linux/rbtree.h:145: error: conflicting types for ârb_firstâ
include/linux/rbtree.h:145: error: previous declaration of ârb_firstâ was
here
include/linux/rbtree.h:146: error: conflicting types for ârb_lastâ
include/linux/rbtree.h:146: error: previous declaration of ârb_lastâ was
here
include/linux/rbtree.h:150: error: conflicting types for ârb_replace_nodeâ
include/linux/rbtree.h:150: error: previous declaration of
ârb_replace_nodeâ was here
include/linux/irq_cpustat.h:20: error: conflicting types for âirq_statâ
include/linux/irq_cpustat.h:20: error: previous declaration of âirq_statâ
was here
include/linux/fs.h:460: error: conflicting types for âmapping_taggedâ
include/linux/fs.h:460: error: previous declaration of âmapping_taggedâ was
here
include/linux/fs.h:993: error: conflicting types for âgeneric_osync_inodeâ
include/linux/fs.h:993: error: previous declaration of
âgeneric_osync_inodeâ was here
 ...

Created attachment 134097 [details]
Test case on i386

Similar test case on i386. Note interesting behaviour when just trying to
combine read.c and write.c:

/opt/crosstool/gcc-4.1.0-glibc-2.3.6/i686-unknown-linux-gnu/bin/i686-unknown-linux-gnu-gcc
-m32  -fno-strict-aliasing -fno-common -Os -fomit-frame-pointer
-fasynchronous-unwind-tables -g -msoft-float -mpreferred-stack-boundary=2  
-mregparm=3 -ffreestanding  -c -o readwrite.o read.i write.i --combine
In file included from include/linux/thread_info.h:22,
		 from include/linux/preempt.h:11,
		 from include/linux/spinlock.h:51,
		 from include/linux/wait.h:26,
		 from include/linux/fs.h:224,
		 from fs/jffs2/write.c:16:
include/asm/thread_info.h:96: warning: register used for two global register
variables
fs/jffs2/write.c:712: internal compiler error: in splice_child_die, at
dwarf2out.c:5492
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.

That may be my self-built cross-compiler though.

Much of what I quoted in comment #3 seems to be explained by GCC PR28706.

If I remove the alignment on struct rb_node from read.i and write.i I can
reproduce the failure mode of comment #4 on my PowerPC native build...

pmac /pmac/git/jffs2-play-2.6/jffs2-combine-ppc $ cc -m64 -fno-strict-aliasing
-fno-common  -Os -fomit-frame-pointer  -msoft-float -pipe -mminimal-toc
-mtraceback=none  -mcall-aixdesc -mtune=power4 -mno-altivec -funit-at-a-time
-mstring -Wa,-maltivec -c -o readwrite.o read.i write.i --combine -Daligned\(x\)=
In file included from include/asm/current.h:16,
                 from include/linux/wait.h:27,
                 from include/linux/fs.h:223,
                 from fs/jffs2/write.c:16:
include/asm/paca.h:23: warning: register used for two global register variables
fs/jffs2/write.c:673: internal compiler error: in splice_child_die, at
dwarf2out.c:5492
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://bugzilla.redhat.com/bugzilla> for instructions.

Removing '-g' from the compiler flags unsurprisingly fixes it.

This is current (4.1.1-1.fc5) Fedora 5 GCC with Alex's patch for PR27898 applied.

Passing every .i file through s/aligned/ignore/g actually makes it work now on
PPC. When combined with -fwhole-program I get object files which are 20% smaller
than the original...

120552    9000     328  129880   1fb58 jffs2-normal.o
106688    7032     304  114024   1bd68 jffs2-combine.o
 97332    5824     304  103460   19424 jffs2-combine-whole-program.o

(Including all files from one and using -fwhole-program was only getting me a 5%
reduction, which seems slightly more reasonable -- and that's still about the
same if I do the same s/aligned/ignore/ and build the same way. I'll have to
test the '--combine -fwhole-program' version once PR28706 is fixed and see if it
actually works.)

The i386 version still has (at least) one problem:
include/asm/processor.h:100: error: conflicting types for 'doublefault_tss'
include/asm/processor.h:100: error: previous declaration of 'doublefault_tss'
was here
include/asm/processor.h:101: error: conflicting types for 'per_cpu__init_tss'
include/asm/processor.h:101: error: previous declaration of 'per_cpu__init_tss'
was here

> The i386 version still has (at least) one problem:
> include/asm/processor.h:100: error: conflicting types for 'doublefault_tss'
> include/asm/processor.h:100: error: previous declaration of 'doublefault_tss'
> was here
> include/asm/processor.h:101: error: conflicting types for 'per_cpu__init_tss'
> include/asm/processor.h:101: error: previous declaration of 'per_cpu__init_tss'
> was here

That's PR27812. 

I've posted a patch for PR287{06,12}.

Perfect, thanks. With your patch and Alex's applied, I can now build modules
with only the 'register used for two global register variables' warnings
(PR27899), which I believe is harmless.

The standard build, for example, of fs/jffs2 on i386 (gcc 4.1.0) gives me this:
  80179     688     176   81043   13c93 fs/jffs2/built-in.o
With -fwhole-program --combine I get this:
  77555     688     188   78431   1325f fs/jffs2/built-in.o

Strangely, that latter result is the same whether I add -funit-at-a-time or
-fno-unit-at-a-time to CFLAGS. 

If you still have issues with rawhide gcc, please reopen.
The global reg warning isn't solved there, but it can be ignored I guess.