[PATCH 0/4] [RFC] Reduce the representation size of optabs

[Richard Henderson]

While adding multiple new optabs over the past week or three, it
occurred to me that (1) there are lots of places to update all in
sync and (2) the representation size of optabs is huge.

The first issue is somewhat trivially accomplished by moving all
optabs knowledge into an optabs.def file.  This could have been
staged differently to prove no errors in the transcription, but
I'm simply going to ask for help reviewing and testing for that.

The second issue is addressed by recognizing that the contents of
the md file, and thus the set of named patterns, does not change
between sub-targets.  The only thing that changes is the value of
HAVE_foo for any pattern foo.

We currently have a very sparse pattern[max_mode] arrays for the
optabs.  Changing that to a dense mapping of known patterns to a
unified pattern array can reduce the dynamic memory requirements
by a factor of 10.  Splitting away the truely unchanging portions
to rodata can reduce the non-sharable data by another factor of 10.

I initially thought of using a minimal perfect hash for the dense
mapping, but gperf turns out to be irritatingly string oriented
and re-implementing a perfect hash algorithm was more than I wanted
to do while I didn't know how much memory I could save.  So at the
moment my "hash function" is a binary search over a table.

Some statistics:

old sizeof(struct target_optabs):
alpha:  225472
ppc64:	396088
i386:   721240

new sizeof(struct target_optabs) + new .rodata
alpha:  210 + 3232
ppc64:	502 + 5568
i386:   1009 + 9624

i386 cc1     old:	new:
.text        9381620	9373204
.rodata      3017472	3031040
.bss         1499552	 778144

I've not yet speed tested this, only completed bootstrap + test
runs for both x86_64 and ppc64.  I've done sanity cross compiles
to alpha and mips (the only SWITCHABLE_TARGET).

I'll be offline til Tuesday, so I won't commit this until then at
least.  Hopefully there will be some good feedback on my return.

FYI, the patchset is available at

  git://repo.or.cz/gcc/rth.git rth/opinit


r~


Richard Henderson (4):
  Introduce and use unknown_optab
  Tidy some include usage + dependencies
  Introduce and use code_to_optab and optab_to_code functions
  Reduce the size of optabs representation

 gcc/Makefile.in          |   35 +-
 gcc/builtins.c           |    2 +-
 gcc/dojump.c             |   13 +-
 gcc/dwarf2out.c          |    1 -
 gcc/genopinit.c          |  932 +++++++++++++++++++++-----------------------
 gcc/ifcvt.c              |    4 +-
 gcc/libfuncs.h           |    3 +-
 gcc/lto-streamer-in.c    |    1 -
 gcc/optabs.c             |  709 +++++++---------------------------
 gcc/optabs.def           |  289 ++++++++++++++
 gcc/optabs.h             |  958 +++++-----------------------------------------
 gcc/rtl.h                |    7 +-
 gcc/tree-vect-generic.c  |   30 +-
 gcc/tree-vect-patterns.c |    2 +-
 gcc/tree-vect-stmts.c    |    2 +-
 15 files changed, 1020 insertions(+), 1968 deletions(-)
 create mode 100644 gcc/optabs.def

-- 
1.7.7.6