A preliminary result of fold_buildN (memory usage included)

[Kazu Hirata]

Hi,

Here is a preliminary result for fold_buildN from my personal tree.  I
compiled cc1-i files with ./cc1 -quiet -O2 -fomit-frame-pointer
-fmem-report -o /dev/null.  I used --enable-gather-detailed-mem-stats
to see how many nodes and bytes we are allocating for trees.  (Thanks
Honza!)  I then summed up the memory usage of trees.

            original       patched   diff%
#nodes    24,234,589    23,577,245 -2.712%
#bytes 1,228,797,315 1,205,528,427 -1.893%

As far as compile time, I consistently see improvements of 0.1% or a
bit more.

In case you are wondering what fold_buildN is,

  fold_build1 (code, type, op0)

is equivalent to

  fold (build (code, type, op0))

except that fold_build1 does not build a scratch node when folding is
successful.  fold_build2 operates in a similar way.

Note that ternary expressions did not take advantage of this
fold_build3 mechanism because of the handling of CALL_EXPR in
fold_ternary.  Since ternary expressions are not as common as binary
expressions, I don't except much difference even after we start using
fold_build3.

Kazu Hirata