[PATCH] POPCOUNT folding optimizations

[Roger Sayle]

The following patch implements a number of __builtin_popcount related
optimizations.
(i) popcount(x) == 0 can be simplified to x==0, and popcount(x) != 0 to
x!=0.
(ii) popcount(x&1) can be simplified to x&1, and for unsigned x,
popcount(x>>31) to x>>31.
(iii) popcount (x&6) + popcount(y&16) can be simplified to
popcount((x&6)|(y&16))

These may seem obscure transformations, but performing these types of
POPCOUNT
operations are often the performance critical steps in some cheminformatics
applications.

To implement the above transformations I've introduced the tree_nonzero_bits
function,
which is a tree-level version of rtlanal's nonzero_bits used by the RTL
optimizers.

The following patch has been tested on x86_64-pc-linux-gnu with a "make
bootstrap"
and "make check" with no regressions, and passes for the four new gcc.dg
test cases.

Many thanks In advance.  Best regards,

Roger
--
Roger Sayle, PhD.
NextMove Software Limited
Innovation Centre (Unit 23), Cambridge Science Park, Cambridge, CB4 0EY

2018-02-09  Roger Sayle  <roger@nextmovesoftware.com>

        * fold-const.c (tree_nonzero_bits): New function.
        * fold-const.h (tree_nonzero_bits): Likewise.
        * match.pd (POPCOUNT): New patterns to fold BUILTIN_POPCOUNT and
        friends.  POPCOUNT(x&1) => x&1, POPCOUNT(x)==0 => x==0, etc.

2018-02-09  Roger Sayle  <roger@nextmovesoftware.com>

        * gcc.dg/fold-popcount-1.c: New testcase.
        * gcc.dg/fold-popcount-2.c: New testcase.
        * gcc.dg/fold-popcount-3.c: New testcase.
        * gcc.dg/fold-popcount-4.c: New testcase.

-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: fold-popcount-1.c
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20180209/7eae0f1d/attachment.c>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: fold-popcount-2.c
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20180209/7eae0f1d/attachment-0001.c>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: fold-popcount-3.c
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20180209/7eae0f1d/attachment-0002.c>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: fold-popcount-4.c
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20180209/7eae0f1d/attachment-0003.c>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: patch.txt
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20180209/7eae0f1d/attachment.txt>