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| author | Jakub Jelinek <jakub@redhat.com> | 2023-11-20 10:00:09 +0100 |
|---|---|---|
| committer | Jakub Jelinek <jakub@redhat.com> | 2023-11-20 10:00:09 +0100 |
| commit | d0b6b7f8a6b8115b033441590a6304fb088d193c (patch) | |
| tree | 59a53cfc6bdaae051b44e913d0b6d06b45a19893 /gcc/tree-ssa-threadbackward.cc | |
| parent | 99fad213d5d457162be00d873cd655fe402ca91a (diff) | |
| download | gcc-d0b6b7f8a6b8115b033441590a6304fb088d193c.zip gcc-d0b6b7f8a6b8115b033441590a6304fb088d193c.tar.gz gcc-d0b6b7f8a6b8115b033441590a6304fb088d193c.tar.bz2 | |
tree-ssa-math-opts: popcount (X) == 1 to (X ^ (X - 1)) > (X - 1) optimization [PR90693]
Per the earlier discussions on this PR, the following patch folds
popcount (x) == 1 (and != 1) into (x ^ (x - 1)) > x - 1 (or <=)
if the corresponding popcount optab isn't implemented (I think any
double-word popcount or call will be necessarily slower than the
above cheap 3 op check and even for -Os larger or same size).
I've noticed e.g. C++ aligned new starts with std::has_single_bit
which does popcount (x) == 1.
As a follow-up, I'm considering changing in this routine the popcount
call to IFN_POPCOUNT with 2 arguments and during expansion test costs.
2023-11-20 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/90693
* tree-ssa-math-opts.cc (match_single_bit_test): New function.
(math_opts_dom_walker::after_dom_children): Call it for EQ_EXPR
and NE_EXPR assignments and GIMPLE_CONDs.
* gcc.target/i386/pr90693.c: New test.
Diffstat (limited to 'gcc/tree-ssa-threadbackward.cc')
0 files changed, 0 insertions, 0 deletions