On 11/20/23 01:39, Richard Biener wrote:
On Mon, 20 Nov 2023, Jakub Jelinek wrote:
On Mon, Nov 20, 2023 at 07:54:54AM +0000, Richard Biener wrote:
On Fri, 17 Nov 2023, Jakub Jelinek wrote:
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.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Classically this would have been an RTL expansion alternative, given
we want to do less of those the next place would have been the ISEL
pass. Any particular reason you chose widening-mul for this (guess
that pass just has a bad name and it's the effective "optimize" ISEL pass
we have).
I think the ssa-math-opts pass does far more of this staff than the isel
pass which only deals with vector stuff right now and you've even mentioned
that pass for that in the PR90693 thread.
That said, I can move it into the isel pass as well if you prefer that.
I think it's fine as you posted (and Jeff approved), I'm just wondering
if we should rename that pass somehow ;) Note ISEL is more for
required pre-expansion stuff and widen-mul is for expansion related but
optimization parts.
Yea, a rename seems appropriate given how much stuff in there is no
longer math-ops related :-)
jeff
