Re: [RFC][PR82479] missing popcount builtin detection

[Richard Biener <richard dot guenther at gmail dot com>]

On Wed, Jan 24, 2018 at 10:56 PM, Kugan Vivekanandarajah
<kugan.vivekanandarajah@linaro.org> wrote:
> Hi All,
>
> Here is a patch for popcount builtin detection similar to LLVM. I
> would like to queue this for review for next stage 1.
>
> 1. This is done part of loop-distribution and effective for -O3 and above.
> 2. This does not distribute loop to detect popcount (like
> memcpy/memmove). I dont think that happens in practice. Please correct
> me if I am wrong.

But then it has no business inside loop distribution but instead is
doing final value
replacement, right?  You are pattern-matching the whole loop after all.  I think
final value replacement would already do the correct thing if you
teached number of
iteration analysis that niter for

  <bb 3> [local count: 955630224]:
  # b_11 = PHI <b_5(5), b_8(6)>
  _1 = b_11 + -1;
  b_8 = _1 & b_11;
  if (b_8 != 0)
    goto <bb 6>; [89.00%]
  else
    goto <bb 8>; [11.00%]

  <bb 6> [local count: 850510900]:
  goto <bb 3>; [100.00%]

is related to popcount (b_5).

Richard.

> Bootstrapped and regression tested on aarch64-linux-gnu with no new regressions.
>
> Thanks,
> Kugan
>
> gcc/ChangeLog:
>
> 2018-01-25  Kugan Vivekanandarajah  <kuganv@linaro.org>
>
>     PR middle-end/82479
>     * tree-loop-distribution.c (handle_popcount): New.
>     (pass_loop_distribution::execute): Use handle_popcount.
>
> gcc/testsuite/ChangeLog:
>
> 2018-01-25  Kugan Vivekanandarajah  <kuganv@linaro.org>
>
>     PR middle-end/82479
>     * gcc.dg/tree-ssa/popcount.c: New test.