On Tue, May 7, 2024 at 10:58 AM Stefan Schulze Frielinghaus
<stefa...@linux.ibm.com> wrote:
>
> Ping. Ok for mainline?
OK.
Thanks,
Richard.
> On Thu, Apr 25, 2024 at 09:26:45AM +0200, Stefan Schulze Frielinghaus wrote:
> > Bitcount operations popcount, clz, and ctz are emulated for narrow modes
> > in case an operation is only supported for wider modes. Beside that ctz
> > may be emulated via clz in expand_ctz. Reflect this in
> > expression_expensive_p.
> >
> > I considered the emulation of ctz via clz as not expensive since this
> > basically reduces to ctz (x) = c - (clz (x & ~x)) where c is the mode
> > precision minus 1 which should be faster than a loop.
> >
> > Bootstrapped and regtested on x86_64 and s390. Though, this is probably
> > stage1 material?
> >
> > gcc/ChangeLog:
> >
> > PR tree-optimization/110490
> > * tree-scalar-evolution.cc (expression_expensive_p): Also
> > consider mode widening for popcount, clz, and ctz.
> > ---
> > gcc/tree-scalar-evolution.cc | 23 +++++++++++++++++++++++
> > 1 file changed, 23 insertions(+)
> >
> > diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
> > index b0a5e09a77c..622c7246c1b 100644
> > --- a/gcc/tree-scalar-evolution.cc
> > +++ b/gcc/tree-scalar-evolution.cc
> > @@ -3458,6 +3458,28 @@ bitcount_call:
> > && (optab_handler (optab, word_mode)
> > != CODE_FOR_nothing))
> > break;
> > + /* If popcount is available for a wider mode, we emulate the
> > + operation for a narrow mode by first zero-extending the value
> > + and then computing popcount in the wider mode. Analogue for
> > + ctz. For clz we do the same except that we additionally have
> > + to subtract the difference of the mode precisions from the
> > + result. */
> > + if (is_a <scalar_int_mode> (mode, &int_mode))
> > + {
> > + machine_mode wider_mode_iter;
> > + FOR_EACH_WIDER_MODE (wider_mode_iter, mode)
> > + if (optab_handler (optab, wider_mode_iter)
> > + != CODE_FOR_nothing)
> > + goto check_call_args;
> > + /* Operation ctz may be emulated via clz in expand_ctz. */
> > + if (optab == ctz_optab)
> > + {
> > + FOR_EACH_WIDER_MODE_FROM (wider_mode_iter, mode)
> > + if (optab_handler (clz_optab, wider_mode_iter)
> > + != CODE_FOR_nothing)
> > + goto check_call_args;
> > + }
> > + }
> > return true;
> > }
> > break;
> > @@ -3469,6 +3491,7 @@ bitcount_call:
> > break;
> > }
> >
> > +check_call_args:
> > FOR_EACH_CALL_EXPR_ARG (arg, iter, expr)
> > if (expression_expensive_p (arg, cond_overflow_p, cache, op_cost))
> > return true;
> > --
> > 2.44.0
> >
