> Am 31.01.2025 um 10:24 schrieb Jakub Jelinek <ja...@redhat.com>:
>
> Hi!
>
> Since my r15-7223 the niter analysis can recognize one loop during bootstrap
> as being ctz like.
> The patch just turned
> @@ -2173,7 +2173,7 @@ PROC m2pim_NumberIO_BinToStr (CARDINAL x
> _T535_44 = &buf[i.40_2]{lb: 1 sz: 4};
> _T536_45 = x_21 & 1;
> *_T535_44 = _T536_45;
> - _T537_47 = x_21 / 2;
> + _T537_47 = x_21 >> 1;
> x_48 = _T537_47;
> # DEBUG x => x_48
> if (x_48 != 0)
> which is not a big deal for the number_of_iterations_cltz optimization, it
> recognizes both right shift by 1 and unsigned division by 2 (and similarly
> for clz left shift by 1 or multiplication by 2).
> But starting with forwprop1 that change also resulted in
> @@ -1875,9 +1875,9 @@ PROC m2pim_NumberIO_BinToStr (CARDINAL x
> i.40_2 = (INTEGER) _T530_34;
> _T536_45 = x_21 & 1;
> MEM <CARDINAL[1:64]> [(CARDINAL *)&buf][i.40_2]{lb: 1 sz: 4} = _T536_45;
> - _T537_47 = x_21 / 2;
> + _T537_47 = x_21 >> 1;
> # DEBUG x => _T537_47
> - if (x_21 > 1)
> + if (_T537_47 != 0)
> goto <bb 3>; [INV]
> else
> goto <bb 8>; [INV]
> and apparently it is only the latter form that number_of_iterations_cltz
> pattern matches, not the former (after all, that was the exact reason
> for r15-7223).
> The problem is that build_cltz_expr assumes if IFN_C[LT]Z can't be used it
> can use the __builtin_c[lt]z{,l,ll} builtins, and while most of the FEs do
> create them, modula 2 does not.
>
> The following patch just let us punt if the FE doesn't build those builtins.
> I've filed a PR against modula2 so that they add the builtins too.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok
I suppose the middle end could step in for Thors builtins as well, as we do for
memcpy and others.
Richard
> 2025-01-31 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/118689
> PR modula2/115032
> * tree-ssa-loop-niter.cc (build_cltz_expr): Return NULL_TREE if fn is
> NULL and use_ifn is false.
>
> --- gcc/tree-ssa-loop-niter.cc.jj 2025-01-17 11:29:34.080683133 +0100
> +++ gcc/tree-ssa-loop-niter.cc 2025-01-30 14:51:57.528933620 +0100
> @@ -2238,6 +2238,8 @@ build_cltz_expr (tree src, bool leading,
> build_int_cst (integer_type_node, prec));
> }
> }
> + else if (fn == NULL_TREE)
> + return NULL_TREE;
> else if (prec == 2 * lli_prec)
> {
> tree src1 = fold_convert (long_long_unsigned_type_node,
>
> Jakub
>
