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?
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
