On Tue, Jan 13, 2026 at 6:58 AM Jeffrey Law <[email protected]>
wrote:
>
>
> On 1/9/2026 12:26 PM, Pengxuan Zheng wrote:
> > Implement (X >> C) NE/EQ 0 -> X LT/GE 0 in match.pd instead of
> fold-const.cc.
> >
> > Bootstrapped and tested on x86_64 and aarch64.
> >
> > PR tree-optimization/123109
> >
> > gcc/ChangeLog:
> >
> > * fold-const.cc (fold_binary_loc): Remove (X >> C) NE/EQ 0 -> X
> LT/GE 0
> > folding.
> > * match.pd (`(X >> C) NE/EQ 0 -> X LT/GE 0`): New pattern.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.dg/tree-ssa/vrp99.c: Update test.
> > * gcc.dg/pr123109.c: New test.
> This was submitted prior to stage3->stage4 transition, so if we can get
> resolution on implementation details, it can still go in now.
>
> >
> > +/* Fold (X >> C) != 0 into X < 0 if C is one less than the width
> > + of X. Similarly fold (X >> C) == 0 into X >= 0. */
> > +(for neeq (ne eq)
> > + ltge (lt ge)
> > + (simplify
> > + (neeq
> > + (rshift@2 @0 INTEGER_CST@1)
> > + integer_zerop)
> > + (with { tree itype = signed_type_for (TREE_TYPE (@0)); }
> > + /* Make sure to transform vector compares only to supported
> > + ones or from unsupported ones and check that only after
> > + IPA so offloaded code is handled correctly in this regard. */
> > + (if (wi::to_wide (@1) == element_precision (itype) - 1
> > + && (!VECTOR_TYPE_P (itype)
> > + || (cfun
> > + && cfun->after_inlining
> > + && VECTOR_BOOLEAN_TYPE_P (type)
> > + && (expand_vec_cmp_expr_p (itype, type, ltge)
> > + || !expand_vec_cmp_expr_p (TREE_TYPE (@2),
> > + type, neeq)))))
> > + (ltge (convert:itype @0) { build_zero_cst (itype); })))))
> > +
> So in the PR Richi said the condition ought to be
> canonicalize_math_after_vectorization_p; this seems to check something
> meaningfully different (after_inlining). Can you explain why you ended
> up using the after_inlining test rather than the after_vectorization test?
>
Yes, Jeff, Richard initially suggested to use
canonicalize_math_after_vectorization_p,
but in his latest patch he changed the checks to after_inlining instead
(
https://gcc.gnu.org/cgit/gcc/commit/?id=ae0cdb01b08fb4929ef17c534f86cd9fae78e799
).
Therefore, I updated the checks here to align with Richard's latest
implementation.
Thanks,
Pengxuan
>
> Jeff
>
