Re: [PATCH] fold-const: Handle AND, IOR, XOR with stepped vectors [PR112971].

[Richard Biener <rguenther@suse.de>]

On Tue, 19 Dec 2023, Andrew Pinski wrote:

> On Tue, Dec 19, 2023 at 2:40?AM Richard Sandiford
> <richard.sandiford@arm.com> wrote:
> >
> > Richard Biener <rguenther@suse.de> writes:
> > > On Tue, 19 Dec 2023, juzhe.zhong@rivai.ai wrote:
> > >
> > >> Hi, Richard.
> > >>
> > >> After investigating the codes:
> > >> /* Return true if EXPR is the integer constant zero or a complex constant
> > >>    of zero, or a location wrapper for such a constant.  */
> > >>
> > >> bool
> > >> integer_zerop (const_tree expr)
> > >> {
> > >>   STRIP_ANY_LOCATION_WRAPPER (expr);
> > >>
> > >>   switch (TREE_CODE (expr))
> > >>     {
> > >>     case INTEGER_CST:
> > >>       return wi::to_wide (expr) == 0;
> > >>     case COMPLEX_CST:
> > >>       return (integer_zerop (TREE_REALPART (expr))
> > >>               && integer_zerop (TREE_IMAGPART (expr)));
> > >>     case VECTOR_CST:
> > >>       return (VECTOR_CST_NPATTERNS (expr) == 1
> > >>               && VECTOR_CST_DUPLICATE_P (expr)
> > >>               && integer_zerop (VECTOR_CST_ENCODED_ELT (expr, 0)));
> > >>     default:
> > >>       return false;
> > >>     }
> > >> }
> > >>
> > >> I wonder whether we can simplify the codes as follows :?
> > >>       if (integer_zerop (arg1) || integer_zerop (arg2))
> > >>         step_ok_p = (code == BIT_AND_EXPR || code == BIT_IOR_EXPR
> > >>                      || code == BIT_XOR_EXPR);
> > >
> > > Possibly.  I'll let Richard S. comment on the whole structure.
> >
> > The current code is handling cases that require elementwise arithmetic.
> > ISTM that what we're really doing here is identifying cases where
> > whole-vector arithmetic is possible instead.  I think that should be
> > a separate pre-step, rather than integrated into the current code.
> >
> > Largely this would consist of writing out match.pd-style folds in
> > C++ code, so Andrew's fix in comment 7 seems neater to me.
> 
> I didn't like the change to match.pd (even with a comment on why)
> because it violates the whole idea behind canonicalization of
> constants being 2nd operand of commutative and comparison expressions.
> Maybe there are only a few limited match/simplify patterns which need
> to add the :c for constants not being the 2nd operand but there needs
> to be a comment on why :c is needed for this.

Agreed.  Note that in theory we of course could define extra
canonicalization rules for CST op CST in tree_swap_operands_p,
there are some cases those surivive, mostly around FP and
dynamic rounding state.  I'd rather go that route if we decide
that match.pd should catch this.

> >
> > But if this must happen in const_binop instead, then we could have
> > a function like:
> 
> The reasoning of why it should be in const_binop rather than in match
> is because both operands are constants.

+1

Richard.

> Now for commutative expressions, we only need to check the first
> operand for zero/all_ones and try again swapping the operands. This
> will most likely solve the problem of writing so much code.
> We could even use lambdas to simplify things too.
> 
> Thanks,
> Andrew Pinski
> 
> >
> > /* OP is the INDEXth operand to CODE (counting from zero) and OTHER_OP
> >    is the other operand.  Try to use the value of OP to simplify the
> >    operation in one step, without having to process individual elements.  */
> > tree
> > simplify_const_binop (tree_code code, rtx op, rtx other_op, int index)
> > {
> >   ...
> > }
> >
> > Thanks,
> > Richard
> >
> > >
> > > Richard.
> > >
> > >>
> > >>
> > >>
> > >> juzhe.zhong@rivai.ai
> > >>
> > >> From: Richard Biener
> > >> Date: 2023-12-19 17:12
> > >> To: juzhe.zhong@rivai.ai
> > >> CC: Robin Dapp; gcc-patches; pan2.li; richard.sandiford; Richard Biener; pinskia
> > >> Subject: Re: Re: [PATCH] fold-const: Handle AND, IOR, XOR with stepped vectors [PR112971].
> > >> On Tue, 19 Dec 2023, juzhe.zhong@rivai.ai wrote:
> > >>
> > >> > Hi?Richard. Do you mean add the check as follows ?
> > >> >
> > >> >       if (VECTOR_CST_NELTS_PER_PATTERN (arg1) == 1
> > >> >           && VECTOR_CST_NELTS_PER_PATTERN (arg2) == 3
> > >>
> > >> Or <= 3 which would allow combining.  As said, not sure what
> > >> == 2 would be and whether that would work.
> > >>
> > >> Btw, integer_allonesp should also allow to be optimized for
> > >> and/ior at least.  Possibly IOR/AND with the sign bit for
> > >> signed elements as well.
> > >>
> > >> I wonder if there's a programmatic way to identify OK cases
> > >> rather than enumerating them.
> > >>
> > >> >           && integer_zerop (VECTOR_CST_ELT (arg1, 0)))
> > >> >         step_ok_p = (code == BIT_AND_EXPR || code == BIT_IOR_EXPR
> > >> >           || code == BIT_XOR_EXPR);
> > >> >       else if (VECTOR_CST_NELTS_PER_PATTERN (arg2) == 1
> > >> >           && VECTOR_CST_NELTS_PER_PATTERN (arg1) == 3
> > >> >           && integer_zerop (VECTOR_CST_ELT (arg2, 0)))
> > >> >         step_ok_p = (code == BIT_AND_EXPR || code == BIT_IOR_EXPR
> > >> >           || code == BIT_XOR_EXPR);
> > >> >
> > >> >
> > >> >
> > >> > juzhe.zhong@rivai.ai
> > >> >
> > >> > From: Richard Biener
> > >> > Date: 2023-12-19 16:15
> > >> > To: ???
> > >> > CC: rdapp.gcc; gcc-patches; pan2.li; richard.sandiford; richard.guenther; Andrew Pinski
> > >> > Subject: Re: [PATCH] fold-const: Handle AND, IOR, XOR with stepped vectors [PR112971].
> > >> > On Tue, 19 Dec 2023, ??? wrote:
> > >> >
> > >> > > Thanks Robin send initial patch to fix this ICE bug.
> > >> > >
> > >> > > CC to Richard S, Richard B, and Andrew.
> > >> >
> > >> > Just one comment, it seems that VECTOR_CST_STEPPED_P should
> > >> > implicitly include VECTOR_CST_DUPLICATE_P since it would be
> > >> > a step of zero (but as implemented it doesn't catch this).
> > >> > Looking at the implementation it's odd that we can handle
> > >> > VECTOR_CST_NELTS_PER_PATTERN == 1 (duplicate) and
> > >> > == 3 (stepped) but not == 2 (not sure what that would be).
> > >> >
> > >> > Maybe the tests can be re-formulated in terms of
> > >> > VECTOR_CST_NELTS_PER_PATTERN?
> > >> >
> > >> > Richard.
> > >> >
> > >> > > Thanks.
> > >> > >
> > >> > >
> > >> > >
> > >> > > juzhe.zhong@rivai.ai
> > >> > >
> > >> > > From: Robin Dapp
> > >> > > Date: 2023-12-19 03:50
> > >> > > To: gcc-patches
> > >> > > CC: rdapp.gcc; Li, Pan2; juzhe.zhong@rivai.ai
> > >> > > Subject: [PATCH] fold-const: Handle AND, IOR, XOR with stepped vectors [PR112971].
> > >> > > Hi,
> > >> > >
> > >> > > found in PR112971, this patch adds folding support for bitwise operations
> > >> > > of const duplicate zero vectors and stepped vectors.
> > >> > > On riscv we have the situation that a folding would perpetually continue
> > >> > > without simplifying because e.g. {0, 0, 0, ...} & {7, 6, 5, ...} would
> > >> > > not fold to {0, 0, 0, ...}.
> > >> > >
> > >> > > Bootstrapped and regtested on x86 and aarch64, regtested on riscv.
> > >> > >
> > >> > > I won't be available to respond quickly until next year.  Pan or Juzhe,
> > >> > > as discussed, feel free to continue with possible revisions.
> > >> > >
> > >> > > Regards
> > >> > > Robin
> > >> > >
> > >> > >
> > >> > > gcc/ChangeLog:
> > >> > >
> > >> > > PR middle-end/112971
> > >> > >
> > >> > > * fold-const.cc (const_binop): Handle
> > >> > > zerop@1  AND/IOR/XOR  VECT_CST_STEPPED_P@2
> > >> > >
> > >> > > gcc/testsuite/ChangeLog:
> > >> > >
> > >> > > * gcc.target/riscv/rvv/autovec/pr112971.c: New test.
> > >> > > ---
> > >> > > gcc/fold-const.cc                              | 14 +++++++++++++-
> > >> > > .../gcc.target/riscv/rvv/autovec/pr112971.c    | 18 ++++++++++++++++++
> > >> > > 2 files changed, 31 insertions(+), 1 deletion(-)
> > >> > > create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
> > >> > >
> > >> > > diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> > >> > > index f5d68ac323a..43ed097bf5c 100644
> > >> > > --- a/gcc/fold-const.cc
> > >> > > +++ b/gcc/fold-const.cc
> > >> > > @@ -1653,8 +1653,20 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
> > >> > >      {
> > >> > >        tree type = TREE_TYPE (arg1);
> > >> > >        bool step_ok_p;
> > >> > > +
> > >> > > +      /* AND, IOR as well as XOR with a zerop can be handled directly.  */
> > >> > >        if (VECTOR_CST_STEPPED_P (arg1)
> > >> > > -   && VECTOR_CST_STEPPED_P (arg2))
> > >> > > +   && VECTOR_CST_DUPLICATE_P (arg2)
> > >> > > +   && integer_zerop (VECTOR_CST_ELT (arg2, 0)))
> > >> > > + step_ok_p = code == BIT_AND_EXPR || code == BIT_IOR_EXPR
> > >> > > +   || code == BIT_XOR_EXPR;
> > >> > > +      else if (VECTOR_CST_STEPPED_P (arg2)
> > >> > > +        && VECTOR_CST_DUPLICATE_P (arg1)
> > >> > > +        && integer_zerop (VECTOR_CST_ELT (arg1, 0)))
> > >> > > + step_ok_p = code == BIT_AND_EXPR || code == BIT_IOR_EXPR
> > >> > > +   || code == BIT_XOR_EXPR;
> > >> > > +      else if (VECTOR_CST_STEPPED_P (arg1)
> > >> > > +        && VECTOR_CST_STEPPED_P (arg2))
> > >> > > /* We can operate directly on the encoding if:
> > >> > >       a3 - a2 == a2 - a1 && b3 - b2 == b2 - b1
> > >> > > diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
> > >> > > new file mode 100644
> > >> > > index 00000000000..816ebd3c493
> > >> > > --- /dev/null
> > >> > > +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
> > >> > > @@ -0,0 +1,18 @@
> > >> > > +/* { dg-do compile }  */
> > >> > > +/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3 -fno-vect-cost-model" }  */
> > >> > > +
> > >> > > +int a;
> > >> > > +short b[9];
> > >> > > +char c, d;
> > >> > > +void e() {
> > >> > > +  d = 0;
> > >> > > +  for (;; d++) {
> > >> > > +    if (b[d])
> > >> > > +      break;
> > >> > > +    a = 8;
> > >> > > +    for (; a >= 0; a--) {
> > >> > > +      char *f = &c;
> > >> > > +      *f &= d == (a & d);
> > >> > > +    }
> > >> > > +  }
> > >> > > +}
> > >> > >
> > >> >
> > >> >
> > >>
> > >>
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)