Re: [PATCH] tree-optimization/105250 - adjust fold_convertible_p PR105140 fix

[Richard Biener <rguenther@suse.de>]

On Wed, 13 Apr 2022, Richard Biener wrote:

> On Wed, 13 Apr 2022, Richard Sandiford wrote:
> 
> > Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > > The following reverts the original PR105140 fix and goes for instead
> > > applying the additional fold_convert constraint for VECTOR_TYPE
> > > conversions also to fold_convertible_p.  I did not try sanitizing
> > > all of this at this point.
> > >
> > > Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
> > >
> > > 2022-04-13  Richard Biener  <rguenther@suse.de>
> > >
> > > 	PR tree-optimization/105250
> > > 	* fold-const.cc (fold_convertible_p): Revert
> > > 	r12-7979-geaaf77dd85c333, instead check for size equality
> > > 	of the vector types involved.
> > 
> > This doesn't look right, and I think it'll break SVE.  For one
> > thing, the tree_int_cst_equal check is bound to fail for
> > variable-length vectors.
> > 
> > But also, the idea was to allow element-wise conversions between
> > different vector sizes.  For example, you can do a nop/convert
> > from V4SI to V4DI, which converts 4 SIs to 4 DIs.  This is used
> > a lot for conversions to and from “partial” SVE vectors, where smaller
> > elements are stored in wider containers.
> 
> But fold_convertible_p is used as guard for fold_convert in a lot of
> places and that will simply ICE when there's a mismatch in size
> as can be seen in the testcase.  Note the code as before the
> previous fix couldn't really have worked as expected.  Is there any
> testcase that will "break" now?
> 
> I realize the fold_convertible_p comment says "using a NOP_EXPR" which
> means it might conver a narrower set of conversions than fold_convert
> (which will happily use FLOAT_EXPR and friends), but still it should
> allow fold_convert to build the conversion.
> 
> The alternative would have been to emit a NOP_EXPR from fold_convert
> for vector type conversions (with the correct constraints), but then
> not all targets support those, so we'd need a target support check
> in fold_convertible_p then?

Btw, fold_convertible_p is currently used in few places only:

fold-const.cc:fold_convertible_p (const_tree type, const_tree arg)
ipa-cp.cc:      || fold_convertible_p (param_type, value))
ipa-param-manipulation.cc:            if (!fold_convertible_p (TREE_TYPE 
(origin), arg))
ipa-prop.cc:      if (fold_convertible_p (TREE_TYPE (rhs), v->value))
tree-inline.cc:  if (fold_convertible_p (type, value))
tree-inline.cc:      if (fold_convertible_p (caller_type, var))

all in places that try to deal with type mismatches in IPA (from
parameters).

Richard.

> Richard.
> 
> > Thanks,
> > Richard
> > 
> > >
> > > 	* gcc.dg/pr105250.c: New testcase.
> > > ---
> > >  gcc/fold-const.cc               |  7 +++----
> > >  gcc/testsuite/gcc.dg/pr105250.c | 29 +++++++++++++++++++++++++++++
> > >  2 files changed, 32 insertions(+), 4 deletions(-)
> > >  create mode 100644 gcc/testsuite/gcc.dg/pr105250.c
> > >
> > > diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> > > index 7226bc5af01..a57ad0739fb 100644
> > > --- a/gcc/fold-const.cc
> > > +++ b/gcc/fold-const.cc
> > > @@ -2379,13 +2379,12 @@ build_zero_vector (tree type)
> > >    return build_vector_from_val (type, t);
> > >  }
> > >  
> > > -/* Returns true, if ARG, an operand or a type, is convertible to TYPE
> > > -   using a NOP_EXPR.  */
> > > +/* Returns true, if ARG is convertible to TYPE using a NOP_EXPR.  */
> > >  
> > >  bool
> > >  fold_convertible_p (const_tree type, const_tree arg)
> > >  {
> > > -  const_tree orig = TYPE_P (arg) ? arg : TREE_TYPE (arg);
> > > +  const_tree orig = TREE_TYPE (arg);
> > >  
> > >    if (type == orig)
> > >      return true;
> > > @@ -2417,7 +2416,7 @@ fold_convertible_p (const_tree type, const_tree arg)
> > >        return (VECTOR_TYPE_P (orig)
> > >  	      && known_eq (TYPE_VECTOR_SUBPARTS (type),
> > >  			   TYPE_VECTOR_SUBPARTS (orig))
> > > -	      && fold_convertible_p (TREE_TYPE (type), TREE_TYPE (orig)));
> > > +	      && tree_int_cst_equal (TYPE_SIZE (type), TYPE_SIZE (orig)));
> > >  
> > >      default:
> > >        return false;
> > > diff --git a/gcc/testsuite/gcc.dg/pr105250.c b/gcc/testsuite/gcc.dg/pr105250.c
> > > new file mode 100644
> > > index 00000000000..665dd95d8cb
> > > --- /dev/null
> > > +++ b/gcc/testsuite/gcc.dg/pr105250.c
> > > @@ -0,0 +1,29 @@
> > > +/* { dg-do compile } */
> > > +/* { dg-options "-w -Wno-psabi -O2" } */
> > > +
> > > +typedef int __attribute__((__vector_size__(4))) T;
> > > +typedef int __attribute__((__vector_size__(8))) U;
> > > +typedef int __attribute__((__vector_size__(16))) V;
> > > +typedef int __attribute__((__vector_size__(32))) W;
> > > +typedef _Float32 __attribute__((__vector_size__(16))) F;
> > > +typedef _Float64 __attribute__((__vector_size__(32))) G;
> > > +void foo();
> > > +
> > > +foo(int, int, int, int, U, U, V, V, W, W, int,
> > > +     T, int, U, U, V, V, W, W, T,
> > > +     T, int, U, U, V, V, W, W, T,
> > > +     T, int, W, W, T, T, int, int, int,
> > > +     int, int, int, W, int, int, int, int, int, int,
> > > +     V, W, T, int, int, U, F, int, int, int,
> > > +     int, int, int, G)
> > > +{
> > > +  foo(0, 0, 0, 0, (U){}, (U){}, (V){}, (V){}, (W){},
> > > +       (W){}, 2, (T){}, 0, 0, 0, 0, (U){}, (U){},
> > > +       (V){}, (V){}, (W){}, (W){}, (T){},
> > > +       (T){}, 0, 0, 0, 0, (U){}, (U){}, (V){},
> > > +       (V){}, (W){}, (W){}, (T){}, (T){}, 0, 0, 0,
> > > +       0, 0, 0, (T){},
> > > +       (T){}, (W){},
> > > +       (W){}, (T){}, (T){}, 0, 0, 0, 0, 0, 0, (W){},
> > > +       (V){}, (W){}, (T){}, 0, 0, (U){}, (F){});
> > > +}
> > 
> 
> 

-- 
Richard Biener <rguenther@suse.de>
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