On Tue, 20 Jun 2023 at 16:47, Richard Biener <richard.guenther@gmail.com> wrote:
>
> On Tue, Jun 20, 2023 at 11:56 AM Prathamesh Kulkarni via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > Hi Richard,
> > For the following reduced test-case taken from PR:
> >
> > #include "arm_sve.h"
> > svuint32_t l() {
> >   alignas(16) const unsigned int lanes[4] = {0, 0, 0, 0};
> >   return svld1rq_u32(svptrue_b8(), lanes);
> > }
> >
> > compiling with -O3 -mcpu=generic+sve results in following ICE:
> > during GIMPLE pass: fre
> > pr110280.c: In function 'l':
> > pr110280.c:5:1: internal compiler error: in eliminate_stmt, at
> > tree-ssa-sccvn.cc:6890
> >     5 | }
> >       | ^
> > 0x865fb1 eliminate_dom_walker::eliminate_stmt(basic_block_def*,
> > gimple_stmt_iterator*)
> >         ../../gcc/gcc/tree-ssa-sccvn.cc:6890
> > 0x120bf4d eliminate_dom_walker::before_dom_children(basic_block_def*)
> >         ../../gcc/gcc/tree-ssa-sccvn.cc:7324
> > 0x120bf4d eliminate_dom_walker::before_dom_children(basic_block_def*)
> >         ../../gcc/gcc/tree-ssa-sccvn.cc:7257
> > 0x1aeec77 dom_walker::walk(basic_block_def*)
> >         ../../gcc/gcc/domwalk.cc:311
> > 0x11fd924 eliminate_with_rpo_vn(bitmap_head*)
> >         ../../gcc/gcc/tree-ssa-sccvn.cc:7504
> > 0x1214664 do_rpo_vn_1
> >         ../../gcc/gcc/tree-ssa-sccvn.cc:8616
> > 0x1215ba5 execute
> >         ../../gcc/gcc/tree-ssa-sccvn.cc:8702
> >
> > cc1 simplifies:
> >   lanes[0] = 0;
> >   lanes[1] = 0;
> >   lanes[2] = 0;
> >   lanes[3] = 0;
> >   _1 = { -1, ... };
> >   _7 = svld1rq_u32 (_1, &lanes);
> >
> > to:
> >   _9 = MEM <vector(4) unsigned int> [(unsigned int * {ref-all})&lanes];
> >   _7 = VEC_PERM_EXPR <_9, _9, { 0, 1, 2, 3, ... }>;
> >
> > and then fre1 dump shows:
> > Applying pattern match.pd:8675, generic-match-5.cc:9025
> > Match-and-simplified VEC_PERM_EXPR <_9, _9, { 0, 1, 2, 3, ... }> to {
> > 0, 0, 0, 0 }
> > RHS VEC_PERM_EXPR <_9, _9, { 0, 1, 2, 3, ... }> simplified to { 0, 0, 0, 0 }
> >
> > The issue seems to be with the following pattern:
> > (simplify
> >  (vec_perm vec_same_elem_p@0 @0 @1)
> >  @0)
> >
> > which simplifies above VEC_PERM_EXPR to:
> > _7 = {0, 0, 0, 0}
> > which is incorrect since _9 and mask have different vector lengths.
> >
> > The attached patch amends the pattern to simplify above VEC_PERM_EXPR
> > only if operand and mask have same number of elements, which seems to fix
> > the issue, and we're left with the following in .optimized dump:
> >   <bb 2> [local count: 1073741824]:
> >   _2 = VEC_PERM_EXPR <{ 0, 0, 0, 0 }, { 0, 0, 0, 0 }, { 0, 1, 2, 3, ... }>;
>
> it would be nice to have this optimized.
>
> -
>  (simplify
>   (vec_perm vec_same_elem_p@0 @0 @1)
> - @0)
> + (if (known_eq (TYPE_VECTOR_SUBPARTS (TREE_TYPE (@0)),
> +               TYPE_VECTOR_SUBPARTS (TREE_TYPE (@1))))
> +  @0))
>
> that looks good I think.  Maybe even better use 'type' instead of TREE_TYPE (@1)
> since that's more obviously the return type in which case
>
>   (if (types_match (type, TREE_TYPE (@0))
>
> would be more to the point.
>
> But can't you to simplify this in the !known_eq case do a simple
>
>   { build_vector_from_val (type, the-element); }
>
> ?  The 'vec_same_elem_p' predicate doesn't get you at the element,
>
>  (with { tree el = uniform_vector_p (@0); }
>   (if (el)
>    { build_vector_from_val (type, el); })))
>
> would be the cheapest workaround.
Hi Richard,
Thanks for the suggestions. Using build_vector_from_val simplifies it to:
  <bb 2> [local count: 1073741824]:
  return { 0, ... };

Patch is bootstrapped+tested on aarch64-linux-gnu, in progress on
x86_64-linux-gnu.
OK to commit ?

Thanks,
Prathamesh
>
> >   return _2;
> >
> > code-gen:
> > l:
> >         mov     z0.b, #0
> >         ret
> >
> > Patch is bootstrapped+tested on aarch64-linux-gnu.
> > OK to commit ?
> >
> > Thanks,
> > Prathamesh