On Thu, Jun 22, 2023 at 11:08 AM Prathamesh Kulkarni
<prathamesh.kulka...@linaro.org> wrote:
>
> On Tue, 20 Jun 2023 at 16:47, Richard Biener <richard.guent...@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 ?
Can you retain the case of matching type? Like
(if (types_match (type, TREE_TYPE (@0))
@0
(with
{
tree elem = uniform_vector_p (@0);
}
(if (elem)
{ build_vector_from_val (type, elem); }))))
? Because uniform_vector_p is strictly less powerful than (vec_same_elem_p ...)
OK with that change.
Richard.
>
> 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
