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