https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68786
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For normal vectorized stores, the alignment is preserved through the
MEM_REF/TARGET_MEM_REF type, e.g.
5991 TREE_TYPE (data_ref)
5992 = build_aligned_type (TREE_TYPE (data_ref),
5993 align * BITS_PER_UNIT);
but for masked loads/stores we don't have that available, all we record is
the pointer (what we put as TREE_OPERAND (mem_ref, 0)), which can have
arbitrary type, and the aliasing pointer (with always zero constant).
The alignment info we record through:
set_ptr_info_alignment (get_ptr_info (dataref_ptr), align,
misalign);
Unfortunately, it seems that this way we rely on the optimizers not to lose the
alignment in the points to info, otherwise get_object_alignment_2 assumes the
pointer is fully aligned.
In *.vect it is still preserved:
# PT = nonlocal escaped
# ALIGN = 8, MISALIGN = 0
vectp_pretmp.14_77 = vectp_pretmp.14_74 + 32;
# USE = anything
# CLB = anything
MASK_STORE (vectp_pretmp.14_77, 0B, mask__ifc__37.13_72, vect_cst__73);
but then comes ivopts and turns that into:
_36 = ivtmp.32_7 + 32;
# PT = nonlocal escaped
_37 = (vector(4) double *) _36;
# PT = nonlocal escaped
# ALIGN = 8, MISALIGN = 0
vectp_pretmp.14_77 = _37;
# USE = anything
# CLB = anything
MASK_STORE (vectp_pretmp.14_77, 0B, mask__ifc__37.13_72, vect_cst__73);
and then dom3 turns this into:
_36 = ivtmp.32_7 + 32;
# PT = nonlocal escaped
_37 = (vector(4) double *) _36;
# PT = nonlocal escaped
# ALIGN = 8, MISALIGN = 0
vectp_pretmp.14_77 = _37;
# USE = anything
# CLB = anything
MASK_STORE (_37, 0B, mask__36.12_70, { 1.0e+0, 1.0e+0, 1.0e+0, 1.0e+0 });
and the points to info is there already only on a SSA_NAME that has zero uses.
So, I think that we need to store the original alignment from the vectorization
time somewhere else, so it is not an optimization to have that info preserved.
As the second argument of MASK_{LOAD,STORE} ifn is always 0, and all it matters
is the type on it, perhaps we could stick the alignment in that argument in
there? I.e. call get_object_alignment for the original load/store during
tree-if-conversion.c, in the vectorizer store:
misalign ? misalign & -misalign : align
as INTEGER_CST with the type we were using on the 0 pointer now, and then
during expansion use build_int_cst (TREE_TYPE (gimple_call_arg (stmt, 1)), 0)
instead of gimple_call_arg (stmt, 1), and the actual value use to
build_aligned_type from the rhs type. Richard, are you ok with that
representation?
And then of course is the optimization question, that it is bad that the points
to / alignment info is lost due to what ivopts and following optimization
passes perform. Should we have some late ccp pass that recomputes it, or teach
ivopts to to add alignment/points to info to the stuff it creates, or teach
some optimizations that if they replace one pointer with another defined in the
same bb and the old one has more precise points to info (or similarly for
integers and value ranges) that it could stick that better info onto the other
SSA_NAME?
