"H.J. Lu" <hjl.to...@gmail.com> writes: > On Tue, Jul 27, 2021 at 8:31 AM H.J. Lu <hjl.to...@gmail.com> wrote: >> >> On Mon, Jul 26, 2021 at 4:19 PM H.J. Lu <hjl.to...@gmail.com> wrote: >> > >> > On Mon, Jul 26, 2021 at 3:56 PM H.J. Lu <hjl.to...@gmail.com> wrote: >> > > >> > > On Mon, Jul 26, 2021 at 2:53 PM Richard Sandiford >> > > <richard.sandif...@arm.com> wrote: >> > > > >> > > > "H.J. Lu via Gcc-patches" <gcc-patches@gcc.gnu.org> writes: >> > > > > On Mon, Jul 26, 2021 at 11:42 AM Richard Sandiford >> > > > > <richard.sandif...@arm.com> wrote: >> > > > >> >> > > > >> "H.J. Lu via Gcc-patches" <gcc-patches@gcc.gnu.org> writes: >> > > > >> > +to avoid stack realignment when expanding memset. The default is >> > > > >> > +@code{gen_reg_rtx}. >> > > > >> > +@end deftypefn >> > > > >> > + >> > > > >> > @deftypefn {Target Hook} unsigned TARGET_LOOP_UNROLL_ADJUST >> > > > >> > (unsigned @var{nunroll}, class loop *@var{loop}) >> > > > >> > This target hook returns a new value for the number of times >> > > > >> > @var{loop} >> > > > >> > should be unrolled. The parameter @var{nunroll} is the number of >> > > > >> > times >> > > > >> > […] >> > > > >> > @@ -1446,7 +1511,10 @@ can_store_by_pieces (unsigned >> > > > >> > HOST_WIDE_INT len, >> > > > >> > max_size = STORE_MAX_PIECES + 1; >> > > > >> > while (max_size > 1 && l > 0) >> > > > >> > { >> > > > >> > - scalar_int_mode mode = widest_int_mode_for_size >> > > > >> > (max_size); >> > > > >> > + /* Since this can be called before virtual registers are >> > > > >> > ready >> > > > >> > + to use, avoid QI vector mode here. */ >> > > > >> > + fixed_size_mode mode >> > > > >> > + = widest_fixed_size_mode_for_size (max_size, false); >> > > > >> >> > > > >> I think I might have asked this before, sorry, but: when is that >> > > > >> true >> > > > >> and why does it matter? >> > > > > >> > > > > can_store_by_pieces may be called: >> > > > > >> > > > > value-prof.c: if (!can_store_by_pieces (val, >> > > > > builtin_memset_read_str, >> > > > > value-prof.c: if (!can_store_by_pieces (val, >> > > > > builtin_memset_read_str, >> > > > > >> > > > > before virtual registers can be used. When true is passed to >> > > > > widest_fixed_size_mode_for_size, virtual registers may be used >> > > > > to expand memset to broadcast, which leads to ICE. Since for the >> > > > > purpose of can_store_by_pieces, we don't need to expand memset >> > > > > to broadcast and pass false here can avoid ICE. >> > > > >> > > > Ah, I see, thanks. >> > > > >> > > > That sounds like a problem in the way that the memset const function is >> > > > written though. can_store_by_pieces is just a query function, so I >> > > > don't >> > > > think it should be trying to create new registers for >> > > > can_store_by_pieces, >> > > > even if it could. At the same time, can_store_by_pieces should make >> > > > the >> > > > same choices as the real expander would. >> > > > >> > > > I think this means that: >> > > > >> > > > - gen_memset_broadcast should be inlined into its callers, with the >> > > > builtin_memset_read_str getting the CONST_INT_P case and >> > > > builtin_memset_gen_str getting the variable case. >> > > > >> > > > - builtin_memset_read_str should then stop at and return the >> > > > gen_const_vec_duplicate when the prev argument is null. >> > >> > This doesn't work since can_store_by_pieces has >> > >> > cst = (*constfun) (constfundata, nullptr, offset, mode); >> > if (!targetm.legitimate_constant_p (mode, cst)) >> >> We can add a target hook, targetm.legitimate_memset_constant_p, >> which defaults to targetm.legitimate_constant_p. Will it be acceptable? > > In the v5 patch, I changed it to > > cst = (*constfun) (constfundata, nullptr, offset, mode); > /* All CONST_VECTORs are legitimate if vec_duplicate > is supported. */
Maybe “can be loaded” rather than “are legitimate”, since they're not necessarily legitimate in the sense of legitimate_constant_p (hence the patch). Also, since we assume elsewhere that vec_duplicate is a precondition for picking a vector mode, I think we should do the same here (and note that in the comment). So… > if (!((memsetp > && VECTOR_MODE_P (mode) > && GET_MODE_INNER (mode) == QImode > && (optab_handler (vec_duplicate_optab, mode) > != CODE_FOR_nothing)) I think we need only the (memsetp && VECTOR_MODE_P (mode)) check. This feels a bit of a hack TBH. I think the same principles apply to vectors and integers here: forcing the constant to memory is still likely to be an optimisation, but is an extra overhead that we should probably account for. However, I agree this is probably the most practical way forward at the moment. Thanks, Richard > || targetm.legitimate_constant_p (mode, cst))) > return 0; > >> > ix86_legitimate_constant_p only allows 0 or -1 for CONST_VECTOR. >> > can_store_by_pieces doesn't work well for vector modes. >> > >> > > > Only when prev is nonnull should it go on to call the hook >> > > > and copy the constant to the register that the hook returns. >> > > >> > > How about keeping gen_memset_broadcast and passing PREV to it: >> > > >> > > rtx target; >> > > if (CONST_INT_P (data)) >> > > { >> > > rtx const_vec = gen_const_vec_duplicate (mode, data); >> > > if (prev == NULL) >> > > /* Return CONST_VECTOR when called by a query function. */ >> > > target = const_vec; >> > > else >> > > { >> > > /* Use the move expander with CONST_VECTOR. */ >> > > target = targetm.gen_memset_scratch_rtx (mode); >> > > emit_move_insn (target, const_vec); >> > > } >> > > } >> > > else >> > > { >> > > target = targetm.gen_memset_scratch_rtx (mode); >> > > class expand_operand ops[2]; >> > > create_output_operand (&ops[0], target, mode); >> > > create_input_operand (&ops[1], data, QImode); >> > > expand_insn (icode, 2, ops); >> > > if (!rtx_equal_p (target, ops[0].value)) >> > > emit_move_insn (target, ops[0].value); >> > > } >> > > >> > > > I admit that's uglier than the current version, but it looks like >> > > > that's >> > > > what the current interface expects. >> > > > >> > > > Thanks, >> > > > Richard >> > > >> > > >> > > >> > > -- >> > > H.J. >> > >> > >> > >> > -- >> > H.J. >> >> >> >> -- >> H.J.