Re: [stage1][PATCH] Lower VEC_COND_EXPR into internal functions.

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jun 17, 2020 at 10:50 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Mon, Jun 15, 2020 at 2:20 PM Martin Liška <mliska@suse.cz> wrote:
> >
> > On 6/15/20 1:59 PM, Richard Biener wrote:
> > > On Mon, Jun 15, 2020 at 1:19 PM Martin Liška <mliska@suse.cz> wrote:
> > >>
> > >> On 6/15/20 9:14 AM, Richard Biener wrote:
> > >>> On Fri, Jun 12, 2020 at 3:24 PM Martin Liška <mliska@suse.cz> wrote:
> > >>>>
> > >>>> On 6/12/20 11:43 AM, Richard Biener wrote:
> > >>>>> So ... how far are you with enforcing a split VEC_COND_EXPR?
> > >>>>> Thus can we avoid the above completely (even as intermediate
> > >>>>> state)?
> > >>>>
> > >>>> Apparently, I'm quite close. Using the attached patch I see only 2 testsuite
> > >>>> failures:
> > >>>>
> > >>>> FAIL: gcc.dg/tree-ssa/pr68714.c scan-tree-dump-times reassoc1 " <= " 1
> > >>>> FAIL: gcc.target/i386/pr78102.c scan-assembler-times pcmpeqq 3
> > >>>>
> > >>>> The first one is about teaching reassoc about the SSA_NAMEs in VEC_COND_EXPR. I haven't
> > >>>> analyze the second failure.
> > >>>>
> > >>>> I'm also not sure about the gimlification change, I see a superfluous assignments:
> > >>>>      vec_cond_cmp.5 = _1 == _2;
> > >>>>      vec_cond_cmp.6 = vec_cond_cmp.5;
> > >>>>      vec_cond_cmp.7 = vec_cond_cmp.6;
> > >>>>      _3 = VEC_COND_EXPR <vec_cond_cmp.7, { -1, -1, -1, -1, -1, -1, -1, -1 }, { 0, 0, 0, 0, 0, 0, 0, 0 }>;
> > >>>> ?
> > >>>>
> > >>>> So with the suggested patch, the EH should be gone as you suggested. Right?
> > >>>
> > >>> Right, it should be on the comparison already from the start.
> > >>>
> > >>> @@ -14221,9 +14221,13 @@ gimplify_expr (tree *expr_p, gimple_seq
> > >>> *pre_p, gimple_seq *post_p,
> > >>>           case VEC_COND_EXPR:
> > >>>             {
> > >>>               enum gimplify_status r0, r1, r2;
> > >>> -
> > >>>               r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p,
> > >>>                                   post_p, is_gimple_condexpr, fb_rvalue);
> > >>> +           tree xop0 = TREE_OPERAND (*expr_p, 0);
> > >>> +           tmp = create_tmp_var_raw (TREE_TYPE (xop0), "vec_cond_cmp");
> > >>> +           gimple_add_tmp_var (tmp);
> > >>> +           gimplify_assign (tmp, xop0, pre_p);
> > >>> +           TREE_OPERAND (*expr_p, 0) = tmp;
> > >>>               r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p,
> > >>>                                   post_p, is_gimple_val, fb_rvalue);
> > >>>
> > >>> all of VEC_COND_EXPR can now be a simple goto expr_3;
> > >>
> > >> Works for me, thanks!
> > >>
> > >>>
> > >>> diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
> > >>> index 494c9e9c20b..090fb52a2f1 100644
> > >>> --- a/gcc/tree-ssa-forwprop.c
> > >>> +++ b/gcc/tree-ssa-forwprop.c
> > >>> @@ -3136,6 +3136,10 @@ pass_forwprop::execute (function *fun)
> > >>>                       if (code == COND_EXPR
> > >>>                           || code == VEC_COND_EXPR)
> > >>>                         {
> > >>> +                       /* Do not propagate into VEC_COND_EXPRs.  */
> > >>> +                       if (code == VEC_COND_EXPR)
> > >>> +                         break;
> > >>> +
> > >>>
> > >>> err - remove the || code == VEC_COND_EXPR instead?
> > >>
> > >> Yep.
> > >>
> > >>>
> > >>> @@ -2221,24 +2226,12 @@ expand_vector_operations (void)
> > >>>    {
> > >>>      gimple_stmt_iterator gsi;
> > >>>      basic_block bb;
> > >>> -  bool cfg_changed = false;
> > >>>
> > >>>      FOR_EACH_BB_FN (bb, cfun)
> > >>> -    {
> > >>> -      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> > >>> -       {
> > >>> -         expand_vector_operations_1 (&gsi);
> > >>> -         /* ???  If we do not cleanup EH then we will ICE in
> > >>> -            verification.  But in reality we have created wrong-code
> > >>> -            as we did not properly transition EH info and edges to
> > >>> -            the piecewise computations.  */
> > >>> -         if (maybe_clean_eh_stmt (gsi_stmt (gsi))
> > >>> -             && gimple_purge_dead_eh_edges (bb))
> > >>> -           cfg_changed = true;
> > >>> -       }
> > >>> -    }
> > >>>
> > >>> I'm not sure about this.  Consider the C++ testcase where
> > >>> the ?: is replaced by a division.  If veclower needs to replace
> > >>> that with four scalrar division statements then the above
> > >>> still applies - veclower does not correctly duplicate EH info
> > >>> and EH edges to the individual divisions (and we do not know
> > >>> which component might trap).
> > >>>
> > >>> So please leave the above in.  You can try if using integer
> > >>> division makes it break and add such a testcase if there's
> > >>> no coverage for this in the testsuite.
> > >>
> > >> I'm leaving that above. Can you please explain how can a division test-case
> > >> be created?
> > >
> > > typedef long v2di __attribute__((vector_size(16)));
> > >
> > > v2di foo (v2di a, v2di b)
> > > {
> > >    try
> > >    {
> > >      v2di res = a / b;
> > >      return res;
> > >      }
> > >      catch (...)
> > >      {
> > >      return (v2di){};
> > >      }
> > > }
> > >
> > > with -fnon-call-exceptions I see in t.ii.090t.ehdisp (correctly):
> > >
> > > ;;   basic block 2, loop depth 0
> > > ;;    pred:       ENTRY
> > >    [LP 1] _6 = a_4(D) / b_5(D);
> > > ;;    succ:       5
> > > ;;                3
> > >
> > > while after t.ii.226t.veclower we have
> > >
> > > ;;   basic block 2, loop depth 0
> > > ;;    pred:       ENTRY
> > >    _13 = BIT_FIELD_REF <a_4(D), 64, 0>;
> > >    _14 = BIT_FIELD_REF <b_5(D), 64, 0>;
> > >    _15 = _13 / _14;
> > >    _16 = BIT_FIELD_REF <a_4(D), 64, 64>;
> > >    _17 = BIT_FIELD_REF <b_5(D), 64, 64>;
> > >    _18 = _16 / _17;
> > >    _6 = {_15, _18};
> > >    res_7 = _6;
> > >    _8 = res_7;
> > > ;;    succ:       3
> > >
> > > and all EH is gone and we'd ICE if you remove the above hunk.  Hopefully.
> >
> > Yes, it ICEs then:
> >
> >
> > ./xg++ -B. ~/Programming/testcases/ice.c -c -fnon-call-exceptions -O3
> > /home/marxin/Programming/testcases/ice.c: In function ‘v2di foo(v2di, v2di)’:
> > /home/marxin/Programming/testcases/ice.c:3:6: error: statement marked for throw, but doesn’t
> >      3 | v2di foo (v2di a, v2di b)
> >        |      ^~~
> > _6 = {_12, _15};
> > during GIMPLE pass: veclower2
> > /home/marxin/Programming/testcases/ice.c:3:6: internal compiler error: verify_gimple failed
> > 0x10e308a verify_gimple_in_cfg(function*, bool)
> >         /home/marxin/Programming/gcc/gcc/tree-cfg.c:5461
> > 0xfc9caf execute_function_todo
> >         /home/marxin/Programming/gcc/gcc/passes.c:1985
> > 0xfcaafc do_per_function
> >         /home/marxin/Programming/gcc/gcc/passes.c:1640
> > 0xfcaafc execute_todo
> >         /home/marxin/Programming/gcc/gcc/passes.c:2039
> > Please submit a full bug report,
> > with preprocessed source if appropriate.
> > Please include the complete backtrace with any bug report.
> > See <https://gcc.gnu.org/bugs/> for instructions.
> >
> > >
> > > We still generate wrong-code obviously as we'd need to duplicate the
> > > EH info on each component division (and split blocks and generate
> > > extra EH edges).  That's a pre-existing bug of course.  I just wanted
> > > to avoid to create a new instance just because of the early instruction
> > > selection for VEC_COND_EXPR.
> >
> > Fine!
> >
> > >
> > >>>
> > >>> What's missing from the patch is adjusting
> > >>> verify_gimple_assign_ternary from
> > >>>
> > >>>     if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR)
> > >>>          ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1))
> > >>>         || !is_gimple_val (rhs2)
> > >>>         || !is_gimple_val (rhs3))
> > >>>       {
> > >>>         error ("invalid operands in ternary operation");
> > >>>         return true;
> > >>>
> > >>> to the same with the rhs_code == VEC_COND_EXPR case removed.
> > >>
> > >> Hmm. I'm not sure I've got this comment. Why do we want to change it
> > >> and is it done wright in the patch?
> > >
> > > Ah, I missed the hunk you added.
> >
> > That explains the confusion I got.
> >
> > >  But the check should be an inclusive
> > > one, not an exclusive one and earlier accepting a is_gimple_condexpr
> > > is superfluous when you later reject the tcc_comparison part.  Just
> > > testing is_gimple_val is better.  So yes, remove your tree-cfg.c hunk
> > > and just adjust the above test.
> >
> > I simplified that.
> >
> > Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>
> Please double-check the changelog
>
>         (do_store_flag):
>
> +       tree-vect-isel.o \
>
> IMHO we want to move more of the pattern matching magic of RTL
> expansion here to obsolete TER.  So please name it gimple-isel.cc
> (.cc!, not .c)
>
> +  gassign *assign = dyn_cast<gassign *> (SSA_NAME_DEF_STMT (cond));
> +  if (stmt != NULL
> +      && TREE_CODE_CLASS (gimple_assign_rhs_code (assign)) != tcc_comparison)
> +    return ERROR_MARK;
>
> you want stmt == NULL || TREE_CODE_CLASS (...)
>
> in case the def stmt is a call.
>
> +         gimple_seq seq;
> +         tree exp = force_gimple_operand (comb, &seq, true, NULL_TREE);
> +         if (seq)
> +           {
> +             gimple_stmt_iterator gsi = gsi_for_stmt (vcond0);
> +             gsi_insert_before (&gsi, seq, GSI_SAME_STMT);
> +           }
>
> use force_gimple_operand_gsi that makes the above simpler.
>
>           if (invert)
> -           std::swap (*gimple_assign_rhs2_ptr (stmt0),
> -                      *gimple_assign_rhs3_ptr (stmt0));
> -         update_stmt (stmt0);
> +           std::swap (*gimple_assign_rhs2_ptr (vcond0),
> +                      *gimple_assign_rhs3_ptr (vcond0));
>
> use swap_ssa_operands.
>
> +         gimple_assign_set_rhs1 (vcond0, exp);
> +         update_stmt (vcond0);
>
> diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
> index cf2d979fea1..710b17a7c5c 100644
> --- a/gcc/tree-vect-stmts.c
> +++ b/gcc/tree-vect-stmts.c
> @@ -9937,8 +9937,8 @@ vectorizable_condition (vec_info *vinfo,
>         {
>           vec_cond_rhs = vec_oprnds1[i];
>           if (bitop1 == NOP_EXPR)
> -           vec_compare = build2 (cond_code, vec_cmp_type,
> -                                 vec_cond_lhs, vec_cond_rhs);
> +           vec_compare = gimplify_build2 (gsi, cond_code, vec_cmp_type,
> +                                          vec_cond_lhs, vec_cond_rhs);
>           else
>             {
>
> please don't introduce more uses of gimplify_buildN - I'd like to
> get rid of those.  You can use
>
>      gimple_seq stmts = NULL;
>      vec_compare = gimple_build (&stmts, cond_code, ...);
>      gsi_insert_seq_before/after (...);
>
> OK with those changes.

Applying the patch caused

Running target unix//-m32
FAIL: gcc.c-torture/execute/ieee/pr50310.c execution,  -O3
-fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer
-finline-functions
FAIL: gcc.c-torture/execute/ieee/pr50310.c execution,  -O3 -g

and

FAIL: ext/random/simd_fast_mersenne_twister_engine/operators/inequal.cc
(test for excess errors)
UNRESOLVED: ext/random/simd_fast_mersenne_twister_engine/operators/inequal.cc
compilation failed to produce executable

Richard.

> Thanks,
> Richard.
>
>
> > Thanks,
> > Martin
> >
> > >
> > >>>
> > >>> You'll likely figure the vectorizer still creates some VEC_COND_EXPRs
> > >>> with embedded comparisons.
> > >>
> > >> I've fixed 2 failing test-cases I mentioned in the previous email.
> > >>
> > >> Martin
> > >>
> > >>>
> > >>> Thanks,
> > >>> Richard.
> > >>>
> > >>>
> > >>>> Martin
> > >>
> >