Re: [PATCH] Fix PR81354 (rewrite gimple_split_edge)

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Aug 1, 2017 at 5:56 PM, Bill Schmidt
<wschmidt@linux.vnet.ibm.com> wrote:
> On Aug 1, 2017, at 8:50 AM, Bill Schmidt <wschmidt@linux.vnet.ibm.com> wrote:
>>
>> On Aug 1, 2017, at 7:44 AM, Bill Schmidt <wschmidt@linux.vnet.ibm.com> wrote:
>>>
>>>>
>>>> On Aug 1, 2017, at 3:46 AM, Richard Biener <richard.guenther@gmail.com> wrote:
>>>>
>>>> On Mon, Jul 31, 2017 at 4:03 PM, Bill Schmidt
>>>> <wschmidt@linux.vnet.ibm.com> wrote:
>>>>>
>>>>>> On Jul 31, 2017, at 8:19 AM, Bill Schmidt <wschmidt@linux.vnet.ibm.com> wrote:
>>>>>>
>>>>>> That would certainly be much simpler!  I'll regstrap it and test it on the other
>>>>>> occurrence I've found to be certain.
>>>>>
>>>>> Unfortunately, this fails bootstrap:
>>>>>
>>>>> /home/wschmidt/gcc/gcc-mainline-test/gcc/calls.c: In function 'rtx_def* emit_library_call_value_1(int, rtx, rtx, libcall_type, machine_mode, int, va_list)':
>>>>> /home/wschmidt/gcc/gcc-mainline-test/gcc/calls.c:4362:1: error: definition in block 214 does not dominate use in block 14
>>>>> emit_library_call_value_1 (int retval, rtx orgfun, rtx value,
>>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~
>>>>> for SSA_NAME: slsr_772 in statement:
>>>>> slsr_749 = PHI <_17(26), slsr_772(14), slsr_334(214)>
>>>>> PHI argument
>>>>> slsr_772
>>>>> for PHI node
>>>>> slsr_749 = PHI <_17(26), slsr_772(14), slsr_334(214)>
>>>>> during GIMPLE pass: slsr
>>>>> /home/wschmidt/gcc/gcc-mainline-test/gcc/calls.c:4362:1: internal compiler error: verify_ssa failed
>>>>> 0x11567cf3 verify_ssa(bool, bool)
>>>>>      /home/wschmidt/gcc/gcc-mainline-test/gcc/tree-ssa.c:1186
>>>>> 0x10fc3fff execute_function_todo
>>>>>      /home/wschmidt/gcc/gcc-mainline-test/gcc/passes.c:1997
>>>>> 0x10fc277f do_per_function
>>>>>      /home/wschmidt/gcc/gcc-mainline-test/gcc/passes.c:1655
>>>>> 0x10fc42a3 execute_todo
>>>>>      /home/wschmidt/gcc/gcc-mainline-test/gcc/passes.c:2044
>>>>> 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.
>>>>>
>>>>> Not terribly surprising given how sensitive this stuff is.  I can look into why
>>>>> this fails, but looks like it can't be quite this simple, sadly.
>>>>
>>>> Intersting ... a dg-torture.exp run was clean for me (all I
>>>> tested...).  So yes, can you
>>>> check what fails?  Maybe run the testsuite with the stage1 compiler.
>>>
>>> Looks like it's the stage1 that doesn't build.  I think the difference is
>>> that I was building trunk and you were building 6.  I'll try to look into
>>> it later today after I get through some meetings.
>>
>> Sorry, no, it was stage 2 where the failure occurs.
>
> Ah, "good" news.  I believe the bootstrap failure with this change is another
> rediscovery of https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81503, which
> explains why it wasn't seen for GCC 6.  I'll work on getting that fixed and
> then try this again.

Note I very much would like to "fix" split_edge on trunk, on release branches
I'd appreciate if a simpler fix inside SLSR works, like using gsi_insert_on_edge
to avoid splitting edges during the iteration.

Richard.

> Bill
>
>>
>> Bill
>>
>>>
>>> Bill
>>>>
>>>> Richard.
>>>>
>>>>> Bill
>>>>>
>>>>>>
>>>>>> -- Bill
>>>>>>
>>>>>>> On Jul 31, 2017, at 4:15 AM, Richard Biener <richard.guenther@gmail.com> wrote:
>>>>>>>
>>>>>>> On Sun, Jul 30, 2017 at 8:04 PM, Bill Schmidt
>>>>>>> <wschmidt@linux.vnet.ibm.com> wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> PR81354 identifies a latent bug that can happen in SLSR since the
>>>>>>>> conditional candidate support was first added.  SLSR relies on the
>>>>>>>> address of a GIMPLE PHI remaining constant during the course of the
>>>>>>>> optimization pass, but it needs to split edges.  The use of
>>>>>>>> make_single_succ_edge and reinstall_phi_args in gimple_split_edge
>>>>>>>> causes GIMPLE PHI statements to be temporarily expanded to add a
>>>>>>>> predecessor, and then rebuilt to have the original number of
>>>>>>>> predecessors.  The expansion usually, if not always, causes the PHI
>>>>>>>> statement to change address.  Thus gimple_split_edge needs to be
>>>>>>>> rewritten to perform in-situ replacement of PHI arguments.
>>>>>>>>
>>>>>>>> The required pieces of make_single_succ_edge have been extracted into
>>>>>>>> two places:  make_replacement_pred_edge, and some fixup code at the
>>>>>>>> end of gimple_split_edge.  The division is necessary because the
>>>>>>>> destination of the original edge must remember its original
>>>>>>>> predecessors for the switch processing in
>>>>>>>> gimple_redirect_edge_and_branch_1 to work properly.
>>>>>>>>
>>>>>>>> The function gimple_redirect_edge_and_branch was factored into two
>>>>>>>> pieces so that most of it can be used by gimple_split_edge without
>>>>>>>> calling ssa_redirect_edge, which also interferes with PHIs.  The
>>>>>>>> useful bits of ssa_redirect_edge are factored out into the next three
>>>>>>>> lines of gimple_split_edge.
>>>>>>>>
>>>>>>>> Similarly, redirect_eh_edge had already been similarly factored into
>>>>>>>> redirect_eh_edge_1 and ssa_redirect_edge.  I took advantage of that
>>>>>>>> and exposed redirect_eh_edge_1 for use in gimple_redirect_edge_and_branch_1.
>>>>>>>>
>>>>>>>> I've added the test from PR81354 as a torture test, but as we've seen,
>>>>>>>> small changes elsewhere in the optimizer can easily hide the problem.
>>>>>>>>
>>>>>>>> Bootstrapped and tested on powerpc64le-linux-gnu with no regressions.
>>>>>>>> Is this ok for trunk?  Eventually this needs to be backported to GCC 5,
>>>>>>>> 6, and 7 if that's acceptable, since PR81354 was observed on
>>>>>>>> gcc-5-branch.  I haven't yet prepared the backports.
>>>>>>>
>>>>>>> I don't like make_replacement_pred_edge too much.  Wouldn't it work
>>>>>>> to make sure we first shrink and then re-grow like if we simply do the
>>>>>>> redirect_edge_and_branch before the make_single_succ_edge call?
>>>>>>> At least quick testing shows it fixes the testcase on the GCC 6 branch for me.
>>>>>>>
>>>>>>> Index: gcc/tree-cfg.c
>>>>>>> ===================================================================
>>>>>>> --- gcc/tree-cfg.c      (revision 250732)
>>>>>>> +++ gcc/tree-cfg.c      (working copy)
>>>>>>> @@ -2753,12 +2753,16 @@ gimple_split_edge (edge edge_in)
>>>>>>> new_bb = create_empty_bb (after_bb);
>>>>>>> new_bb->frequency = EDGE_FREQUENCY (edge_in);
>>>>>>> new_bb->count = edge_in->count;
>>>>>>> +
>>>>>>> +  /* First redirect the existing edge to avoid reallocating
>>>>>>> +     PHI nodes in dest.  */
>>>>>>> +  e = redirect_edge_and_branch (edge_in, new_bb);
>>>>>>> +  gcc_assert (e == edge_in);
>>>>>>> +
>>>>>>> new_edge = make_edge (new_bb, dest, EDGE_FALLTHRU);
>>>>>>> new_edge->probability = REG_BR_PROB_BASE;
>>>>>>> new_edge->count = edge_in->count;
>>>>>>>
>>>>>>> -  e = redirect_edge_and_branch (edge_in, new_bb);
>>>>>>> -  gcc_assert (e == edge_in);
>>>>>>> reinstall_phi_args (new_edge, e);
>>>>>>>
>>>>>>> return new_bb;
>>>>>>>
>>>>>>> Sorry for misleading you to a complex solution.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Richard.
>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Bill
>>>>>>>>
>>>>>>>>
>>>>>>>> [gcc]
>>>>>>>>
>>>>>>>> 2017-07-30  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
>>>>>>>>
>>>>>>>>    PR tree-optimization/81354
>>>>>>>>    * tree-cfg.c (gimple_redirect_edge_and_branch_1): New decl.
>>>>>>>>    (reinstall_phi_args): Delete function.
>>>>>>>>    (make_replacement_pred_edge): New function.
>>>>>>>>    (gimple_split_edge): Rewrite.
>>>>>>>>    (gimple_redirect_edge_and_branch_1): New function, factored
>>>>>>>>    from...
>>>>>>>>    (gimple_redirect_edge_and_branch): ...here.
>>>>>>>>    (split_critical_edges): Don't re-split already split edges.
>>>>>>>>    * tree-eh.c (redirect_eh_edge_1): Make visible.
>>>>>>>>    * tree-eh.h (redirect_eh_edge_1): Likewise.
>>>>>>>>
>>>>>>>> [gcc/testsuite]
>>>>>>>>
>>>>>>>> 2017-07-30  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
>>>>>>>>
>>>>>>>>    PR tree-optimization/81354
>>>>>>>>    * g++.dg/torture/pr81354.C: New file.
>>>>>>>>
>>>>>>>>
>>>>>>>> Index: gcc/testsuite/g++.dg/torture/pr81354.C
>>>>>>>> ===================================================================
>>>>>>>> --- gcc/testsuite/g++.dg/torture/pr81354.C      (nonexistent)
>>>>>>>> +++ gcc/testsuite/g++.dg/torture/pr81354.C      (working copy)
>>>>>>>> @@ -0,0 +1,24 @@
>>>>>>>> +// PR81354 reported this test as crashing in a limited range of revisions.
>>>>>>>> +// { dg-do compile }
>>>>>>>> +
>>>>>>>> +struct T { double a; double b; };
>>>>>>>> +
>>>>>>>> +void foo(T Ad[], int As[2])
>>>>>>>> +{
>>>>>>>> +  int j;
>>>>>>>> +  int i;
>>>>>>>> +  int Bs[2] = {0,0};
>>>>>>>> +  T Bd[16];
>>>>>>>> +
>>>>>>>> +  for (j = 0; j < 4; j++) {
>>>>>>>> +    for (i = 0; i + 1 <= j + 1; i++) {
>>>>>>>> +      Ad[i + As[0] * j] = Bd[i + Bs[0] * j];
>>>>>>>> +    }
>>>>>>>> +
>>>>>>>> +    i = j + 1;  // <- comment out this line and it does not crash
>>>>>>>> +    for (; i + 1 < 5; i++) {
>>>>>>>> +      Ad[i + As[0] * j].a = 0.0;
>>>>>>>> +      Ad[i + As[0] * j].b = 0.0;
>>>>>>>> +    }
>>>>>>>> +  }
>>>>>>>> +}
>>>>>>>> Index: gcc/tree-cfg.c
>>>>>>>> ===================================================================
>>>>>>>> --- gcc/tree-cfg.c      (revision 250721)
>>>>>>>> +++ gcc/tree-cfg.c      (working copy)
>>>>>>>> @@ -154,6 +154,7 @@ static void make_gimple_switch_edges (gswitch *, b
>>>>>>>> static bool make_goto_expr_edges (basic_block);
>>>>>>>> static void make_gimple_asm_edges (basic_block);
>>>>>>>> static edge gimple_redirect_edge_and_branch (edge, basic_block);
>>>>>>>> +static edge gimple_redirect_edge_and_branch_1 (edge, basic_block);
>>>>>>>> static edge gimple_try_redirect_by_replacing_jump (edge, basic_block);
>>>>>>>>
>>>>>>>> /* Various helpers.  */
>>>>>>>> @@ -2776,35 +2777,6 @@ last_and_only_stmt (basic_block bb)
>>>>>>>> return NULL;
>>>>>>>> }
>>>>>>>>
>>>>>>>> -/* Reinstall those PHI arguments queued in OLD_EDGE to NEW_EDGE.  */
>>>>>>>> -
>>>>>>>> -static void
>>>>>>>> -reinstall_phi_args (edge new_edge, edge old_edge)
>>>>>>>> -{
>>>>>>>> -  edge_var_map *vm;
>>>>>>>> -  int i;
>>>>>>>> -  gphi_iterator phis;
>>>>>>>> -
>>>>>>>> -  vec<edge_var_map> *v = redirect_edge_var_map_vector (old_edge);
>>>>>>>> -  if (!v)
>>>>>>>> -    return;
>>>>>>>> -
>>>>>>>> -  for (i = 0, phis = gsi_start_phis (new_edge->dest);
>>>>>>>> -       v->iterate (i, &vm) && !gsi_end_p (phis);
>>>>>>>> -       i++, gsi_next (&phis))
>>>>>>>> -    {
>>>>>>>> -      gphi *phi = phis.phi ();
>>>>>>>> -      tree result = redirect_edge_var_map_result (vm);
>>>>>>>> -      tree arg = redirect_edge_var_map_def (vm);
>>>>>>>> -
>>>>>>>> -      gcc_assert (result == gimple_phi_result (phi));
>>>>>>>> -
>>>>>>>> -      add_phi_arg (phi, arg, new_edge, redirect_edge_var_map_location (vm));
>>>>>>>> -    }
>>>>>>>> -
>>>>>>>> -  redirect_edge_var_map_clear (old_edge);
>>>>>>>> -}
>>>>>>>> -
>>>>>>>> /* Returns the basic block after which the new basic block created
>>>>>>>> by splitting edge EDGE_IN should be placed.  Tries to keep the new block
>>>>>>>> near its "logical" location.  This is of most help to humans looking
>>>>>>>> @@ -2825,6 +2797,24 @@ split_edge_bb_loc (edge edge_in)
>>>>>>>> return dest_prev;
>>>>>>>> }
>>>>>>>>
>>>>>>>> +/* Create a single-predecessor edge from SRC to DST, replacing the
>>>>>>>> +   predecessor edge E_IN of DST, with flags FLAGS.  This is done in
>>>>>>>> +   situ so that phis in DST will not get re-allocated.  */
>>>>>>>> +
>>>>>>>> +static edge
>>>>>>>> +make_replacement_pred_edge (basic_block src, basic_block dest,
>>>>>>>> +                           edge e_in, int flags)
>>>>>>>> +{
>>>>>>>> +  edge e = ggc_cleared_alloc<edge_def> ();
>>>>>>>> +  n_edges_for_fn (cfun)++;
>>>>>>>> +  e->src = src;
>>>>>>>> +  e->dest = dest;
>>>>>>>> +  e->flags = flags;
>>>>>>>> +  vec_safe_push (src->succs, e);
>>>>>>>> +  e->dest_idx = e_in->dest_idx;
>>>>>>>> +  return e;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> /* Split a (typically critical) edge EDGE_IN.  Return the new block.
>>>>>>>> Abort on abnormal edges.  */
>>>>>>>>
>>>>>>>> @@ -2832,7 +2822,7 @@ static basic_block
>>>>>>>> gimple_split_edge (edge edge_in)
>>>>>>>> {
>>>>>>>> basic_block new_bb, after_bb, dest;
>>>>>>>> -  edge new_edge, e;
>>>>>>>> +  edge e, f;
>>>>>>>>
>>>>>>>> /* Abnormal edges cannot be split.  */
>>>>>>>> gcc_assert (!(edge_in->flags & EDGE_ABNORMAL));
>>>>>>>> @@ -2841,15 +2831,33 @@ gimple_split_edge (edge edge_in)
>>>>>>>>
>>>>>>>> after_bb = split_edge_bb_loc (edge_in);
>>>>>>>>
>>>>>>>> +  /* Create a new block, and an edge F from that block to the original
>>>>>>>> +     destination.  */
>>>>>>>> new_bb = create_empty_bb (after_bb);
>>>>>>>> new_bb->frequency = EDGE_FREQUENCY (edge_in);
>>>>>>>> new_bb->count = edge_in->count;
>>>>>>>> -  new_edge = make_single_succ_edge (new_bb, dest, EDGE_FALLTHRU);
>>>>>>>> +  f = make_replacement_pred_edge (new_bb, dest, edge_in, EDGE_FALLTHRU);
>>>>>>>>
>>>>>>>> -  e = redirect_edge_and_branch (edge_in, new_bb);
>>>>>>>> +  /* Redirect the original edge to its new successor.  */
>>>>>>>> +  e = gimple_redirect_edge_and_branch_1 (edge_in, new_bb);
>>>>>>>> gcc_assert (e == edge_in);
>>>>>>>> -  reinstall_phi_args (new_edge, e);
>>>>>>>> +  e->dest = new_bb;
>>>>>>>> +  vec_safe_push (new_bb->preds, e);
>>>>>>>> +  e->dest_idx = 0;
>>>>>>>>
>>>>>>>> +  /* Fix up the predecessor edge for DEST to now be F.  We can't do
>>>>>>>> +     this prior to gimple_redirect_edge_and_branch_1 without raising
>>>>>>>> +     havoc in the switch code.  */
>>>>>>>> +  int idx = -1;
>>>>>>>> +  for (unsigned int i = 0; i < EDGE_COUNT (dest->preds); i++)
>>>>>>>> +    if (EDGE_PRED (dest, i) == edge_in)
>>>>>>>> +      {
>>>>>>>> +       idx = i;
>>>>>>>> +       break;
>>>>>>>> +      }
>>>>>>>> +  gcc_assert (idx != -1);
>>>>>>>> +  EDGE_PRED (dest, idx) = f;
>>>>>>>> +
>>>>>>>> return new_bb;
>>>>>>>> }
>>>>>>>>
>>>>>>>> @@ -5740,12 +5748,10 @@ gimple_try_redirect_by_replacing_jump (edge e, bas
>>>>>>>> return NULL;
>>>>>>>> }
>>>>>>>>
>>>>>>>> +/* Primary worker for gimple_redirect_edge_and_branch.  */
>>>>>>>>
>>>>>>>> -/* Redirect E to DEST.  Return NULL on failure.  Otherwise, return the
>>>>>>>> -   edge representing the redirected branch.  */
>>>>>>>> -
>>>>>>>> static edge
>>>>>>>> -gimple_redirect_edge_and_branch (edge e, basic_block dest)
>>>>>>>> +gimple_redirect_edge_and_branch_1 (edge e, basic_block dest)
>>>>>>>> {
>>>>>>>> basic_block bb = e->src;
>>>>>>>> gimple_stmt_iterator gsi;
>>>>>>>> @@ -5759,7 +5765,10 @@ static edge
>>>>>>>> return NULL;
>>>>>>>>
>>>>>>>> if (e->flags & EDGE_EH)
>>>>>>>> -    return redirect_eh_edge (e, dest);
>>>>>>>> +    {
>>>>>>>> +      redirect_eh_edge_1 (e, dest, false);
>>>>>>>> +      return e;
>>>>>>>> +    }
>>>>>>>>
>>>>>>>> if (e->src != ENTRY_BLOCK_PTR_FOR_FN (cfun))
>>>>>>>> {
>>>>>>>> @@ -5887,9 +5896,19 @@ static edge
>>>>>>>>   gcc_assert (e->flags & EDGE_FALLTHRU);
>>>>>>>>   break;
>>>>>>>> }
>>>>>>>> +  return e;
>>>>>>>> +}
>>>>>>>>
>>>>>>>> -  /* Update/insert PHI nodes as necessary.  */
>>>>>>>> +/* Redirect E to DEST.  Return NULL on failure.  Otherwise, return the
>>>>>>>> +   edge representing the redirected branch.  */
>>>>>>>>
>>>>>>>> +static edge
>>>>>>>> +gimple_redirect_edge_and_branch (edge e, basic_block dest)
>>>>>>>> +{
>>>>>>>> +  edge f = gimple_redirect_edge_and_branch_1 (e, dest);
>>>>>>>> +  if (f != e)
>>>>>>>> +    return f;
>>>>>>>> +
>>>>>>>> /* Now update the edges in the CFG.  */
>>>>>>>> e = ssa_redirect_edge (e, dest);
>>>>>>>>
>>>>>>>> @@ -8636,13 +8655,18 @@ split_critical_edges (void)
>>>>>>>> basic_block bb;
>>>>>>>> edge e;
>>>>>>>> edge_iterator ei;
>>>>>>>> +  int first_free_block;
>>>>>>>>
>>>>>>>> /* split_edge can redirect edges out of SWITCH_EXPRs, which can get
>>>>>>>>  expensive.  So we want to enable recording of edge to CASE_LABEL_EXPR
>>>>>>>>  mappings around the calls to split_edge.  */
>>>>>>>> start_recording_case_labels ();
>>>>>>>> +  first_free_block = last_basic_block_for_fn (cfun);
>>>>>>>> FOR_ALL_BB_FN (bb, cfun)
>>>>>>>> {
>>>>>>>> +      /* Don't re-split edges we've already split.  */
>>>>>>>> +      if (bb->index >= first_free_block)
>>>>>>>> +       continue;
>>>>>>>>   FOR_EACH_EDGE (e, ei, bb->succs)
>>>>>>>>     {
>>>>>>>>      if (EDGE_CRITICAL_P (e) && !(e->flags & EDGE_ABNORMAL))
>>>>>>>> Index: gcc/tree-eh.c
>>>>>>>> ===================================================================
>>>>>>>> --- gcc/tree-eh.c       (revision 250721)
>>>>>>>> +++ gcc/tree-eh.c       (working copy)
>>>>>>>> @@ -2279,7 +2279,7 @@ make_eh_edges (gimple *stmt)
>>>>>>>> If false, we're being called from generic cfg manipulation code and we
>>>>>>>> should preserve our place within the region tree.  */
>>>>>>>>
>>>>>>>> -static void
>>>>>>>> +void
>>>>>>>> redirect_eh_edge_1 (edge edge_in, basic_block new_bb, bool change_region)
>>>>>>>> {
>>>>>>>> eh_landing_pad old_lp, new_lp;
>>>>>>>> Index: gcc/tree-eh.h
>>>>>>>> ===================================================================
>>>>>>>> --- gcc/tree-eh.h       (revision 250721)
>>>>>>>> +++ gcc/tree-eh.h       (working copy)
>>>>>>>> @@ -32,6 +32,7 @@ extern int lookup_stmt_eh_lp (gimple *);
>>>>>>>> extern bool make_eh_dispatch_edges (geh_dispatch *);
>>>>>>>> extern void make_eh_edges (gimple *);
>>>>>>>> extern edge redirect_eh_edge (edge, basic_block);
>>>>>>>> +extern void redirect_eh_edge_1 (edge, basic_block, bool);
>>>>>>>> extern void redirect_eh_dispatch_edge (geh_dispatch *, edge, basic_block);
>>>>>>>> extern bool operation_could_trap_helper_p (enum tree_code, bool, bool, bool,
>>>>>>>>                                       bool, tree, bool *);
>>
>