Re: [PATCH] Fix PR81354 (rewrite gimple_split_edge)

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

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.

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 *);
>>
>