Re: [PATCH] Fix PR81354 (rewrite gimple_split_edge)

[Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>]

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.

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 *);