Re: [PATCH] Fix PR81354 (rewrite gimple_split_edge)

[Bill Schmidt <wschmidt@linux.vnet.ibm.com>]

> 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.

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 *);