On Sun, Jul 30, 2017 at 8:04 PM, Bill Schmidt
<wschm...@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 <wschm...@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 <wschm...@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 *);
>
