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. 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 *);