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tree-optimization/97199 - fix virtual operand update in if-conversion

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This fixes a corner case with virtual operand update in if-conversion
by re-organizing the code to remove edges only after the last point
we need virtual PHI operands to be available.

2020-09-25  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/97199
	* tree-if-conv.c (combine_blocks): Remove edges only
	after looking at virtual PHI args.
This commit is contained in:
Richard Biener 2020-09-25 13:08:48 +02:00
parent 8c775bf447
commit 4dcc7f03b5
1 changed files with 63 additions and 44 deletions
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107
gcc/tree-if-conv.c
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@ -2544,8 +2544,7 @@ combine_blocks (class loop *loop)
if (need_to_predicate)
predicate_statements (loop);
/* Merge basic blocks: first remove all the edges in the loop,
except for those from the exit block. */
/* Merge basic blocks. */
exit_bb = NULL;
bool *predicated = XNEWVEC (bool, orig_loop_num_nodes);
for (i = 0; i < orig_loop_num_nodes; i++)
@ -2561,43 +2560,6 @@ combine_blocks (class loop *loop)
}
gcc_assert (exit_bb != loop->latch);
for (i = 1; i < orig_loop_num_nodes; i++)
{
bb = ifc_bbs[i];
for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei));)
{
if (e->src == exit_bb)
ei_next (&ei);
else
remove_edge (e);
}
}
if (exit_bb != NULL)
{
if (exit_bb != loop->header)
{
/* Connect this node to loop header. */
make_single_succ_edge (loop->header, exit_bb, EDGE_FALLTHRU);
set_immediate_dominator (CDI_DOMINATORS, exit_bb, loop->header);
}
/* Redirect non-exit edges to loop->latch. */
FOR_EACH_EDGE (e, ei, exit_bb->succs)
{
if (!loop_exit_edge_p (loop, e))
redirect_edge_and_branch (e, loop->latch);
}
set_immediate_dominator (CDI_DOMINATORS, loop->latch, exit_bb);
}
else
{
/* If the loop does not have an exit, reconnect header and latch. */
make_edge (loop->header, loop->latch, EDGE_FALLTHRU);
set_immediate_dominator (CDI_DOMINATORS, loop->latch, loop->header);
}
merge_target_bb = loop->header;
/* Get at the virtual def valid for uses starting at the first block
@ -2682,13 +2644,9 @@ combine_blocks (class loop *loop)
last = gsi_last_bb (merge_target_bb);
gsi_insert_seq_after_without_update (&last, bb_seq (bb), GSI_NEW_STMT);
set_bb_seq (bb, NULL);
delete_basic_block (bb);
}
/* If possible, merge loop header to the block with the exit edge.
This reduces the number of basic blocks to two, to please the
vectorizer that handles only loops with two nodes. */
/* Fixup virtual operands in the exit block. */
if (exit_bb
&& exit_bb != loop->header)
{
@ -2698,6 +2656,11 @@ combine_blocks (class loop *loop)
vphi = get_virtual_phi (exit_bb);
if (vphi)
{
/* When there's just loads inside the loop a stray virtual
PHI merging the uses can appear, update last_vdef from
it. */
if (!last_vdef)
last_vdef = gimple_phi_arg_def (vphi, 0);
imm_use_iterator iter;
use_operand_p use_p;
gimple *use_stmt;
@ -2711,7 +2674,63 @@ combine_blocks (class loop *loop)
gimple_stmt_iterator gsi = gsi_for_stmt (vphi);
remove_phi_node (&gsi, true);
}
}
/* Now remove all the edges in the loop, except for those from the exit
block and delete the blocks we elided. */
for (i = 1; i < orig_loop_num_nodes; i++)
{
bb = ifc_bbs[i];
for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei));)
{
if (e->src == exit_bb)
ei_next (&ei);
else
remove_edge (e);
}
}
for (i = 1; i < orig_loop_num_nodes; i++)
{
bb = ifc_bbs[i];
if (bb == exit_bb || bb == loop->latch)
continue;
delete_basic_block (bb);
}
/* Re-connect the exit block. */
if (exit_bb != NULL)
{
if (exit_bb != loop->header)
{
/* Connect this node to loop header. */
make_single_succ_edge (loop->header, exit_bb, EDGE_FALLTHRU);
set_immediate_dominator (CDI_DOMINATORS, exit_bb, loop->header);
}
/* Redirect non-exit edges to loop->latch. */
FOR_EACH_EDGE (e, ei, exit_bb->succs)
{
if (!loop_exit_edge_p (loop, e))
redirect_edge_and_branch (e, loop->latch);
}
set_immediate_dominator (CDI_DOMINATORS, loop->latch, exit_bb);
}
else
{
/* If the loop does not have an exit, reconnect header and latch. */
make_edge (loop->header, loop->latch, EDGE_FALLTHRU);
set_immediate_dominator (CDI_DOMINATORS, loop->latch, loop->header);
}
/* If possible, merge loop header to the block with the exit edge.
This reduces the number of basic blocks to two, to please the
vectorizer that handles only loops with two nodes. */
if (exit_bb
&& exit_bb != loop->header)
{
if (can_merge_blocks_p (loop->header, exit_bb))
merge_blocks (loop->header, exit_bb);
}