Hi,
After control flow graph change made by
http://gcc.gnu.org/ml/gcc-patches/2014-02/msg01492.html, case
gcc.dg/tree-ssa/ssa-dom-thread-4.c is broken on logical_op_short_circuit
targets including cortex-m3/cortex-m0.
The regression reveals a missed opportunity in jump threading, which causes
a forward basic block doesn't get removed in cfgcleanup after jump threading
in VRP1. Root cause is stated at the corresponding PR:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60363, please refer to it for
detailed report.
This patch fixes the issue by adding constant value instead of ssa_name as
the new phi argument. Bootstrap and test on x86_64, also test on cortex-m3
and the regression is gone.
I think this should wait for stage1, but would like to hear some comments
now. So does it look reasonable?
2014-03-18 Bin Cheng <bin.ch...@arm.com>
PR regression/60363
* gcc/tree-ssa-threadupdate.c (get_value_locus_in_path): New.
(copy_phi_args): New parameters. Call get_value_locus_in_path.
(update_destination_phis): New parameter.
(create_edge_and_update_destination_phis): Ditto.
(ssa_fix_duplicate_block_edges): Pass new arguments.
(thread_single_edge): Ditto.
Index: gcc/tree-ssa-threadupdate.c
===================================================================
--- gcc/tree-ssa-threadupdate.c (revision 208609)
+++ gcc/tree-ssa-threadupdate.c (working copy)
@@ -403,10 +403,51 @@ copy_phi_arg_into_existing_phi (edge src_e, edge t
}
}
-/* For each PHI in BB, copy the argument associated with SRC_E to TGT_E. */
+/* Given ssa_name DEF, backtrack jump threading PATH from node IDX
+ to see if it has constant value in a flow sensitive manner. Set
+ LOCUS to location of the constant phi arg and return the value.
+ Return DEF directly if either PATH or idx is ZERO. */
+static tree
+get_value_locus_in_path (tree def, vec<jump_thread_edge *> *path,
+ int idx, source_location *locus)
+{
+ tree arg;
+ gimple def_phi;
+ basic_block def_bb;
+
+ if (path == NULL || idx == 0)
+ return def;
+
+ def_phi = SSA_NAME_DEF_STMT (def);
+ if (gimple_code (def_phi) != GIMPLE_PHI)
+ return def;
+
+ def_bb = gimple_bb (def_phi);
+ /* Backtrack jump threading path from IDX to see if def has constant
+ value. */
+ for (int j = idx - 1; j >= 0; j--)
+ {
+ edge e = (*path)[j]->e;
+ if (e->dest == def_bb)
+ {
+ arg = gimple_phi_arg_def (def_phi, e->dest_idx);
+ *locus = gimple_phi_arg_location (def_phi, e->dest_idx);
+ return (TREE_CODE (arg) == INTEGER_CST ? arg : def);
+ }
+ }
+
+ return def;
+}
+
+/* For each PHI in BB, copy the argument associated with SRC_E to TGT_E.
+ Try to backtrack jump threading PATH from node IDX to see if the arg
+ has constant value, copy constant value instead of argument itself
+ if yes. */
+
static void
-copy_phi_args (basic_block bb, edge src_e, edge tgt_e)
+copy_phi_args (basic_block bb, edge src_e, edge tgt_e,
+ vec<jump_thread_edge *> *path, int idx)
{
gimple_stmt_iterator gsi;
int src_indx = src_e->dest_idx;
@@ -414,8 +455,14 @@ static void
for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple phi = gsi_stmt (gsi);
+ tree def = gimple_phi_arg_def (phi, src_indx);
source_location locus = gimple_phi_arg_location (phi, src_indx);
- add_phi_arg (phi, gimple_phi_arg_def (phi, src_indx), tgt_e, locus);
+
+ if (TREE_CODE (def) == SSA_NAME
+ && !virtual_operand_p (gimple_phi_result (phi)))
+ def = get_value_locus_in_path (def, path, idx, &locus);
+
+ add_phi_arg (phi, def, tgt_e, locus);
}
}
@@ -423,10 +470,13 @@ static void
edges. The copy is NEW_BB. Every PHI node in every direct successor of
ORIG_BB has a new argument associated with edge from NEW_BB to the
successor. Initialize the PHI argument so that it is equal to the PHI
- argument associated with the edge from ORIG_BB to the successor. */
+ argument associated with the edge from ORIG_BB to the successor.
+ PATH and IDX are used to check if the new PHI argument has constant
+ value in a flow sensitive manner. */
static void
-update_destination_phis (basic_block orig_bb, basic_block new_bb)
+update_destination_phis (basic_block orig_bb, basic_block new_bb,
+ vec<jump_thread_edge *> *path, int idx)
{
edge_iterator ei;
edge e;
@@ -434,7 +484,7 @@ static void
FOR_EACH_EDGE (e, ei, orig_bb->succs)
{
edge e2 = find_edge (new_bb, e->dest);
- copy_phi_args (e->dest, e, e2);
+ copy_phi_args (e->dest, e, e2, path, idx);
}
}
@@ -443,11 +493,13 @@ static void
destination.
Add an additional argument to any PHI nodes at the single
- destination. */
+ destination. IDX is the start node in jump threading path
+ we start to check to see if the new PHI argument has constant
+ value along the jump threading path. */
static void
create_edge_and_update_destination_phis (struct redirection_data *rd,
- basic_block bb)
+ basic_block bb, int idx)
{
edge e = make_edge (bb, rd->path->last ()->e->dest, EDGE_FALLTHRU);
@@ -476,7 +528,7 @@ create_edge_and_update_destination_phis (struct re
from the duplicate block, then we will need to add a new argument
to them. The argument should have the same value as the argument
associated with the outgoing edge stored in RD. */
- copy_phi_args (e->dest, rd->path->last ()->e, e);
+ copy_phi_args (e->dest, rd->path->last ()->e, e, rd->path, idx);
}
/* Look through PATH beginning at START and return TRUE if there are
@@ -501,6 +553,7 @@ void
ssa_fix_duplicate_block_edges (struct redirection_data *rd,
ssa_local_info_t *local_info)
{
+ bool mult_incomings = (rd->incoming_edges->next != NULL);
edge e = rd->incoming_edges->e;
vec<jump_thread_edge *> *path = THREAD_PATH (e);
@@ -516,8 +569,10 @@ ssa_fix_duplicate_block_edges (struct redirection_
edge e2;
/* This updates the PHIs at the destination of the duplicate
- block. */
- update_destination_phis (local_info->bb, rd->dup_blocks[count]);
+ block. Pass 0 instead of i if we are threading a path which
+ has multiple incoming edges. */
+ update_destination_phis (local_info->bb, rd->dup_blocks[count],
+ path, mult_incomings ? i : 0);
/* Find the edge from the duplicate block to the block we're
threading through. That's the edge we want to redirect. */
@@ -535,7 +590,8 @@ ssa_fix_duplicate_block_edges (struct redirection_
case), then the PHIs in the target already have the correct
arguments. */
if (e2 == victim)
- copy_phi_args (e2->dest, path->last ()->e, e2);
+ copy_phi_args (e2->dest, path->last ()->e, e2,
+ path, mult_incomings ? i : 0);
}
else
{
@@ -567,7 +623,8 @@ ssa_fix_duplicate_block_edges (struct redirection_
else if ((*path)[i]->type == EDGE_COPY_SRC_BLOCK)
{
remove_ctrl_stmt_and_useless_edges (rd->dup_blocks[count], NULL);
- create_edge_and_update_destination_phis (rd, rd->dup_blocks[count]);
+ create_edge_and_update_destination_phis (rd, rd->dup_blocks[count],
+ mult_incomings ? i : 0);
if (count == 1)
single_succ_edge (rd->dup_blocks[1])->aux = NULL;
count++;
@@ -989,7 +1046,7 @@ thread_single_edge (edge e)
create_block_for_threading (bb, &rd, 0);
remove_ctrl_stmt_and_useless_edges (rd.dup_blocks[0], NULL);
- create_edge_and_update_destination_phis (&rd, rd.dup_blocks[0]);
+ create_edge_and_update_destination_phis (&rd, rd.dup_blocks[0], 0);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
