This does a cleanup I postponed for GCC 8, namely not fail value-numbering
completely if we end up with a large SCC but instead just drop that SCC
to varying.
Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
Richard.
2017-04-24 Richard Biener <rguent...@suse.de>
* tree-ssa-sccvn.h (run_scc_vn): Adjust prototype.
* tree-ssa-sccvn.c (print_scc): Print SCC size.
(extract_and_process_scc_for_name): Never fail but drop SCC to varying.
(DFS): Adjust and never fail.
(sccvn_dom_walker::fail): Remove.
(sccvn_dom_walker::before_dom_children): Adjust.
(run_scc_vn): Likewise and never fail.
* tree-ssa-pre.c (pass_pre::execute): Adjust.
(pass_fre::execute): Likewise.
Index: gcc/tree-ssa-pre.c
===================================================================
--- gcc/tree-ssa-pre.c (revision 247091)
+++ gcc/tree-ssa-pre.c (working copy)
@@ -5086,11 +5086,7 @@ pass_pre::execute (function *fun)
loop_optimizer_init may create new phis, etc. */
loop_optimizer_init (LOOPS_NORMAL);
- if (!run_scc_vn (VN_WALK))
- {
- loop_optimizer_finalize ();
- return 0;
- }
+ run_scc_vn (VN_WALK);
init_pre ();
scev_initialize ();
@@ -5202,8 +5198,7 @@ pass_fre::execute (function *fun)
{
unsigned int todo = 0;
- if (!run_scc_vn (VN_WALKREWRITE))
- return 0;
+ run_scc_vn (VN_WALKREWRITE);
memset (&pre_stats, 0, sizeof (pre_stats));
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 247091)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -3153,7 +3153,7 @@ print_scc (FILE *out, vec<tree> scc)
tree var;
unsigned int i;
- fprintf (out, "SCC consists of:");
+ fprintf (out, "SCC consists of %u:", scc.length ());
FOR_EACH_VEC_ELT (scc, i, var)
{
fprintf (out, " ");
@@ -4316,7 +4316,7 @@ process_scc (vec<tree> scc)
and process them. Returns true if all went well, false if
we run into resource limits. */
-static bool
+static void
extract_and_process_scc_for_name (tree name)
{
auto_vec<tree> scc;
@@ -4332,24 +4332,37 @@ extract_and_process_scc_for_name (tree n
scc.safe_push (x);
} while (x != name);
- /* Bail out of SCCVN in case a SCC turns out to be incredibly large. */
- if (scc.length ()
- > (unsigned)PARAM_VALUE (PARAM_SCCVN_MAX_SCC_SIZE))
+ /* Drop all defs in the SCC to varying in case a SCC turns out to be
+ incredibly large.
+ ??? Just switch to a non-optimistic mode that avoids any iteration. */
+ if (scc.length () > (unsigned)PARAM_VALUE (PARAM_SCCVN_MAX_SCC_SIZE))
{
if (dump_file)
- fprintf (dump_file, "WARNING: Giving up with SCCVN due to "
- "SCC size %u exceeding %u\n", scc.length (),
- (unsigned)PARAM_VALUE (PARAM_SCCVN_MAX_SCC_SIZE));
-
- return false;
+ {
+ print_scc (dump_file, scc);
+ fprintf (dump_file, "WARNING: Giving up value-numbering SCC due to "
+ "size %u exceeding %u\n", scc.length (),
+ (unsigned)PARAM_VALUE (PARAM_SCCVN_MAX_SCC_SIZE));
+ }
+ tree var;
+ unsigned i;
+ FOR_EACH_VEC_ELT (scc, i, var)
+ {
+ gimple *def = SSA_NAME_DEF_STMT (var);
+ mark_use_processed (var);
+ if (SSA_NAME_IS_DEFAULT_DEF (var)
+ || gimple_code (def) == GIMPLE_PHI)
+ set_ssa_val_to (var, var);
+ else
+ defs_to_varying (def);
+ }
+ return;
}
if (scc.length () > 1)
sort_scc (scc);
process_scc (scc);
-
- return true;
}
/* Depth first search on NAME to discover and process SCC's in the SSA
@@ -4359,7 +4372,7 @@ extract_and_process_scc_for_name (tree n
Returns true if successful, false if we stopped processing SCC's due
to resource constraints. */
-static bool
+static void
DFS (tree name)
{
auto_vec<ssa_op_iter> itervec;
@@ -4399,12 +4412,11 @@ start_over:
{
/* See if we found an SCC. */
if (VN_INFO (name)->low == VN_INFO (name)->dfsnum)
- if (!extract_and_process_scc_for_name (name))
- return false;
+ extract_and_process_scc_for_name (name);
/* Check if we are done. */
if (namevec.is_empty ())
- return true;
+ return;
/* Restore the last use walker and continue walking there. */
use = name;
@@ -4687,7 +4699,7 @@ class sccvn_dom_walker : public dom_walk
{
public:
sccvn_dom_walker ()
- : dom_walker (CDI_DOMINATORS, true), fail (false), cond_stack (0) {}
+ : dom_walker (CDI_DOMINATORS, true), cond_stack (0) {}
virtual edge before_dom_children (basic_block);
virtual void after_dom_children (basic_block);
@@ -4697,7 +4709,6 @@ public:
void record_conds (basic_block,
enum tree_code code, tree lhs, tree rhs, bool value);
- bool fail;
auto_vec<std::pair <basic_block, std::pair <vn_nary_op_t, vn_nary_op_t> > >
cond_stack;
};
@@ -4793,9 +4804,6 @@ sccvn_dom_walker::before_dom_children (b
edge e;
edge_iterator ei;
- if (fail)
- return NULL;
-
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Visiting BB %d\n", bb->index);
@@ -4851,12 +4859,8 @@ sccvn_dom_walker::before_dom_children (b
{
gphi *phi = gsi.phi ();
tree res = PHI_RESULT (phi);
- if (!VN_INFO (res)->visited
- && !DFS (res))
- {
- fail = true;
- return NULL;
- }
+ if (!VN_INFO (res)->visited)
+ DFS (res);
}
for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
!gsi_end_p (gsi); gsi_next (&gsi))
@@ -4864,12 +4868,8 @@ sccvn_dom_walker::before_dom_children (b
ssa_op_iter i;
tree op;
FOR_EACH_SSA_TREE_OPERAND (op, gsi_stmt (gsi), i, SSA_OP_ALL_DEFS)
- if (!VN_INFO (op)->visited
- && !DFS (op))
- {
- fail = true;
- return NULL;
- }
+ if (!VN_INFO (op)->visited)
+ DFS (op);
}
/* Finally look at the last stmt. */
@@ -4941,7 +4941,7 @@ sccvn_dom_walker::before_dom_children (b
due to resource constraints. DEFAULT_VN_WALK_KIND_ specifies
how we use the alias oracle walking during the VN process. */
-bool
+void
run_scc_vn (vn_lookup_kind default_vn_walk_kind_)
{
size_t i;
@@ -4977,12 +4977,6 @@ run_scc_vn (vn_lookup_kind default_vn_wa
SSA defs and decide whether outgoing edges are not executable. */
sccvn_dom_walker walker;
walker.walk (ENTRY_BLOCK_PTR_FOR_FN (cfun));
- if (walker.fail)
- {
- scc_vn_restore_ssa_info ();
- free_scc_vn ();
- return false;
- }
/* Initialize the value ids and prune out remaining VN_TOPs
from dead code. */
@@ -5027,8 +5021,6 @@ run_scc_vn (vn_lookup_kind default_vn_wa
}
}
}
-
- return true;
}
/* Return the maximum value id we have ever seen. */
Index: gcc/tree-ssa-sccvn.h
===================================================================
--- gcc/tree-ssa-sccvn.h (revision 247091)
+++ gcc/tree-ssa-sccvn.h (working copy)
@@ -212,7 +212,7 @@ enum vn_lookup_kind { VN_NOWALK, VN_WALK
extern vn_ssa_aux_t VN_INFO (tree);
extern vn_ssa_aux_t VN_INFO_GET (tree);
tree vn_get_expr_for (tree);
-bool run_scc_vn (vn_lookup_kind);
+void run_scc_vn (vn_lookup_kind);
void free_scc_vn (void);
void scc_vn_restore_ssa_info (void);
tree vn_nary_op_lookup (tree, vn_nary_op_t *);
