Here's the revised patch with a param. Bootstrapped and tested in the
same manner. Ok for trunk?
Thanks,
Bill
2012-08-10 Bill Schmidt <wschm...@linux.vnet.ibm.com>
* doc/invoke.texi (max-slsr-cand-scan): New description.
* gimple-ssa-strength-reduction.c (find_basis_for_candidate): Limit
the time spent searching for a basis.
* params.def (PARAM_MAX_SLSR_CANDIDATE_SCAN): New param.
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi (revision 191135)
+++ gcc/doc/invoke.texi (working copy)
@@ -9407,6 +9407,11 @@ having a regular register file and accurate regist
See @file{haifa-sched.c} in the GCC sources for more details.
The default choice depends on the target.
+
+@item max-slsr-cand-scan
+Set the maximum number of existing candidates that will be considered when
+seeking a basis for a new straight-line strength reduction candidate.
+
@end table
@end table
Index: gcc/gimple-ssa-strength-reduction.c
===================================================================
--- gcc/gimple-ssa-strength-reduction.c (revision 191135)
+++ gcc/gimple-ssa-strength-reduction.c (working copy)
@@ -54,6 +54,7 @@ along with GCC; see the file COPYING3. If not see
#include "domwalk.h"
#include "pointer-set.h"
#include "expmed.h"
+#include "params.h"
/* Information about a strength reduction candidate. Each statement
in the candidate table represents an expression of one of the
@@ -353,10 +354,14 @@ find_basis_for_candidate (slsr_cand_t c)
cand_chain_t chain;
slsr_cand_t basis = NULL;
+ // Limit potential of N^2 behavior for long candidate chains.
+ int iters = 0;
+ int max_iters = PARAM_VALUE (PARAM_MAX_SLSR_CANDIDATE_SCAN);
+
mapping_key.base_expr = c->base_expr;
chain = (cand_chain_t) htab_find (base_cand_map, &mapping_key);
- for (; chain; chain = chain->next)
+ for (; chain && iters < max_iters; chain = chain->next, ++iters)
{
slsr_cand_t one_basis = chain->cand;
Index: gcc/params.def
===================================================================
--- gcc/params.def (revision 191135)
+++ gcc/params.def (working copy)
@@ -973,6 +973,13 @@ DEFPARAM (PARAM_SCHED_PRESSURE_ALGORITHM,
"Which -fsched-pressure algorithm to apply",
1, 1, 2)
+/* Maximum length of candidate scans in straight-line strength reduction. */
+DEFPARAM (PARAM_MAX_SLSR_CANDIDATE_SCAN,
+ "max-slsr-cand-scan",
+ "Maximum length of candidate scans for straight-line "
+ "strength reduction",
+ 50, 1, 999999)
+
/*
Local variables:
mode:c
