------- Additional Comments From sebastian dot pop at cri dot ensmp dot fr
2005-09-21 17:02 -------
Subject: Re: [4.1 Regression] loop problem / testcase takes very long time to
compile
> Random break stops things typically somewhere inside 140 nested calls in scev
> (follow_ssa_edge and friends). I seem to recall there is some backtracking
> involved, I will check.
>
A patch around these lines should fix the problem: it limits the
number of arcs that we walk before giving up. For the moment I'm
returning "didn't found a path from P to P", when we give up. We have
to handle a "don't know" symbol for this case.
I'll test a patch similar to the following tomorow.
Index: Makefile.in
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Makefile.in,v
retrieving revision 1.1541
diff -d -u -p -r1.1541 Makefile.in
--- Makefile.in 14 Sep 2005 09:26:41 -0000 1.1541
+++ Makefile.in 21 Sep 2005 16:51:48 -0000
@@ -767,7 +767,7 @@ TREE_SSA_LIVE_H = tree-ssa-live.h $(PART
PRETTY_PRINT_H = pretty-print.h input.h $(OBSTACK_H)
DIAGNOSTIC_H = diagnostic.h diagnostic.def $(PRETTY_PRINT_H)
C_PRETTY_PRINT_H = c-pretty-print.h $(PRETTY_PRINT_H) $(C_COMMON_H) $(TREE_H)
-SCEV_H = tree-scalar-evolution.h $(GGC_H) tree-chrec.h
+SCEV_H = tree-scalar-evolution.h $(GGC_H) tree-chrec.h $(PARAMS_H)
LAMBDA_H = lambda.h tree.h vec.h $(GGC_H)
TREE_DATA_REF_H = tree-data-ref.h $(LAMBDA_H)
VARRAY_H = varray.h $(MACHMODE_H) $(SYSTEM_H) coretypes.h $(TM_H)
Index: tree-scalar-evolution.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-scalar-evolution.c,v
retrieving revision 2.38
diff -d -u -p -r2.38 tree-scalar-evolution.c
--- tree-scalar-evolution.c 20 Sep 2005 07:09:20 -0000 2.38
+++ tree-scalar-evolution.c 21 Sep 2005 16:51:48 -0000
@@ -251,6 +251,7 @@ Software Foundation, 51 Franklin Street,
#include "tree-scalar-evolution.h"
#include "tree-pass.h"
#include "flags.h"
+#include "params.h"
static tree analyze_scalar_evolution_1 (struct loop *, tree, tree);
static tree resolve_mixers (struct loop *, tree);
@@ -1022,17 +1023,14 @@ select_loops_exit_conditions (struct loo
/* Depth first search algorithm. */
-static bool follow_ssa_edge (struct loop *loop, tree, tree, tree *);
+static bool follow_ssa_edge (struct loop *loop, tree, tree, tree *, int);
/* Follow the ssa edge into the right hand side RHS of an assignment.
Return true if the strongly connected component has been found. */
static bool
-follow_ssa_edge_in_rhs (struct loop *loop,
- tree at_stmt,
- tree rhs,
- tree halting_phi,
- tree *evolution_of_loop)
+follow_ssa_edge_in_rhs (struct loop *loop, tree at_stmt, tree rhs,
+ tree halting_phi, tree *evolution_of_loop, int limit)
{
bool res = false;
tree rhs0, rhs1;
@@ -1050,7 +1048,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
case NOP_EXPR:
/* This assignment is under the form "a_1 = (cast) rhs. */
res = follow_ssa_edge_in_rhs (loop, at_stmt, TREE_OPERAND (rhs, 0),
- halting_phi, evolution_of_loop);
+ halting_phi, evolution_of_loop, limit);
*evolution_of_loop = chrec_convert (TREE_TYPE (rhs),
*evolution_of_loop, at_stmt);
break;
@@ -1063,7 +1061,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
case SSA_NAME:
/* This assignment is under the form: "a_1 = b_2". */
res = follow_ssa_edge
- (loop, SSA_NAME_DEF_STMT (rhs), halting_phi, evolution_of_loop);
+ (loop, SSA_NAME_DEF_STMT (rhs), halting_phi, evolution_of_loop, limit);
break;
case PLUS_EXPR:
@@ -1081,7 +1079,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
"a = b + c". */
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs0), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = add_to_evolution
@@ -1093,7 +1091,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
{
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs1), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = add_to_evolution
@@ -1109,7 +1107,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
"a = b + ...". */
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs0), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = add_to_evolution
(loop->num, chrec_convert (type_rhs, *evolution_of_loop,
@@ -1124,7 +1122,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
"a = ... + c". */
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs1), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = add_to_evolution
(loop->num, chrec_convert (type_rhs, *evolution_of_loop,
@@ -1152,7 +1150,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
/* Match an assignment under the form:
"a = b - ...". */
res = follow_ssa_edge (loop, SSA_NAME_DEF_STMT (rhs0), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = add_to_evolution
(loop->num, chrec_convert (type_rhs, *evolution_of_loop,
@@ -1182,7 +1180,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
"a = b * c". */
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs0), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = chrec_dont_know;
@@ -1191,7 +1189,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
{
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs1), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = chrec_dont_know;
@@ -1204,7 +1202,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
"a = b * ...". */
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs0), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = chrec_dont_know;
}
@@ -1216,7 +1214,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
"a = ... * c". */
res = follow_ssa_edge
(loop, SSA_NAME_DEF_STMT (rhs1), halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
if (res)
*evolution_of_loop = chrec_dont_know;
}
@@ -1236,7 +1234,7 @@ follow_ssa_edge_in_rhs (struct loop *loo
tree op0 = ASSERT_EXPR_VAR (rhs);
if (TREE_CODE (op0) == SSA_NAME)
res = follow_ssa_edge (loop, SSA_NAME_DEF_STMT (op0),
- halting_phi, evolution_of_loop);
+ halting_phi, evolution_of_loop, limit);
else
res = false;
break;
@@ -1277,7 +1275,7 @@ follow_ssa_edge_in_condition_phi_branch
tree condition_phi,
tree halting_phi,
tree *evolution_of_branch,
- tree init_cond)
+ tree init_cond, int limit)
{
tree branch = PHI_ARG_DEF (condition_phi, i);
*evolution_of_branch = chrec_dont_know;
@@ -1291,7 +1289,7 @@ follow_ssa_edge_in_condition_phi_branch
{
*evolution_of_branch = init_cond;
return follow_ssa_edge (loop, SSA_NAME_DEF_STMT (branch), halting_phi,
- evolution_of_branch);
+ evolution_of_branch, limit);
}
/* This case occurs when one of the condition branches sets
@@ -1311,7 +1309,7 @@ static bool
follow_ssa_edge_in_condition_phi (struct loop *loop,
tree condition_phi,
tree halting_phi,
- tree *evolution_of_loop)
+ tree *evolution_of_loop, int limit)
{
int i;
tree init = *evolution_of_loop;
@@ -1320,7 +1318,7 @@ follow_ssa_edge_in_condition_phi (struct
if (!follow_ssa_edge_in_condition_phi_branch (0, loop, condition_phi,
halting_phi,
&evolution_of_branch,
- init))
+ init, limit))
return false;
*evolution_of_loop = evolution_of_branch;
@@ -1334,7 +1332,7 @@ follow_ssa_edge_in_condition_phi (struct
if (!follow_ssa_edge_in_condition_phi_branch (i, loop, condition_phi,
halting_phi,
&evolution_of_branch,
- init))
+ init, limit))
return false;
*evolution_of_loop = chrec_merge (*evolution_of_loop,
@@ -1353,7 +1351,7 @@ static bool
follow_ssa_edge_inner_loop_phi (struct loop *outer_loop,
tree loop_phi_node,
tree halting_phi,
- tree *evolution_of_loop)
+ tree *evolution_of_loop, int limit)
{
struct loop *loop = loop_containing_stmt (loop_phi_node);
tree ev = analyze_scalar_evolution (loop, PHI_RESULT (loop_phi_node));
@@ -1375,7 +1373,7 @@ follow_ssa_edge_inner_loop_phi (struct l
if (!flow_bb_inside_loop_p (loop, bb))
res = res || follow_ssa_edge_in_rhs (outer_loop, loop_phi_node,
arg, halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
}
/* If the path crosses this loop-phi, give up. */
@@ -1388,21 +1386,20 @@ follow_ssa_edge_inner_loop_phi (struct l
/* Otherwise, compute the overall effect of the inner loop. */
ev = compute_overall_effect_of_inner_loop (loop, ev);
return follow_ssa_edge_in_rhs (outer_loop, loop_phi_node, ev, halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
}
/* Follow an SSA edge from a loop-phi-node to itself, constructing a
path that is analyzed on the return walk. */
static bool
-follow_ssa_edge (struct loop *loop,
- tree def,
- tree halting_phi,
- tree *evolution_of_loop)
+follow_ssa_edge (struct loop *loop, tree def, tree halting_phi,
+ tree *evolution_of_loop, int limit)
{
struct loop *def_loop;
- if (TREE_CODE (def) == NOP_EXPR)
+ if (limit++ > PARAM_VALUE (PARAM_SCEV_MAX_EXPR_SIZE)
+ || TREE_CODE (def) == NOP_EXPR)
return false;
def_loop = loop_containing_stmt (def);
@@ -1416,7 +1413,7 @@ follow_ssa_edge (struct loop *loop,
information and set the approximation to the main
variable. */
return follow_ssa_edge_in_condition_phi
- (loop, def, halting_phi, evolution_of_loop);
+ (loop, def, halting_phi, evolution_of_loop, limit);
/* When the analyzed phi is the halting_phi, the
depth-first search is over: we have found a path from
@@ -1433,7 +1430,7 @@ follow_ssa_edge (struct loop *loop,
/* Inner loop. */
if (flow_loop_nested_p (loop, def_loop))
return follow_ssa_edge_inner_loop_phi
- (loop, def, halting_phi, evolution_of_loop);
+ (loop, def, halting_phi, evolution_of_loop, limit);
/* Outer loop. */
return false;
@@ -1442,7 +1439,7 @@ follow_ssa_edge (struct loop *loop,
return follow_ssa_edge_in_rhs (loop, def,
TREE_OPERAND (def, 1),
halting_phi,
- evolution_of_loop);
+ evolution_of_loop, limit);
default:
/* At this level of abstraction, the program is just a set
@@ -1491,7 +1488,7 @@ analyze_evolution_in_loop (tree loop_phi
/* Pass in the initial condition to the follow edge function. */
ev_fn = init_cond;
- res = follow_ssa_edge (loop, ssa_chain, loop_phi_node, &ev_fn);
+ res = follow_ssa_edge (loop, ssa_chain, loop_phi_node, &ev_fn, 0);
}
else
res = false;
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23942
