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re PR tree-optimization/52943 (likely wrong code bug caused by predictive commoning)

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2012-04-12  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/52943
	* tree-chrec.h (chrec_is_positive): Remove.
	* tree-scalar-evolution.c (chrec_is_positive): Move ...
	* tree-data-ref.c (chrec_is_positive): ... here.  Make static.
	Return false for a constant zero instead of negative.
	(analyze_siv_subscript_cst_affine): Handle zero difference
	in the initial condition explicitely.

	* gcc.dg/torture/pr52943.c: New testcase.

From-SVN: r186374
This commit is contained in:
Richard Guenther 2012-04-12 11:38:47 +00:00 committed by Richard Biener
parent e5b332cdb8
commit 5f1fab5819
6 changed files with 114 additions and 60 deletions
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10
gcc/ChangeLog
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@ -1,3 +1,13 @@
2012-04-12 Richard Guenther <rguenther@suse.de>
PR tree-optimization/52943
* tree-chrec.h (chrec_is_positive): Remove.
* tree-scalar-evolution.c (chrec_is_positive): Move ...
* tree-data-ref.c (chrec_is_positive): ... here. Make static.
Return false for a constant zero instead of negative.
(analyze_siv_subscript_cst_affine): Handle zero difference
in the initial condition explicitely.
2012-04-12 Richard Guenther <rguenther@suse.de>
* tree-parloops.c (parallelize_loops): Also consult the upper

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2012-04-12 Richard Guenther <rguenther@suse.de>
PR tree-optimization/52943
* gcc.dg/torture/pr52943.c: New testcase.
2012-04-12 Oleg Endo <olegendo@gcc.gnu.org>
PR target/50751

20
gcc/testsuite/gcc.dg/torture/pr52943.c Normal file
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@ -0,0 +1,20 @@
/* { dg-do run } */
extern void abort (void);
int a[] = { 0, 0, 0, 6 };
int b;
int
main ()
{
for (;;)
{
b = 3;
for (; b; b -= 1)
a[b] = a[3] > 1;
break;
}
if (a[1] != 0)
abort ();
return 0;
}

1
gcc/tree-chrec.h
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@ -77,7 +77,6 @@ extern void for_each_scev_op (tree *, bool (*) (tree *, void *), void *);
/* Observers. */
extern bool eq_evolutions_p (const_tree, const_tree);
extern bool is_multivariate_chrec (const_tree);
extern bool chrec_is_positive (tree, bool *);
extern bool chrec_contains_symbols (const_tree);
extern bool chrec_contains_symbols_defined_in_loop (const_tree, unsigned);
extern bool chrec_contains_undetermined (const_tree);

79
gcc/tree-data-ref.c
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@ -1718,6 +1718,76 @@ max_stmt_executions_tree (struct loop *loop)
return double_int_to_tree (unsigned_type_node, nit);
}
/* Determine whether the CHREC is always positive/negative. If the expression
cannot be statically analyzed, return false, otherwise set the answer into
VALUE. */
static bool
chrec_is_positive (tree chrec, bool *value)
{
bool value0, value1, value2;
tree end_value, nb_iter;
switch (TREE_CODE (chrec))
{
case POLYNOMIAL_CHREC:
if (!chrec_is_positive (CHREC_LEFT (chrec), &value0)
|| !chrec_is_positive (CHREC_RIGHT (chrec), &value1))
return false;
/* FIXME -- overflows. */
if (value0 == value1)
{
*value = value0;
return true;
}
/* Otherwise the chrec is under the form: "{-197, +, 2}_1",
and the proof consists in showing that the sign never
changes during the execution of the loop, from 0 to
loop->nb_iterations. */
if (!evolution_function_is_affine_p (chrec))
return false;
nb_iter = number_of_latch_executions (get_chrec_loop (chrec));
if (chrec_contains_undetermined (nb_iter))
return false;
#if 0
/* TODO -- If the test is after the exit, we may decrease the number of
iterations by one. */
if (after_exit)
nb_iter = chrec_fold_minus (type, nb_iter, build_int_cst (type, 1));
#endif
end_value = chrec_apply (CHREC_VARIABLE (chrec), chrec, nb_iter);
if (!chrec_is_positive (end_value, &value2))
return false;
*value = value0;
return value0 == value1;
case INTEGER_CST:
switch (tree_int_cst_sgn (chrec))
{
case -1:
*value = false;
break;
case 1:
*value = true;
break;
default:
return false;
}
return true;
default:
return false;
}
}
/* Analyze a SIV (Single Index Variable) subscript where CHREC_A is a
constant, and CHREC_B is an affine function. *OVERLAPS_A and
*OVERLAPS_B are initialized to the functions that describe the
@ -1741,6 +1811,15 @@ analyze_siv_subscript_cst_affine (tree chrec_a,
chrec_b = chrec_convert (type, chrec_b, NULL);
difference = chrec_fold_minus (type, initial_condition (chrec_b), chrec_a);
/* Special case overlap in the first iteration. */
if (integer_zerop (difference))
{
*overlaps_a = conflict_fn (1, affine_fn_cst (integer_zero_node));
*overlaps_b = conflict_fn (1, affine_fn_cst (integer_zero_node));
*last_conflicts = integer_one_node;
return;
}
if (!chrec_is_positive (initial_condition (difference), &value0))
{
if (dump_file && (dump_flags & TDF_DETAILS))

59
gcc/tree-scalar-evolution.c
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@ -501,65 +501,6 @@ compute_overall_effect_of_inner_loop (struct loop *loop, tree evolution_fn)
return chrec_dont_know;
}
/* Determine whether the CHREC is always positive/negative. If the expression
cannot be statically analyzed, return false, otherwise set the answer into
VALUE. */
bool
chrec_is_positive (tree chrec, bool *value)
{
bool value0, value1, value2;
tree end_value, nb_iter;
switch (TREE_CODE (chrec))
{
case POLYNOMIAL_CHREC:
if (!chrec_is_positive (CHREC_LEFT (chrec), &value0)
|| !chrec_is_positive (CHREC_RIGHT (chrec), &value1))
return false;
/* FIXME -- overflows. */
if (value0 == value1)
{
*value = value0;
return true;
}
/* Otherwise the chrec is under the form: "{-197, +, 2}_1",
and the proof consists in showing that the sign never
changes during the execution of the loop, from 0 to
loop->nb_iterations. */
if (!evolution_function_is_affine_p (chrec))
return false;
nb_iter = number_of_latch_executions (get_chrec_loop (chrec));
if (chrec_contains_undetermined (nb_iter))
return false;
#if 0
/* TODO -- If the test is after the exit, we may decrease the number of
iterations by one. */
if (after_exit)
nb_iter = chrec_fold_minus (type, nb_iter, build_int_cst (type, 1));
#endif
end_value = chrec_apply (CHREC_VARIABLE (chrec), chrec, nb_iter);
if (!chrec_is_positive (end_value, &value2))
return false;
*value = value0;
return value0 == value1;
case INTEGER_CST:
*value = (tree_int_cst_sgn (chrec) == 1);
return true;
default:
return false;
}
}
/* Associate CHREC to SCALAR. */
static void