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Improve forward jump threading of switch statements (PR18046)

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gcc/ChangeLog:

	PR tree-optimization/18046
	* tree-ssa-threadedge.c: Include cfganal.h.
	(simplify_control_statement_condition): If simplifying a
	GIMPLE_SWITCH, replace the index operand of the GIMPLE_SWITCH
	with the dominating ASSERT_EXPR before handing it off to VRP.
	Mention that a CASE_LABEL_EXPR may be returned.
	(thread_around_empty_blocks): Adjust to handle
	simplify_control_statement_condition() returning a
	CASE_LABEL_EXPR.
	(thread_through_normal_block): Likewise.
	* tree-vrp.c (simplify_stmt_for_jump_threading): Simplify
	a switch statement by trying to determine which case label
	will be taken.

gcc/testsuite/ChangeLog:

	PR tree-optimization/18046
	* gcc.dg/tree-ssa/vrp105.c: New test.
	* gcc.dg/tree-ssa/vrp106.c: New test.

From-SVN: r239181
This commit is contained in:
Patrick Palka 2016-08-05 23:29:53 +00:00
parent b10d44efe5
commit 5c3e5002db
6 changed files with 181 additions and 6 deletions
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16
gcc/ChangeLog
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@ -1,3 +1,19 @@
2016-08-05 Patrick Palka <ppalka@gcc.gnu.org>
PR tree-optimization/18046
* tree-ssa-threadedge.c: Include cfganal.h.
(simplify_control_statement_condition): If simplifying a
GIMPLE_SWITCH, replace the index operand of the GIMPLE_SWITCH
with the dominating ASSERT_EXPR before handing it off to VRP.
Mention that a CASE_LABEL_EXPR may be returned.
(thread_around_empty_blocks): Adjust to handle
simplify_control_statement_condition() returning a
CASE_LABEL_EXPR.
(thread_through_normal_block): Likewise.
* tree-vrp.c (simplify_stmt_for_jump_threading): Simplify
a switch statement by trying to determine which case label
will be taken.
2016-08-05 Vladimir Makarov <vmakarov@redhat.com>
PR rtl-optimization/69847

6
gcc/testsuite/ChangeLog
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@ -1,3 +1,9 @@
2016-08-05 Patrick Palka <ppalka@gcc.gnu.org>
PR tree-optimization/18046
* gcc.dg/tree-ssa/vrp105.c: New test.
* gcc.dg/tree-ssa/vrp106.c: New test.
2016-08-05 Martin Sebor <msebor@redhat.com>
* g++.dg/cpp0x/constexpr-cast.C: Avoid assuming (void*)1 is spelled

37
gcc/testsuite/gcc.dg/tree-ssa/vrp105.c Normal file
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@ -0,0 +1,37 @@
/* PR tree-optimization/18046 */
/* { dg-options "-O2 -fdump-tree-vrp2-details" } */
/* { dg-final { scan-tree-dump-times "Threaded jump" 1 "vrp2" } } */
/* In the 2nd VRP pass (after PRE) we expect to thread the default label of the
1st switch straight to that of the 2nd switch. */
extern void foo (void);
extern void bar (void);
extern int i;
void
test (void)
{
switch (i)
{
case 0:
foo ();
break;
case 1:
bar ();
break;
default:
break;
}
switch (i)
{
case 0:
foo ();
break;
case 1:
bar ();
break;
default:
break;
}
}

27
gcc/testsuite/gcc.dg/tree-ssa/vrp106.c Normal file
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@ -0,0 +1,27 @@
/* PR tree-optimization/18046 */
/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
/* { dg-final { scan-tree-dump-times "Threaded jump" 1 "vrp1" } } */
/* During VRP we expect to thread the true arm of the conditional through the switch
and to the BB that corresponds to the 7 ... 9 case label. */
extern void foo (void);
extern void bar (void);
extern void baz (void);
void
test (int i)
{
if (i >= 7 && i <= 8)
foo ();
switch (i)
{
case 1:
bar ();
break;
case 7:
case 8:
case 9:
baz ();
break;
}
}

40
gcc/tree-ssa-threadedge.c
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@ -36,6 +36,7 @@ along with GCC; see the file COPYING3. If not see
#include "tree-ssa-threadedge.h"
#include "tree-ssa-dom.h"
#include "gimple-fold.h"
#include "cfganal.h"
/* To avoid code explosion due to jump threading, we limit the
number of statements we are going to copy. This variable
@ -390,7 +391,8 @@ static tree simplify_control_stmt_condition_1 (edge, gimple *,
a condition using pass specific information.
Return the simplified condition or NULL if simplification could
not be performed.
not be performed. When simplifying a GIMPLE_SWITCH, we may return
the CASE_LABEL_EXPR that will be taken.
The available expression table is referenced via AVAIL_EXPRS_STACK. */
@ -513,7 +515,21 @@ simplify_control_stmt_condition (edge e,
/* If we haven't simplified to an invariant yet, then use the
pass specific callback to try and simplify it further. */
if (cached_lhs && ! is_gimple_min_invariant (cached_lhs))
cached_lhs = (*simplify) (stmt, stmt, avail_exprs_stack);
{
if (handle_dominating_asserts && code == GIMPLE_SWITCH)
{
/* Replace the index operand of the GIMPLE_SWITCH with the
dominating ASSERT_EXPR before handing it off to VRP. If
simplification is possible, the simplified value will be a
CASE_LABEL_EXPR of the label that is proven to be taken. */
gswitch *dummy_switch = as_a<gswitch *> (gimple_copy (stmt));
gimple_switch_set_index (dummy_switch, cached_lhs);
cached_lhs = (*simplify) (dummy_switch, stmt, avail_exprs_stack);
ggc_free (dummy_switch);
}
else
cached_lhs = (*simplify) (stmt, stmt, avail_exprs_stack);
}
/* We couldn't find an invariant. But, callers of this
function may be able to do something useful with the
@ -938,9 +954,14 @@ thread_around_empty_blocks (edge taken_edge,
/* If the condition can be statically computed and we have not already
visited the destination edge, then add the taken edge to our thread
path. */
if (cond && is_gimple_min_invariant (cond))
if (cond != NULL_TREE
&& (is_gimple_min_invariant (cond)
|| TREE_CODE (cond) == CASE_LABEL_EXPR))
{
taken_edge = find_taken_edge (bb, cond);
if (TREE_CODE (cond) == CASE_LABEL_EXPR)
taken_edge = find_edge (bb, label_to_block (CASE_LABEL (cond)));
else
taken_edge = find_taken_edge (bb, cond);
if ((taken_edge->flags & EDGE_DFS_BACK) != 0)
return false;
@ -1069,9 +1090,16 @@ thread_through_normal_block (edge e,
if (!cond)
return 0;
if (is_gimple_min_invariant (cond))
if (is_gimple_min_invariant (cond)
|| TREE_CODE (cond) == CASE_LABEL_EXPR)
{
edge taken_edge = find_taken_edge (e->dest, cond);
edge taken_edge;
if (TREE_CODE (cond) == CASE_LABEL_EXPR)
taken_edge = find_edge (e->dest,
label_to_block (CASE_LABEL (cond)));
else
taken_edge = find_taken_edge (e->dest, cond);
basic_block dest = (taken_edge ? taken_edge->dest : NULL);
/* DEST could be NULL for a computed jump to an absolute

61
gcc/tree-vrp.c
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@ -10183,6 +10183,67 @@ simplify_stmt_for_jump_threading (gimple *stmt, gimple *within_stmt,
gimple_cond_rhs (cond_stmt),
within_stmt);
/* We simplify a switch statement by trying to determine which case label
will be taken. If we are successful then we return the corresponding
CASE_LABEL_EXPR. */
if (gswitch *switch_stmt = dyn_cast <gswitch *> (stmt))
{
tree op = gimple_switch_index (switch_stmt);
if (TREE_CODE (op) != SSA_NAME)
return NULL_TREE;
value_range *vr = get_value_range (op);
if ((vr->type != VR_RANGE && vr->type != VR_ANTI_RANGE)
|| symbolic_range_p (vr))
return NULL_TREE;
if (vr->type == VR_RANGE)
{
size_t i, j;
/* Get the range of labels that contain a part of the operand's
value range. */
find_case_label_range (switch_stmt, vr->min, vr->max, &i, &j);
/* Is there only one such label? */
if (i == j)
{
tree label = gimple_switch_label (switch_stmt, i);
/* The i'th label will be taken only if the value range of the
operand is entirely within the bounds of this label. */
if (CASE_HIGH (label) != NULL_TREE
? (tree_int_cst_compare (CASE_LOW (label), vr->min) <= 0
&& tree_int_cst_compare (CASE_HIGH (label), vr->max) >= 0)
: (tree_int_cst_equal (CASE_LOW (label), vr->min)
&& tree_int_cst_equal (vr->min, vr->max)))
return label;
}
/* If there are no such labels then the default label will be
taken. */
if (i > j)
return gimple_switch_label (switch_stmt, 0);
}
if (vr->type == VR_ANTI_RANGE)
{
unsigned n = gimple_switch_num_labels (switch_stmt);
tree min_label = gimple_switch_label (switch_stmt, 1);
tree max_label = gimple_switch_label (switch_stmt, n - 1);
/* The default label will be taken only if the anti-range of the
operand is entirely outside the bounds of all the (non-default)
case labels. */
if (tree_int_cst_compare (vr->min, CASE_LOW (min_label)) <= 0
&& (CASE_HIGH (max_label) != NULL_TREE
? tree_int_cst_compare (vr->max, CASE_HIGH (max_label)) >= 0
: tree_int_cst_compare (vr->max, CASE_LOW (max_label)) >= 0))
return gimple_switch_label (switch_stmt, 0);
}
return NULL_TREE;
}
if (gassign *assign_stmt = dyn_cast <gassign *> (stmt))
{
value_range new_vr = VR_INITIALIZER;