On Mon, 24 Jun 2013, Richard Biener wrote:
>
> The following fixes a long-standing bug in tree if-conversion.
> The transform phase relies on being able to extract edge predicates
> by simply using the predicate under which its source block is
> executed. That obviously isn't the correct one if the source
> block ends in a condition itself. Thus the following patch
> verifies that each predecessor edge of blocks we will if-convert
> is non-critical.
>
> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
... to pick up where I left.
That didn't work out, we need to handle the case of one edge being
non-critical only to not regress. I've dug in history where all the
strange existing tests come from - and they are all for bugs
exhibiting this very same problem, just they paper over it in various
interesting ways.
So the following removes all of them, re-doing the above fix in
a less conservative way.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2013-08-27 Richard Biener <rguent...@suse.de>
PR tree-optimization/57521
* tree-if-conv.c (if_convertible_bb_p): Verify that at least
one edge is non-critical.
(find_phi_replacement_condition): Make sure to use a non-critical
edge. Cleanup and remove old bug workarounds.
(bb_postdominates_preds): Remove.
(if_convertible_loop_p_1): Do not compute post-dominators.
(combine_blocks): Do not free post-dominators.
(main_tree_if_conversion): Likewise.
(pass_data_if_conversion): Add TODO_verify_ssa.
* gcc.dg/torture/pr57521.c: New testcase.
Index: gcc/tree-if-conv.c
===================================================================
*** gcc/tree-if-conv.c (revision 202017)
--- gcc/tree-if-conv.c (working copy)
*************** if_convertible_stmt_p (gimple stmt, vec<
*** 797,816 ****
return true;
}
- /* Return true when BB post-dominates all its predecessors. */
-
- static bool
- bb_postdominates_preds (basic_block bb)
- {
- unsigned i;
-
- for (i = 0; i < EDGE_COUNT (bb->preds); i++)
- if (!dominated_by_p (CDI_POST_DOMINATORS, EDGE_PRED (bb, i)->src, bb))
- return false;
-
- return true;
- }
-
/* Return true when BB is if-convertible. This routine does not check
basic block's statements and phis.
--- 797,802 ----
*************** if_convertible_bb_p (struct loop *loop,
*** 868,877 ****
return false;
}
! if (EDGE_COUNT (bb->preds) == 2
! && bb != loop->header
! && !bb_postdominates_preds (bb))
! return false;
return true;
}
--- 854,876 ----
return false;
}
! /* At least one incoming edge has to be non-critical as otherwise edge
! predicates are not equal to basic-block predicates of the edge
! source. */
! if (EDGE_COUNT (bb->preds) > 1
! && bb != loop->header)
! {
! bool found = false;
! FOR_EACH_EDGE (e, ei, bb->preds)
! if (EDGE_COUNT (e->src->succs) == 1)
! found = true;
! if (!found)
! {
! if (dump_file && (dump_flags & TDF_DETAILS))
! fprintf (dump_file, "only critical predecessors\n");
! return false;
! }
! }
return true;
}
*************** if_convertible_loop_p_1 (struct loop *lo
*** 1084,1090 ****
return false;
calculate_dominance_info (CDI_DOMINATORS);
- calculate_dominance_info (CDI_POST_DOMINATORS);
/* Allow statements that can be handled during if-conversion. */
ifc_bbs = get_loop_body_in_if_conv_order (loop);
--- 1083,1088 ----
*************** if_convertible_loop_p (struct loop *loop
*** 1220,1227 ****
if-conversion. */
static basic_block
! find_phi_replacement_condition (struct loop *loop,
! basic_block bb, tree *cond,
gimple_stmt_iterator *gsi)
{
edge first_edge, second_edge;
--- 1218,1224 ----
if-conversion. */
static basic_block
! find_phi_replacement_condition (basic_block bb, tree *cond,
gimple_stmt_iterator *gsi)
{
edge first_edge, second_edge;
*************** find_phi_replacement_condition (struct l
*** 1231,1264 ****
first_edge = EDGE_PRED (bb, 0);
second_edge = EDGE_PRED (bb, 1);
! /* Use condition based on following criteria:
! 1)
! S1: x = !c ? a : b;
!
! S2: x = c ? b : a;
!
! S2 is preferred over S1. Make 'b' first_bb and use its condition.
!
! 2) Do not make loop header first_bb.
!
! 3)
! S1: x = !(c == d)? a : b;
!
! S21: t1 = c == d;
! S22: x = t1 ? b : a;
!
! S3: x = (c == d) ? b : a;
!
! S3 is preferred over S1 and S2*, Make 'b' first_bb and use
! its condition.
!
! 4) If pred B is dominated by pred A then use pred B's condition.
! See PR23115. */
!
! /* Select condition that is not TRUTH_NOT_EXPR. */
tmp_cond = bb_predicate (first_edge->src);
gcc_assert (tmp_cond);
-
if (TREE_CODE (tmp_cond) == TRUTH_NOT_EXPR)
{
edge tmp_edge;
--- 1228,1237 ----
first_edge = EDGE_PRED (bb, 0);
second_edge = EDGE_PRED (bb, 1);
! /* Prefer an edge with a not negated predicate.
! ??? That's a very weak cost model. */
tmp_cond = bb_predicate (first_edge->src);
gcc_assert (tmp_cond);
if (TREE_CODE (tmp_cond) == TRUTH_NOT_EXPR)
{
edge tmp_edge;
*************** find_phi_replacement_condition (struct l
*** 1268,1278 ****
second_edge = tmp_edge;
}
! /* Check if FIRST_BB is loop header or not and make sure that
! FIRST_BB does not dominate SECOND_BB. */
! if (first_edge->src == loop->header
! || dominated_by_p (CDI_DOMINATORS,
! second_edge->src, first_edge->src))
{
*cond = bb_predicate (second_edge->src);
--- 1241,1249 ----
second_edge = tmp_edge;
}
! /* Check if the edge we take the condition from is not critical.
! We know that at least one non-critical edge exists. */
! if (EDGE_COUNT (first_edge->src->succs) > 1)
{
*cond = bb_predicate (second_edge->src);
*************** predicate_scalar_phi (gimple phi, tree c
*** 1347,1355 ****
arg_1 = gimple_phi_arg_def (phi, 1);
}
- gcc_checking_assert (bb == bb->loop_father->header
- || bb_postdominates_preds (bb));
-
/* Build new RHS using selected condition and arguments. */
rhs = fold_build_cond_expr (TREE_TYPE (res), unshare_expr (cond),
arg_0, arg_1);
--- 1318,1323 ----
*************** predicate_all_scalar_phis (struct loop *
*** 1395,1401 ****
/* BB has two predecessors. Using predecessor's aux field, set
appropriate condition for the PHI node replacement. */
gsi = gsi_after_labels (bb);
! true_bb = find_phi_replacement_condition (loop, bb, &cond, &gsi);
while (!gsi_end_p (phi_gsi))
{
--- 1363,1369 ----
/* BB has two predecessors. Using predecessor's aux field, set
appropriate condition for the PHI node replacement. */
gsi = gsi_after_labels (bb);
! true_bb = find_phi_replacement_condition (bb, &cond, &gsi);
while (!gsi_end_p (phi_gsi))
{
*************** combine_blocks (struct loop *loop)
*** 1765,1773 ****
free (ifc_bbs);
ifc_bbs = NULL;
-
- /* Post-dominators are corrupt now. */
- free_dominance_info (CDI_POST_DOMINATORS);
}
/* If-convert LOOP when it is legal. For the moment this pass has no
--- 1733,1738 ----
*************** main_tree_if_conversion (void)
*** 1830,1837 ****
if (changed && flag_tree_loop_if_convert_stores)
todo |= TODO_update_ssa_only_virtuals;
- free_dominance_info (CDI_POST_DOMINATORS);
-
#ifdef ENABLE_CHECKING
{
basic_block bb;
--- 1795,1800 ----
*************** const pass_data pass_data_if_conversion
*** 1867,1873 ****
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
! ( TODO_verify_stmts | TODO_verify_flow ), /* todo_flags_finish */
};
class pass_if_conversion : public gimple_opt_pass
--- 1830,1837 ----
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
! ( TODO_verify_stmts | TODO_verify_flow
! | TODO_verify_ssa ), /* todo_flags_finish */
};
class pass_if_conversion : public gimple_opt_pass
Index: gcc/testsuite/gcc.dg/torture/pr57521.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr57521.c (revision 0)
--- gcc/testsuite/gcc.dg/torture/pr57521.c (working copy)
***************
*** 0 ****
--- 1,51 ----
+ /* { dg-do run } */
+ /* { dg-options "-ftree-loop-if-convert" } */
+
+ void abort (void);
+
+ int a, b, c, d, o = 1, p;
+ short e;
+
+ int
+ fn1 (int * p1)
+ {
+ int f, g, h, j = 0, k = 0, l = 0;
+ unsigned int i;
+ int *m[1] = { &l };
+ for (; b >= 0; b--)
+ {
+ if (*p1)
+ if (j >= 0)
+ {
+ int n = 1;
+ e = 1;
+ h = a ? a : 1 % n;
+ g = h > 0 ? 0 : h + 1;
+ k = c + g;
+ }
+ else
+ continue;
+ else
+ {
+
+ f = d > 0 ? 0 : d + 1;
+ i = f;
+ j = 1 + i;
+ }
+ l++;
+ }
+ return k;
+ }
+
+ int
+ main ()
+ {
+ for (;; p++)
+ {
+ fn1 (&o);
+ break;
+ }
+ if (e != 1)
+ abort ();
+ return 0;
+ }
