That's a weird function in predicate analysis that currently looks like
/* Return true if BB1 is postdominating BB2 and BB1 is not a loop exit
bb. The loop exit bb check is simple and does not cover all cases. */
static bool
is_non_loop_exit_postdominating (basic_block bb1, basic_block bb2)
{
if (!dominated_by_p (CDI_POST_DOMINATORS, bb2, bb1))
return false;
if (single_pred_p (bb1) && !single_succ_p (bb2))
return false;
return true;
}
One can refactor this to
return (dominated_by_p (CDI_POST_DOMINATORS, bb2, bb1)
&& !(single_pred_p (bb1) && !single_succ_p (bb2)));
Notable is that the comment refers to BB1 with respect to a loop
exit but the test seems to be written with an exit edge bb1 -> bb2
in mind. From the three callers only a single one is guaranteed
to have bb1 and bb2 connected directly with an edge.
The patch now introduces a is_loop_exit function and inlines
the post-dominance check which makes the find_control_equiv_block
case simpler because the post-dominance check can be elided.
It also avoids the double negation in compute_control_dep_chain
and makes it obvious this is the case where we do look at an edge.
For the main is_use_guarded API I chose to elide the loop exit
test, if the use block post-dominates the definition block of the
PHI node the use is always unconditional. I don't quite understand
the loop exit special-casing of the remaining two uses though.
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
The code is this way since the original r0-99656-g34f97b9407c6a3
so I'm not hoping for any insights ... :/
* gimple-predicate-analysis.cc (is_loop_exit): Split out
from ...
(is_non_loop_exit_postdominating): ... here. Remove after
inlining ...
(find_control_equiv_block): ... here.
(compute_control_dep_chain): ... and here.
(predicate::is_use_guarded): Do not excempt loop exits
from short-cutting the case of the use post-dominating the
PHI definition.
---
gcc/gimple-predicate-analysis.cc | 22 ++++++++--------------
1 file changed, 8 insertions(+), 14 deletions(-)
diff --git a/gcc/gimple-predicate-analysis.cc b/gcc/gimple-predicate-analysis.cc
index d1b0d1283dc..4cf05951ec7 100644
--- a/gcc/gimple-predicate-analysis.cc
+++ b/gcc/gimple-predicate-analysis.cc
@@ -46,19 +46,12 @@
#define DEBUG_PREDICATE_ANALYZER 1
-/* Return true if BB1 is postdominating BB2 and BB1 is not a loop exit
- bb. The loop exit bb check is simple and does not cover all cases. */
+/* Return true if, when BB1 is postdominating BB2, BB1 is a loop exit. */
static bool
-is_non_loop_exit_postdominating (basic_block bb1, basic_block bb2)
+is_loop_exit (basic_block bb2, basic_block bb1)
{
- if (!dominated_by_p (CDI_POST_DOMINATORS, bb2, bb1))
- return false;
-
- if (single_pred_p (bb1) && !single_succ_p (bb2))
- return false;
-
- return true;
+ return single_pred_p (bb1) && !single_succ_p (bb2);
}
/* Find BB's closest postdominator that is its control equivalent (i.e.,
@@ -70,7 +63,7 @@ find_control_equiv_block (basic_block bb)
basic_block pdom = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
/* Skip the postdominating bb that is also a loop exit. */
- if (!is_non_loop_exit_postdominating (pdom, bb))
+ if (is_loop_exit (bb, pdom))
return NULL;
/* If the postdominator is dominated by BB, return it. */
@@ -1112,10 +1105,11 @@ compute_control_dep_chain (basic_block dom_bb,
const_basic_block dep_bb,
if (e->flags & (EDGE_FAKE | EDGE_ABNORMAL))
continue;
- basic_block cd_bb = e->dest;
cur_cd_chain.safe_push (e);
- while (!is_non_loop_exit_postdominating (cd_bb, dom_bb))
+ while (!dominated_by_p (CDI_POST_DOMINATORS, e->src, e->dest)
+ || is_loop_exit (e->src, e->dest))
{
+ basic_block cd_bb = e->dest;
if (cd_bb == dep_bb)
{
/* Found a direct control dependence. */
@@ -1885,7 +1879,7 @@ predicate::is_use_guarded (gimple *use_stmt, basic_block
use_bb,
in the same bb. */
predicate use_preds (def_bb, use_bb, m_eval);
- if (is_non_loop_exit_postdominating (use_bb, def_bb))
+ if (dominated_by_p (CDI_POST_DOMINATORS, def_bb, use_bb))
{
if (is_empty ())
{
--
2.35.3
