I have Designed and implemented with the following design for the path
splitting of the loops with conditional IF-THEN-ELSE.
The implementation has gone through the bootstrap for Microblaze target along
DEJA GNU regressions tests and
running the MIBench/EEMBC benchmarks. There is no regression seen in Deja GNU
tests and Deja C++ tests results are
better with the path splitting changes(lesser failures). The Mibench/EEMBC
benchmarks are run and no performance degradation is
seen and the performance improvement in telcom_gsm( Mibench benchmarks) of
9.15% and rgbcmy01_lite(EEMBC
benchmarks) the performance improvement of 9.4% is observed.
Proposal on the below were made earlier on path splitting and the reference is
attached.
https://gcc.gnu.org/ml/gcc/2015-03/msg00057.html
The above gains are achieved because of the constant propagation on conditional
which become much easier with the
Path splitting changes and benefitted with other optimization on tree
representation along with better register allocation.
Because of the better granularity.
I will make the SPEC run and Bootstrap on i386 target Before that I would like
to receive your feedbacks and comments
on design and implementation done. I will send the actual patch with SPEC run
and bootstrap on i386 target after
I receive the feedback on the design and the implementation mentioned in this
mail.
Design changes.
1. The dominators of the block with conditional IF statements say BB1 are found
and the join node of the IF-THEN-ELSE
inside the loops is found on the blocks dominated by the BB1 and are not
successor of BB1 are the join node.
2. The Join node is same as the source of the loops latch basic blocks.
3. If the above conditional in (1) and (2) are found the Join node same as the
source of the Loop latch node is
moved into predecessors and the Join node ( Source of the Loop latch node) is
made empty statement block with only
the phi nodes.
4. In the process of moving the Join node into its predecessors the result of
the phi node in the Join node propagated
with the corresponding phi arguments based on which predecessor it came from
in the Join blocks and move into its predecessors.
5. The Dominator INFO is updated after performing the steps of (1) (2) (3) and
(4).
6. The Join which is same as the source of the Loop latch node is made empty
with only the phi node in the Join node.
7. The implementation is done in Jump threading phase of the machine
independent optimization on tree based
representation. The path splitting is called after the Jump threading
optimization is performed.
The following files are modifed.
a) tree-vrp.c
b) tree-ssa-threadedge.c
c) tree-cfg.c
d) tree-ssa-threadedge.h
e) tree-cfg.h
f) cfghooks.c
The diff is attached along with this mail and pasted below.
Please share your thoughts and feedbacks on the above optimization and the
design and the coding and implementation
done for the given above design.
diff --git a/gcc/cfghooks.c b/gcc/cfghooks.c
index 9faa339..559ca96 100644
--- a/gcc/cfghooks.c
+++ b/gcc/cfghooks.c
@@ -581,7 +581,7 @@ delete_basic_block (basic_block bb)
/* If we remove the header or the latch of a loop, mark the loop for
removal. */
- if (loop->latch == bb
+ if (loop && loop->latch == bb
|| loop->header == bb)
mark_loop_for_removal (loop);
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index aed5254..b25e409 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -1838,6 +1838,64 @@ replace_uses_by (tree name, tree val)
}
}
+void
+gimple_threaded_merge_blocks (basic_block a, basic_block b)
+{
+ gimple_stmt_iterator last, gsi, psi;
+
+ if (dump_file)
+fprintf (dump_file, "Merging blocks %d and %d\n", a->index, b->index);
+
+ /* Remove labels from B and set gimple_bb to A for other statements. */
+ for (gsi = gsi_start_bb (b); !gsi_end_p (gsi);)
+ {
+ gimple stmt = gsi_stmt (gsi);
+ if (glabel *label_stmt = dyn_cast (stmt))
+ {
+ tree label = gimple_label_label (label_stmt);
+ int lp_nr;
+
+ gsi_remove (&gsi, false);
+
+ if (FORCED_LABEL (label))
+ {
+ gimple_stmt_iterator dest_gsi = gsi_start_bb (a);
+ gsi_insert_before (&dest_gsi, stmt, GSI_NEW_STMT);
+ }
+ /* Other user labels keep around in a form of a debug stmt. */
+ else if (!DECL_ARTIFICIAL (label) && MAY_HAVE_DEBUG_STMTS)
+ {
+ gimple dbg = gimple_build_debug_bind (label,
+ integer_zero_node,
+ stmt);
+
+ gimple_debug_bind_reset_value (dbg);
+
+ gsi_insert_before (&gsi, dbg, GSI_SAME_STMT);
+
+ }
+ lp_nr = EH_LANDING_PAD_NR (label);
+ if (lp_nr)
+ {
+
