While building a data dependency graph for loop a ddg edge for some pair
of instructions with inter-loop dependency should be created only if
there is no edge for intra-loop dependency between these instructions.
Creating both of edges leads sometimes to the fact that function
generate_reg_moves creates a redundant register renaming, and some
instruction receives wrong register value from previous iteration.
Overall, this gives a miscompilation.
The add_inter_loop_mem_dep(from,to) function is called only when no
inter-loop "from->to" edge exists, but this function sometimes creates
backward "to->from" edges. This patch prevents these backward edges to
be redundant, it allows to create such edge only when there is no
inter-loop one.
2011-07-20 Roman Zhuykov <zhr...@ispras.ru>
* ddg.c (add_intra_loop_mem_dep): Add new parameter (from_index).
Use it to check whether backward edge is redundant.
(build_intra_loop_deps): Update call to add_intra_loop_mem_dep.
---
gcc/ddg.c | 15 +++++++++------
1 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/gcc/ddg.c b/gcc/ddg.c
index 2bb2cc1..5d0a401 100644
--- a/gcc/ddg.c
+++ b/gcc/ddg.c
@@ -418,7 +418,7 @@ add_intra_loop_mem_dep (ddg_ptr g, ddg_node_ptr from,
ddg_node_ptr to)
/* Given two nodes, analyze their RTL insns and add inter-loop mem deps
to ddg G. */
static void
-add_inter_loop_mem_dep (ddg_ptr g, ddg_node_ptr from, ddg_node_ptr to)
+add_inter_loop_mem_dep (ddg_ptr g, ddg_node_ptr from, ddg_node_ptr to, int
from_index)
{
if (!insns_may_alias_p (from->insn, to->insn))
/* Do not create edge if memory references have disjoint alias sets. */
@@ -442,10 +442,13 @@ add_inter_loop_mem_dep (ddg_ptr g, ddg_node_ptr from,
ddg_node_ptr to)
else if (from->cuid != to->cuid)
{
create_ddg_dep_no_link (g, from, to, ANTI_DEP, MEM_DEP, 1);
- if (DEBUG_INSN_P (from->insn) || DEBUG_INSN_P (to->insn))
- create_ddg_dep_no_link (g, to, from, ANTI_DEP, MEM_DEP, 1);
- else
- create_ddg_dep_no_link (g, to, from, TRUE_DEP, MEM_DEP, 1);
+ if (! TEST_BIT (to->successors, from_index))
+ {
+ if (DEBUG_INSN_P (from->insn) || DEBUG_INSN_P (to->insn))
+ create_ddg_dep_no_link (g, to, from, ANTI_DEP, MEM_DEP, 1);
+ else
+ create_ddg_dep_no_link (g, to, from, TRUE_DEP, MEM_DEP, 1);
+ }
}
}
@@ -511,7 +514,7 @@ build_intra_loop_deps (ddg_ptr g)
/* Don't bother calculating inter-loop dep if an intra-loop
dep
already exists. */
if (! TEST_BIT (dest_node->successors, j))
- add_inter_loop_mem_dep (g, dest_node, j_node);
+ add_inter_loop_mem_dep (g, dest_node, j_node, i);
/* If -fmodulo-sched-allow-regmoves
is set certain anti-dep edges are not created.
It might be that these anti-dep edges are on the
--
Roman Zhuykov
zhr...@ispras.ru
