This patch improves code sinking pass to sink statements before call to reduce
register pressure.
Review comments are incorporated. Synced and modified with latest trunk sources.
For example :
void bar();
int j;
void foo(int a, int b, int c, int d, int e, int f)
{
int l;
l = a + b + c + d +e + f;
if (a != 5)
{
bar();
j = l;
}
}
Code Sinking does the following:
void bar();
int j;
void foo(int a, int b, int c, int d, int e, int f)
{
int l;
if (a != 5)
{
l = a + b + c + d +e + f;
bar();
j = l;
}
}
Bootstrapped regtested on powerpc64-linux-gnu.
Thanks & Regards
Ajit
tree-ssa-sink: Improve code sinking pass
Currently, code sinking will sink code after function calls. This increases
register pressure for callee-saved registers. The following patch improves
code sinking by placing the sunk code before calls in the use block or in
the immediate dominator of the use blocks.
2023-10-12 Ajit Kumar Agarwal <[email protected]>
gcc/ChangeLog:
PR tree-optimization/81953
* tree-ssa-sink.cc (statement_sink_location): Move statements before
calls.
(select_best_block): Add heuristics to select the best blocks in the
immediate post dominator.
gcc/testsuite/ChangeLog:
PR tree-optimization/81953
* gcc.dg/tree-ssa/ssa-sink-20.c: New test.
* gcc.dg/tree-ssa/ssa-sink-21.c: New test.
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c | 15 ++++++++
gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c | 19 ++++++++++
gcc/tree-ssa-sink.cc | 39 ++++++++++++---------
3 files changed, 56 insertions(+), 17 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
new file mode 100644
index 00000000000..d3b79ca5803
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-sink-stats" } */
+void bar();
+int j;
+void foo(int a, int b, int c, int d, int e, int f)
+{
+ int l;
+ l = a + b + c + d +e + f;
+ if (a != 5)
+ {
+ bar();
+ j = l;
+ }
+}
+/* { dg-final { scan-tree-dump
{l_12\s+=\s+_4\s+\+\s+f_11\(D\);\n\s+bar\s+\(\)} sink1 } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
new file mode 100644
index 00000000000..84e7938c54f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-sink-stats" } */
+void bar();
+int j, x;
+void foo(int a, int b, int c, int d, int e, int f)
+{
+ int l;
+ l = a + b + c + d +e + f;
+ if (a != 5)
+ {
+ bar();
+ if (b != 3)
+ x = 3;
+ else
+ x = 5;
+ j = l;
+ }
+}
+/* { dg-final { scan-tree-dump
{l_13\s+=\s+_4\s+\+\s+f_12\(D\);\n\s+bar\s+\(\)} sink1 } } */
diff --git a/gcc/tree-ssa-sink.cc b/gcc/tree-ssa-sink.cc
index a360c5cdd6e..95298bc8402 100644
--- a/gcc/tree-ssa-sink.cc
+++ b/gcc/tree-ssa-sink.cc
@@ -174,7 +174,8 @@ nearest_common_dominator_of_uses (def_operand_p def_p, bool
*debug_stmts)
/* Given EARLY_BB and LATE_BB, two blocks in a path through the dominator
tree, return the best basic block between them (inclusive) to place
- statements.
+ statements. The best basic block should be an immediate dominator of
+ best basic block if the use stmt is after the call.
We want the most control dependent block in the shallowest loop nest.
@@ -196,6 +197,16 @@ select_best_block (basic_block early_bb,
basic_block best_bb = late_bb;
basic_block temp_bb = late_bb;
int threshold;
+ /* Get the sinking threshold. If the statement to be moved has memory
+ operands, then increase the threshold by 7% as those are even more
+ profitable to avoid, clamping at 100%. */
+ threshold = param_sink_frequency_threshold;
+ if (gimple_vuse (stmt) || gimple_vdef (stmt))
+ {
+ threshold += 7;
+ if (threshold > 100)
+ threshold = 100;
+ }
while (temp_bb != early_bb)
{
@@ -204,6 +215,14 @@ select_best_block (basic_block early_bb,
if (bb_loop_depth (temp_bb) < bb_loop_depth (best_bb))
best_bb = temp_bb;
+ /* if we have temp_bb post dominated by use block block then immediate
+ * dominator would be our best block. */
+ if (!gimple_vuse (stmt)
+ && bb_loop_depth (temp_bb) == bb_loop_depth (early_bb)
+ && !(temp_bb->count * 100 >= early_bb->count * threshold)
+ && dominated_by_p (CDI_DOMINATORS, late_bb, temp_bb))
+ best_bb = temp_bb;
+
/* Walk up the dominator tree, hopefully we'll find a shallower
loop nest. */
temp_bb = get_immediate_dominator (CDI_DOMINATORS, temp_bb);
@@ -233,17 +252,6 @@ select_best_block (basic_block early_bb,
&& !dominated_by_p (CDI_DOMINATORS, best_bb->loop_father->latch,
best_bb))
return early_bb;
- /* Get the sinking threshold. If the statement to be moved has memory
- operands, then increase the threshold by 7% as those are even more
- profitable to avoid, clamping at 100%. */
- threshold = param_sink_frequency_threshold;
- if (gimple_vuse (stmt) || gimple_vdef (stmt))
- {
- threshold += 7;
- if (threshold > 100)
- threshold = 100;
- }
-
/* If BEST_BB is at the same nesting level, then require it to have
significantly lower execution frequency to avoid gratuitous movement. */
if (bb_loop_depth (best_bb) == bb_loop_depth (early_bb)
@@ -430,6 +438,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
continue;
break;
}
+
use = USE_STMT (one_use);
if (gimple_code (use) != GIMPLE_PHI)
@@ -439,10 +448,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
if (sinkbb == frombb)
return false;
- if (sinkbb == gimple_bb (use))
- *togsi = gsi_for_stmt (use);
- else
- *togsi = gsi_after_labels (sinkbb);
+ *togsi = gsi_after_labels (sinkbb);
return true;
}
@@ -825,7 +831,6 @@ pass_sink_code::execute (function *fun)
mark_dfs_back_edges (fun);
memset (&sink_stats, 0, sizeof (sink_stats));
calculate_dominance_info (CDI_DOMINATORS);
-
virtual_operand_live vop_live;
int *rpo = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
--
2.39.3
