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-------- Forwarded Message --------
Subject: [PATCH v8] tree-ssa-sink: Improve code sinking pass.
Date: Tue, 18 Jul 2023 19:03:37 +0530
From: Ajit Agarwal <aagar...@linux.ibm.com>
To: gcc-patches <gcc-patches@gcc.gnu.org>
CC: Richard Biener <richard.guent...@gmail.com>, Jeff Law
<jeffreya...@gmail.com>, Segher Boessenkool <seg...@kernel.crashing.org>, Peter
Bergner <berg...@linux.ibm.com>
Hello All:
This patch improves code sinking pass to sink statements before call to reduce
register pressure.
Review comments are incorporated.
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.
2023-07-18 Ajit Kumar Agarwal <aagar...@linux.ibm.com>
gcc/ChangeLog:
PR tree-optimization/81953
* tree-ssa-sink.cc (statement_sink_location): Move statements before
calls.
(def_use_same_block): New function.
(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 testcase.
* gcc.dg/tree-ssa/ssa-sink-21.c: New testcase.
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c | 15 ++++++
gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c | 19 +++++++
gcc/tree-ssa-sink.cc | 59 ++++++++++++---------
3 files changed, 67 insertions(+), 26 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.c
new file mode 100644
index 00000000000..d3b79ca5803
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-20.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-21.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
new file mode 100644
index 00000000000..84e7938c54f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.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 b1ba7a2ad6c..e7190323abe 100644
--- a/gcc/tree-ssa-sink.cc
+++ b/gcc/tree-ssa-sink.cc
@@ -173,7 +173,8 @@ 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.
@@ -190,11 +191,22 @@ nearest_common_dominator_of_uses (def_operand_p def_p,
bool *debug_stmts)
static basic_block
select_best_block (basic_block early_bb,
basic_block late_bb,
- gimple *stmt)
+ gimple *stmt,
+ gimple *use)
{
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)
{
@@ -203,34 +215,31 @@ select_best_block (basic_block early_bb,
if (bb_loop_depth (temp_bb) < bb_loop_depth (best_bb))
best_bb = temp_bb;
+ /* Placing a statement before a setjmp-like function would be invalid
+ (it cannot be reevaluated when execution follows an abnormal edge).
+ If we selected a block with abnormal predecessors, just punt. */
+ if (bb_has_abnormal_pred (temp_bb))
+ return early_bb;
+
+ /* if we have temp_bb post dominated by use block block then immediate
+ * dominator would be our best block. */
+ if (use
+ && bb_loop_depth(temp_bb) == bb_loop_depth (early_bb)
+ && !(temp_bb->count * 100 >= early_bb->count * threshold)
+ && dominated_by_p (CDI_POST_DOMINATORS, temp_bb, gimple_bb (use)))
+ 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);
}
- /* Placing a statement before a setjmp-like function would be invalid
- (it cannot be reevaluated when execution follows an abnormal edge).
- If we selected a block with abnormal predecessors, just punt. */
- if (bb_has_abnormal_pred (best_bb))
- return early_bb;
-
/* If we found a shallower loop nest, then we always consider that
a win. This will always give us the most control dependent block
within that loop nest. */
if (bb_loop_depth (best_bb) < bb_loop_depth (early_bb))
return best_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)
@@ -439,7 +448,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
if (!dominated_by_p (CDI_DOMINATORS, commondom, frombb))
return false;
- commondom = select_best_block (frombb, commondom, stmt);
+ commondom = select_best_block (frombb, commondom, stmt, NULL);
if (commondom == frombb)
return false;
@@ -456,19 +465,17 @@ statement_sink_location (gimple *stmt, basic_block frombb,
continue;
break;
}
+
use = USE_STMT (one_use);
if (gimple_code (use) != GIMPLE_PHI)
{
- sinkbb = select_best_block (frombb, gimple_bb (use), stmt);
+ sinkbb = select_best_block (frombb, gimple_bb (use), stmt, use);
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;
}
@@ -480,7 +487,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
if (!sinkbb)
return false;
- sinkbb = select_best_block (frombb, sinkbb, stmt);
+ sinkbb = select_best_block (frombb, sinkbb, stmt, NULL);
if (!sinkbb || sinkbb == frombb)
return false;
--
2.39.3
