[v5] tree-ssa-sink: Improve code sinking pass
Commit Message
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.
2023-06-01 Ajit Kumar Agarwal <aagarwa1@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 | 71 ++++++++++++++++++---
3 files changed, 95 insertions(+), 10 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
Comments
On 1 June 2023 09:20:08 CEST, Ajit Agarwal <aagarwa1@linux.ibm.com> wrote:
>Hello All:
>
>This patch improves code sinking pass to sink statements before call to reduce
>register pressure.
>Review comments are incorporated.
Hi Ajit!
I had two comments for v4 that you did not address in v5 or followed up.
thanks,
On 01/06/23 2:06 pm, Bernhard Reutner-Fischer wrote:
> On 1 June 2023 09:20:08 CEST, Ajit Agarwal <aagarwa1@linux.ibm.com> wrote:
>> Hello All:
>>
>> This patch improves code sinking pass to sink statements before call to reduce
>> register pressure.
>> Review comments are incorporated.
>
> Hi Ajit!
>
> I had two comments for v4 that you did not address in v5 or followed up.
> thanks,
Which comments I didn't address. Please let me know.
Thanks & Regards
Ajit
On 6/1/23 11:54 PM, Ajit Agarwal via Gcc-patches wrote:
>
>
> On 01/06/23 2:06 pm, Bernhard Reutner-Fischer wrote:
>> On 1 June 2023 09:20:08 CEST, Ajit Agarwal <aagarwa1@linux.ibm.com> wrote:
>>> Hello All:
>>>
>>> This patch improves code sinking pass to sink statements before call to reduce
>>> register pressure.
>>> Review comments are incorporated.
>>
>> Hi Ajit!
>>
>> I had two comments for v4 that you did not address in v5 or followed up.
>> thanks,
>
> Which comments I didn't address. Please let me know.
I believe he's referring to these two comments:
> + && dominated_by_p (CDI_DOMINATORS, new_best_bb, early_bb))
> + {
> + if (def_use_same_block (use))
> + return best_bb;
> +
> + return new_best_bb;
> + }
> + return best_bb;
> + }
>
Many returns.
I'd have said
&& !def_use_same_block (use)
return new_best_bb;
else
return best_bb;
and rephrase the comment above list of Things to consider accordingly.
I agree with Bernhard's comment that it could be rewritten to be clearer.
Although, the "else" isn't really required. So Bernhard's version would
look like:
if (new_best_bb
&& use
&& new_best_bb != best_bb
&& new_best_bb != early_bb
&& !is_gimple_call (stmt)
&& gsi_end_p (gsi_start_phis (new_best_bb))
&& gimple_bb (use) != early_bb
&& !is_gimple_call (use)
&& dominated_by_p (CDI_POST_DOMINATORS, new_best_bb, gimple_bb (use))
&& dominated_by_p (CDI_DOMINATORS, new_best_bb, early_bb)
&& !def_use_same_block (use))
return new_best_bb;
else
return best_bb;
...or just:
if (new_best_bb
&& use
&& new_best_bb != best_bb
&& new_best_bb != early_bb
&& !is_gimple_call (stmt)
&& gsi_end_p (gsi_start_phis (new_best_bb))
&& gimple_bb (use) != early_bb
&& !is_gimple_call (use)
&& dominated_by_p (CDI_POST_DOMINATORS, new_best_bb, gimple_bb (use))
&& dominated_by_p (CDI_DOMINATORS, new_best_bb, early_bb)
&& !def_use_same_block (use))
return new_best_bb;
return best_bb;
Either works.
Peter
On 23/06/23 7:44 am, Peter Bergner wrote:
> On 6/1/23 11:54 PM, Ajit Agarwal via Gcc-patches wrote:
>>
>>
>> On 01/06/23 2:06 pm, Bernhard Reutner-Fischer wrote:
>>> On 1 June 2023 09:20:08 CEST, Ajit Agarwal <aagarwa1@linux.ibm.com> wrote:
>>>> Hello All:
>>>>
>>>> This patch improves code sinking pass to sink statements before call to reduce
>>>> register pressure.
>>>> Review comments are incorporated.
>>>
>>> Hi Ajit!
>>>
>>> I had two comments for v4 that you did not address in v5 or followed up.
>>> thanks,
>>
>> Which comments I didn't address. Please let me know.
>
> I believe he's referring to these two comments:
>
> > + && dominated_by_p (CDI_DOMINATORS, new_best_bb, early_bb))
> > + {
> > + if (def_use_same_block (use))
> > + return best_bb;
> > +
> > + return new_best_bb;
> > + }
> > + return best_bb;
> > + }
> >
>
> Many returns.
> I'd have said
> && !def_use_same_block (use)
> return new_best_bb;
> else
> return best_bb;
>
> and rephrase the comment above list of Things to consider accordingly.
>
>
> I agree with Bernhard's comment that it could be rewritten to be clearer.
> Although, the "else" isn't really required. So Bernhard's version would
> look like:
>
> if (new_best_bb
> && use
> && new_best_bb != best_bb
> && new_best_bb != early_bb
> && !is_gimple_call (stmt)
> && gsi_end_p (gsi_start_phis (new_best_bb))
> && gimple_bb (use) != early_bb
> && !is_gimple_call (use)
> && dominated_by_p (CDI_POST_DOMINATORS, new_best_bb, gimple_bb (use))
> && dominated_by_p (CDI_DOMINATORS, new_best_bb, early_bb)
> && !def_use_same_block (use))
> return new_best_bb;
> else
> return best_bb;
>
> ...or just:
>
> if (new_best_bb
> && use
> && new_best_bb != best_bb
> && new_best_bb != early_bb
> && !is_gimple_call (stmt)
> && gsi_end_p (gsi_start_phis (new_best_bb))
> && gimple_bb (use) != early_bb
> && !is_gimple_call (use)
> && dominated_by_p (CDI_POST_DOMINATORS, new_best_bb, gimple_bb (use))
> && dominated_by_p (CDI_DOMINATORS, new_best_bb, early_bb)
> && !def_use_same_block (use))
> return new_best_bb;
>
> return best_bb;
>
>
> Either works.
Thanks Peter. I will incorporate and send the new version of the patch.
>
>
> Peter
>
new file mode 100644
@@ -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 } } */
new file mode 100644
@@ -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 } } */
@@ -171,9 +171,28 @@ nearest_common_dominator_of_uses (def_operand_p def_p, bool *debug_stmts)
return commondom;
}
+/* Return TRUE if immediate uses of the defs in
+ STMT occur in the same block as STMT, FALSE otherwise. */
+
+static bool
+def_use_same_block (gimple *stmt)
+{
+ def_operand_p def;
+ ssa_op_iter iter;
+
+ FOR_EACH_SSA_DEF_OPERAND (def, stmt, iter, SSA_OP_DEF)
+ {
+ gimple *def_stmt = SSA_NAME_DEF_STMT (DEF_FROM_PTR (def));
+ if ((gimple_bb (def_stmt) == gimple_bb (stmt)))
+ return true;
+ }
+ return false;
+}
+
/* 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.
@@ -190,7 +209,8 @@ 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;
@@ -237,7 +257,40 @@ select_best_block (basic_block early_bb,
/* If result of comparsion is unknown, prefer EARLY_BB.
Thus use !(...>=..) rather than (...<...) */
&& !(best_bb->count * 100 >= early_bb->count * threshold))
- return best_bb;
+ {
+ basic_block new_best_bb = get_immediate_dominator (CDI_DOMINATORS, best_bb);
+ /* Return best_bb if def and use are in same block otherwise new_best_bb.
+
+ Things to consider:
+
+ new_best_bb is not equal to best_bb and early_bb.
+
+ stmt is not call.
+
+ new_best_bb doesnt have any phis.
+
+ use basic block is not equal to early_bb.
+
+ use basic block post dominates to new_best_bb.
+
+ new_best_bb dominates early_bb. */
+ if (new_best_bb && use
+ && new_best_bb != best_bb
+ && new_best_bb != early_bb
+ && !is_gimple_call (stmt)
+ && gsi_end_p (gsi_start_phis (new_best_bb))
+ && gimple_bb (use) != early_bb
+ && !is_gimple_call (use)
+ && dominated_by_p (CDI_POST_DOMINATORS, new_best_bb, gimple_bb (use))
+ && dominated_by_p (CDI_DOMINATORS, new_best_bb, early_bb))
+ {
+ if (def_use_same_block (use))
+ return best_bb;
+
+ return new_best_bb;
+ }
+ return best_bb;
+ }
/* No better block found, so return EARLY_BB, which happens to be the
statement's original block. */
@@ -439,7 +492,7 @@ 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 +509,17 @@ 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 +531,7 @@ 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;