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loop-ch improvements, part 5

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Currently loop-ch skips all do-while loops.  But when loop is not do-while
in addition to original goal of turining it to do-while it can do additional
things:
 1) move out loop invariant computations
 2) duplicate loop invariant conditionals and eliminate them in loop body.
 3) prove that some exits are always true in first iteration
    and can be skipped

Most of time 1 can be done by lim (exception is when the invariant computation
is conditional). For 2 we however don't really have other place doing it except
for loop unswitching that is more expensive (it will duplicate the loop and
then optimize out one path to non-loop).
3 can be done by loop peeling but it is also more expensive by duplicating full
loop body.

This patch improves heuristics by not giving up on do-while loops and trying
to find sequence of BBs to duplicate to obtain one of goals:
 - turn loop to do-while
 - eliminate invariant conditional in loop body
 - do partial "peeling" as long as code optimizes enough so this does not
   increase code size.

Bootstrapped/regtested x86_64-linux, OK?

gcc/ChangeLog:

	* tree-ssa-loop-ch.cc (enum ch_decision): New enum.
	(should_duplicate_loop_header_p): Return info on profitability.
	(do_while_loop_p): Watch for constant conditionals.
	(update_profile_after_ch): Do not sanity check that all
	static exits are taken.
	(ch_base::copy_headers): Run on all loops.
	(pass_ch::process_loop_p): Improve heuristics by handling also
	do_while loop and duplicating shortest sequence containing all
	winning blocks.

gcc/testsuite/ChangeLog:

	* gcc.dg/loop-unswitch-17.c: Disable ch.
	* gcc.dg/pr103079.c: Disable ch.
	* gcc.dg/tree-ssa/copy-headers-7.c: Update so ch behaves
	as expected.
	* gcc.dg/tree-ssa/copy-headers.c: Update template.
	* gcc.dg/tree-ssa/copy-headers-9.c: New test.
This commit is contained in:
Jan Hubicka 2023-07-21 14:54:23 +02:00
parent 8cbdb2e4d6
commit 65ff4a45b1
6 changed files with 136 additions and 40 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
gcc/testsuite/gcc.dg/loop-unswitch-17.c
View file

@ -1,5 +1,5 @@
/* { dg-do compile } */
/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-optimized" } */
/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-optimized -fno-tree-ch" } */
int foo (int a)
{

2
gcc/testsuite/gcc.dg/pr103079.c
View file

@ -1,5 +1,5 @@
/* { dg-do compile } */
/* { dg-options "-Os -fdump-tree-vrp2" } */
/* { dg-options "-Os -fdump-tree-vrp2 -fno-tree-ch" } */
int a, b = -2;
int main() {

3
gcc/testsuite/gcc.dg/tree-ssa/copy-headers-7.c
View file

@ -4,7 +4,7 @@
int is_sorted(int *a, int n, int m, int k)
{
if (k > 0)
for (int i = 0; i < n - 1 && m && k > i; i++)
for (int i = 0; k > i && m && i < n - 1 ; i++)
if (a[i] > a[i + 1])
return 0;
return 1;
@ -17,5 +17,4 @@ int is_sorted(int *a, int n, int m, int k)
/* { dg-final { scan-tree-dump-times "Conditional combines static and invariant" 0 "ch2" } } */
/* { dg-final { scan-tree-dump-times "Will elliminate invariant exit" 1 "ch2" } } */
/* { dg-final { scan-tree-dump-times "Will eliminate peeled conditional" 1 "ch2" } } */
/* { dg-final { scan-tree-dump-times "Not duplicating bb .: condition based on non-IV loop variant." 1 "ch2" } } */
/* { dg-final { scan-tree-dump-times "Will duplicate bb" 3 "ch2" } } */

20
gcc/testsuite/gcc.dg/tree-ssa/copy-headers-9.c Normal file
View file

@ -0,0 +1,20 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-ch-details" } */
int a[100];
void test (int m, int n)
{
int i = 0;
do
{
if (m)
break;
i++;
a[i]=0;
}
while (i<10);
}
/* { dg-final { scan-tree-dump-times "Duplicating bb . is a win" 1 "ch2" } } */
/* { dg-final { scan-tree-dump-times "May duplicate bb" 1 "ch2" } } */
/* { dg-final { scan-tree-dump-times "Duplicating additional BB to obtain do-while loop" 1 "ch2" } } */
/* { dg-final { scan-tree-dump-times "Will duplicate bb" 2 "ch2" } } */
/* { dg-final { scan-tree-dump "is now do-while loop" "ch2" } } */

2
gcc/testsuite/gcc.dg/tree-ssa/copy-headers.c
View file

@ -12,4 +12,4 @@ void bla (void)
}
/* There should be a header duplicated. */
/* { dg-final { scan-tree-dump-times "Duplicating header" 1 "ch2"} } */
/* { dg-final { scan-tree-dump-times "Duplicating header of the" 1 "ch2"} } */

147
gcc/tree-ssa-loop-ch.cc
View file

@ -168,11 +168,28 @@ loop_combined_static_and_iv_p (class loop *loop,
return gimple_uid (SSA_NAME_DEF_STMT (op)) & 4;
}
/* Decision about posibility of copying a given header. */
enum ch_decision
{
/* We do not want to copy this header. */
ch_impossible,
/* We can copy it if it enables wins. */
ch_possible,
/* We can "cop" it if it enables wins and doing
so will introduce no new code. */
ch_possible_zero_cost,
/* We want to copy. */
ch_win,
/* We want to copy and we will eliminate loop exit. */
ch_win_invariant_exit
};
/* Check whether we should duplicate HEADER of LOOP. At most *LIMIT
instructions should be duplicated, limit is decreased by the actual
amount. */
static bool
static ch_decision
should_duplicate_loop_header_p (basic_block header, class loop *loop,
gimple_ranger *ranger,
int *limit,
@ -190,7 +207,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
fprintf (dump_file,
" Not duplicating bb %i: it is single succ.\n",
header->index);
return false;
return ch_impossible;
}
if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest)
@ -200,7 +217,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
fprintf (dump_file,
" Not duplicating bb %i: both successors are in loop.\n",
loop->num);
return false;
return ch_impossible;
}
/* If this is not the original loop header, we want it to have just
@ -211,7 +228,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
fprintf (dump_file,
" Not duplicating bb %i: it has mutiple predecestors.\n",
header->index);
return false;
return ch_impossible;
}
gcond *last = safe_dyn_cast <gcond *> (*gsi_last_bb (header));
@ -221,7 +238,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
fprintf (dump_file,
" Not duplicating bb %i: it does not end by conditional.\n",
header->index);
return false;
return ch_impossible;
}
path_range_query *query = NULL;
@ -233,6 +250,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
query, psi.phi ());
gimple_set_uid (psi.phi (), static_p ? 2 : 0);
}
bool code_size_cost = false;
/* Count number of instructions and punt on calls.
Populate stmts INV flag to later apply heuristics to the
@ -268,7 +286,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
header->index);
if (query)
delete query;
return false;
return ch_impossible;
}
/* Classify the stmt is invariant in the loop. */
@ -343,6 +361,8 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
int insns = estimate_num_insns (last, &eni_size_weights);
*limit -= insns;
if (insns)
code_size_cost = true;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
" Acconting stmt as %i insns\n", insns);
@ -354,7 +374,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
header->index);
if (query)
delete query;
return false;
return ch_impossible;
}
}
@ -403,7 +423,7 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
" Conditional combines static and invariant op.\n");
return true;
return ch_win;
}
edge static_exit = static_loop_exit (loop, header, *ranger, query);
@ -435,11 +455,16 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
invariant_exits->add (e);
}
}
return true;
return ch_win_invariant_exit;
}
/* If the static exit fully optimize out, it is win to "duplicate"
it.
TODO: Even if duplication costs some size we may opt to do so in case
exit probability is significant enough (do partial peeling). */
if (static_exit)
return true;
return code_size_cost ? ch_possible_zero_cost : ch_win;
/* We was not able to prove that conditional will be eliminated. */
int insns = estimate_num_insns (last, &eni_size_weights);
@ -453,19 +478,10 @@ should_duplicate_loop_header_p (basic_block header, class loop *loop,
fprintf (dump_file,
" Not duplicating bb %i contains too many insns.\n",
header->index);
return false;
return ch_impossible;
}
if (header != loop->header)
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
" Not duplicating bb %i: condition based on non-IV loop"
" variant.\n", header->index);
return false;
}
return true;
return ch_possible;
}
/* Checks whether LOOP is a do-while style loop. */
@ -496,10 +512,11 @@ do_while_loop_p (class loop *loop)
"predecessors.\n", loop->num);
return false;
}
basic_block pred = single_pred (loop->latch);
/* If the latch predecessor doesn't exit the loop, it is not a
do-while loop. */
if (!loop_exits_from_bb_p (loop, single_pred (loop->latch)))
if (!loop_exits_from_bb_p (loop, pred))
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
@ -507,6 +524,18 @@ do_while_loop_p (class loop *loop)
"does not exit loop.\n", loop->num);
return false;
}
gcond *last = safe_dyn_cast <gcond *> (*gsi_last_bb (pred));
if (last
&& (gimple_cond_lhs (last) == boolean_false_node
|| gimple_cond_lhs (last) == boolean_true_node)
&& gimple_cond_rhs (last) == boolean_false_node)
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
"Loop %i is not do-while loop: latch predecessor "
"contains exit we optimized out.\n", loop->num);
return false;
}
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Loop %i is do-while loop\n", loop->num);
@ -634,9 +663,9 @@ update_profile_after_ch (class loop *loop,
}
entry_count = e_copy->count ();
}
/* Be sure that we seen all edges we are supposed to update. */
gcc_checking_assert (static_exits->is_empty ()
&& invariant_exits->is_empty ());
/* Be sure that we seen all invariant exit edges we are supposed to update.
We may have recorded some static exists we decided to not duplicate. */
gcc_checking_assert (invariant_exits->is_empty ());
}
namespace {
@ -792,16 +821,43 @@ ch_base::copy_headers (function *fun)
the header to have just a single successor and copying up to
postdominator. */
int nheaders = 0;
int last_win_nheaders = 0;
bool last_win_invariant_exit = false;
ch_decision ret;
hash_set <edge> *invariant_exits = new hash_set <edge>;
hash_set <edge> *static_exits = new hash_set <edge>;
while (should_duplicate_loop_header_p (header, loop, ranger,
&remaining_limit,
invariant_exits,
static_exits))
while ((ret = should_duplicate_loop_header_p (header, loop, ranger,
&remaining_limit,
invariant_exits,
static_exits))
!= ch_impossible)
{
nheaders++;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " Will duplicate bb %i\n", header->index);
if (ret >= ch_win)
{
last_win_nheaders = nheaders;
last_win_invariant_exit = (ret == ch_win_invariant_exit);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " Duplicating bb %i is a win\n",
header->index);
}
/* Duplicate BB if has zero cost but be sure it will not
imply duplication of other BBs. */
else if (ret == ch_possible_zero_cost
&& (last_win_nheaders == nheaders - 1
|| (last_win_nheaders == nheaders - 2
&& last_win_invariant_exit)))
{
last_win_nheaders = nheaders;
last_win_invariant_exit = false;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
" Duplicating bb %i is a win; it has zero cost\n",
header->index);
}
else
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " May duplicate bb %i\n", header->index);
/* Find a successor of header that is inside a loop; i.e. the new
header after the condition is copied. */
@ -811,8 +867,27 @@ ch_base::copy_headers (function *fun)
header = EDGE_SUCC (header, 1)->dest;
}
if (nheaders)
candidates.safe_push ({loop, nheaders, invariant_exits, static_exits});
/* Try to turn loop into do-while. This means ensuring that
last duplicated header will not have loop invariant exit. */
if (last_win_nheaders && last_win_invariant_exit
&& nheaders > last_win_nheaders)
{
last_win_nheaders++;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
" Duplicating additional BB to obtain do-while loop\n");
}
else if (!last_win_nheaders && nheaders && !do_while_loop_p (loop))
{
last_win_nheaders = 1;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
" Duplicating header BB to obtain do-while loop\n");
}
if (last_win_nheaders)
candidates.safe_push ({loop, last_win_nheaders,
invariant_exits, static_exits});
else
{
delete invariant_exits;
@ -844,6 +919,8 @@ ch_base::copy_headers (function *fun)
entry_count += e->count ();
while (n_bbs < candidate.nheaders)
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " Will duplicate bb %i\n", header->index);
/* Find a successor of header that is inside a loop; i.e. the new
header after the condition is copied. */
if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest))
@ -1111,9 +1188,9 @@ pass_ch_vect::execute (function *fun)
/* Apply header copying according to a very simple test of do-while shape. */
bool
pass_ch::process_loop_p (class loop *loop)
pass_ch::process_loop_p (class loop *)
{
return !do_while_loop_p (loop);
return true;
}
/* Apply header-copying to loops where we might enable vectorization. */