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Ignore conditions guarding __builtin_unreachable in inliner metrics

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This extends my last year attempt to make inliner metric ignore
conditionals guarding __builtin_unreachable.  Compared to previous
patch, this one implements a "mini-dce" in ipa-fnsummary to avoid
accounting all statements that are only used to determine conditionals
guarding __builtin_unnecesary.  These will be removed later once value
ranges are determined.

While working on this, I noticed that we do have a lot of dead code while
computing fnsummary for early inline. Those are only used to apply
large-function growth, but it seems there is enough dead code to make this
valud kind of irrelevant.  Also there seems to be quite a lot of const/pure
calls that can be cheaply removed before we inline them.  So I wonder if we
want to run one DCE before early inlining.

gcc/ChangeLog:

	PR tree-optimization/109442
	* ipa-fnsummary.cc (builtin_unreachable_bb_p): New function.
	(guards_builtin_unreachable): New function.
	(STMT_NECESSARY): New macro.
	(mark_stmt_necessary): New function.
	(mark_operand_necessary): New function.
	(find_necessary_statements): New function.
	(analyze_function_body): Use it.

gcc/testsuite/ChangeLog:

	* gcc.dg/ipa/fnsummary-1.c: New test.
This commit is contained in:
Jan Hubicka 2024-11-16 14:04:32 +01:00
parent 064c6493c8
commit cee7d080d5
2 changed files with 189 additions and 1 deletions
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181
gcc/ipa-fnsummary.cc
View file

@ -2674,6 +2674,169 @@ points_to_possible_sra_candidate_p (tree t)
return false;
}
/* Return true if BB only calls builtin_unreachable.
We skip empty basic blocks, debug statements, clobbers and predicts.
CACHE is used to memoize already analyzed blocks. */
static bool
builtin_unreachable_bb_p (basic_block bb, vec<unsigned char> &cache)
{
if (cache[bb->index])
return cache[bb->index] - 1;
gimple_stmt_iterator si;
auto_vec <basic_block, 4> visited_bbs;
bool ret = false;
while (true)
{
bool empty_bb = true;
visited_bbs.safe_push (bb);
cache[bb->index] = 3;
for (si = gsi_start_nondebug_bb (bb);
!gsi_end_p (si) && empty_bb;
gsi_next_nondebug (&si))
{
if (gimple_code (gsi_stmt (si)) != GIMPLE_PREDICT
&& !gimple_clobber_p (gsi_stmt (si))
&& !gimple_nop_p (gsi_stmt (si)))
{
empty_bb = false;
break;
}
}
if (!empty_bb)
break;
else
bb = single_succ_edge (bb)->dest;
if (cache[bb->index])
{
ret = cache[bb->index] == 3 ? false : cache[bb->index] - 1;
goto done;
}
}
if (gimple_call_builtin_p (gsi_stmt (si), BUILT_IN_UNREACHABLE)
|| gimple_call_builtin_p (gsi_stmt (si), BUILT_IN_UNREACHABLE_TRAP))
ret = true;
done:
for (basic_block vbb:visited_bbs)
cache[vbb->index] = (unsigned char)ret + 1;
return ret;
}
static bool
guards_builtin_unreachable (basic_block bb, vec<unsigned char> &cache)
{
edge_iterator ei;
edge e;
FOR_EACH_EDGE (e, ei, bb->succs)
if (builtin_unreachable_bb_p (e->dest, cache))
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
"BB %i ends with conditional guarding __builtin_unreachable;"
" conditinal is unnecesary\n", bb->index);
return true;
}
return false;
}
#define STMT_NECESSARY GF_PLF_1
/* If STMT is not already marked necessary, mark it, and add it to the
worklist if ADD_TO_WORKLIST is true. */
static inline void
mark_stmt_necessary (gimple *stmt, auto_vec<gimple *> &worklist)
{
gcc_assert (stmt);
if (gimple_plf (stmt, STMT_NECESSARY))
return;
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Marking useful stmt: ");
print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
fprintf (dump_file, "\n");
}
gimple_set_plf (stmt, STMT_NECESSARY, true);
worklist.safe_push (stmt);
}
/* Mark the statement defining operand OP as necessary. */
static inline void
mark_operand_necessary (tree op, auto_vec<gimple *> &worklist)
{
gimple *stmt = SSA_NAME_DEF_STMT (op);
if (gimple_nop_p (stmt))
return;
mark_stmt_necessary (stmt, worklist);
}
/* Mark all statements that will remain in the body after optimizing out
conditionals guarding __builtin_unreachable which we keep to preserve
value ranges. */
static void
find_necessary_statements (struct cgraph_node *node)
{
struct function *my_function = DECL_STRUCT_FUNCTION (node->decl);
auto_vec<unsigned char, 10> cache;
basic_block bb;
auto_vec<gimple *> worklist;
cache.safe_grow_cleared (last_basic_block_for_fn (cfun));
/* Mark all obviously necessary statements. */
FOR_EACH_BB_FN (bb, my_function)
{
for (gimple_stmt_iterator gsi = gsi_start_phis (bb);
!gsi_end_p (gsi); gsi_next (&gsi))
gimple_set_plf (gsi_stmt (gsi), STMT_NECESSARY, false);
for (gimple_stmt_iterator bsi = gsi_start_bb (bb); !gsi_end_p (bsi);
gsi_next_nondebug (&bsi))
{
gimple *stmt = gsi_stmt (bsi);
gimple_set_plf (stmt, STMT_NECESSARY, false);
if (gimple_has_side_effects (stmt)
|| (is_ctrl_stmt (stmt)
&& (gimple_code (stmt) != GIMPLE_COND
|| !guards_builtin_unreachable (bb, cache)))
|| gimple_store_p (stmt))
mark_stmt_necessary (stmt, worklist);
}
}
while (worklist.length () > 0)
{
gimple *stmt = worklist.pop ();
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "processing: ");
print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
fprintf (dump_file, "\n");
}
if (gimple_code (stmt) == GIMPLE_PHI)
for (unsigned int k = 0; k < gimple_phi_num_args (stmt); k++)
{
tree arg = PHI_ARG_DEF (stmt, k);
if (TREE_CODE (arg) == SSA_NAME)
mark_operand_necessary (arg, worklist);
}
else
{
ssa_op_iter iter;
tree use;
FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
mark_operand_necessary (use, worklist);
}
}
}
/* Analyze function body for NODE.
EARLY indicates run from early optimization pipeline. */
@ -2718,7 +2881,7 @@ analyze_function_body (struct cgraph_node *node, bool early)
calculate_dominance_info (CDI_DOMINATORS);
calculate_dominance_info (CDI_POST_DOMINATORS);
if (!early)
loop_optimizer_init (LOOPS_NORMAL | LOOPS_HAVE_RECORDED_EXITS);
loop_optimizer_init (LOOPS_NORMAL | LOOPS_HAVE_RECORDED_EXITS);
else
{
ipa_check_create_node_params ();
@ -2765,6 +2928,7 @@ analyze_function_body (struct cgraph_node *node, bool early)
if (fbi.info)
compute_bb_predicates (&fbi, node, info, params_summary);
find_necessary_statements (node);
const profile_count entry_count = ENTRY_BLOCK_PTR_FOR_FN (cfun)->count;
order = XNEWVEC (int, n_basic_blocks_for_fn (cfun));
nblocks = pre_and_rev_post_order_compute (NULL, order, false);
@ -2830,6 +2994,21 @@ analyze_function_body (struct cgraph_node *node, bool early)
!gsi_end_p (bsi); gsi_next_nondebug (&bsi))
{
gimple *stmt = gsi_stmt (bsi);
if (!gimple_plf (stmt, STMT_NECESSARY))
{
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, " skipping unnecesary stmt ");
print_gimple_stmt (dump_file, stmt, 0);
}
/* TODO: const calls used only to produce values for
builtion_unreachable guards should not be accounted. However
we still want to inline them and this does does not work well
with the cost model. For now account them as usual. */
if (!is_gimple_call (stmt)
|| gimple_call_internal_p (stmt))
continue;
}
int this_size = estimate_num_insns (stmt, &eni_size_weights);
int this_time = estimate_num_insns (stmt, &eni_time_weights);
int prob;

9
gcc/testsuite/gcc.dg/ipa/fnsummary-1.c Normal file
View file

@ -0,0 +1,9 @@
/* { dg-options "-O2 -fdump-ipa-fnsummary-details" } */
int
test(int a, int b)
{
if (a / b > 10)
__builtin_unreachable ();
}
/* { dg-final { scan-ipa-dump "ends with conditional guarding __builtin_unreachable" "fnsummary" } } */
/* { dg-final { scan-ipa-dump-times "skipping unnecesary stmt" 2 "fnsummary" } } */