https://gcc.gnu.org/g:cee7d080d5c2a5fb8125878998b742c040ec88b4
commit r15-5336-gcee7d080d5c2a5fb8125878998b742c040ec88b4
Author: Jan Hubicka <hubi...@ucw.cz>
Date: Sat Nov 16 14:04:32 2024 +0100
Ignore conditions guarding __builtin_unreachable in inliner metrics
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.
Diff:
---
gcc/ipa-fnsummary.cc | 181 ++++++++++++++++++++++++++++++++-
gcc/testsuite/gcc.dg/ipa/fnsummary-1.c | 9 ++
2 files changed, 189 insertions(+), 1 deletion(-)
diff --git a/gcc/ipa-fnsummary.cc b/gcc/ipa-fnsummary.cc
index e921cd495f69..87e08dad8467 100644
--- a/gcc/ipa-fnsummary.cc
+++ b/gcc/ipa-fnsummary.cc
@@ -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;
diff --git a/gcc/testsuite/gcc.dg/ipa/fnsummary-1.c
b/gcc/testsuite/gcc.dg/ipa/fnsummary-1.c
new file mode 100644
index 000000000000..abc9dcfee38d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/fnsummary-1.c
@@ -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"
} } */
