> Am 16.11.2024 um 14:08 schrieb Jan Hubicka <hubi...@ucw.cz>:
>
> Ignore conditions guarding __builtin_unreachable in inliner metrics
>
> This patch 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.
I would not have expected a ‚lot‘ of dead const function calls. By same
argument we should rather run CCP before inlining as that tends to prune most
dead code early?
Richard
> Bootstrapped/regtested x86_64-linux, comitted.
>
> 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 --git a/gcc/ipa-fnsummary.cc b/gcc/ipa-fnsummary.cc
> index e921cd495f6..87e08dad846 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 00000000000..abc9dcfee38
> --- /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"
> } } */
