Hi,
this was suggested earlier somewhere, but I can not find the thread.
C++ has assume attribute that expands int
if (conditional)
__builtin_unreachable ()
We do not want to account the conditional in inline heuristics since
we know that it is going to be optimized out.
Bootstrapped/regtested x86_64-linux, will commit it later today if
thre are no complains.
gcc/ChangeLog:
* ipa-fnsummary.cc (builtin_unreachable_bb_p): New function.
(analyze_function_body): Do not account conditionals guarding
builtin_unreachable calls.
gcc/testsuite/ChangeLog:
* gcc.dg/ipa/fnsummary-1.c: New test.
diff --git a/gcc/ipa-fnsummary.cc b/gcc/ipa-fnsummary.cc
index a5f5a50c8a5..987da29ec34 100644
--- a/gcc/ipa-fnsummary.cc
+++ b/gcc/ipa-fnsummary.cc
@@ -2649,6 +2649,54 @@ points_to_possible_sra_candidate_p (tree t)
return false;
}
+/* Return true if BB is 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;
+}
+
/* Analyze function body for NODE.
EARLY indicates run from early optimization pipeline. */
@@ -2743,6 +2791,8 @@ analyze_function_body (struct cgraph_node *node, bool
early)
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);
+ auto_vec<unsigned char, 10> cache;
+ cache.safe_grow_cleared (last_basic_block_for_fn (cfun));
for (n = 0; n < nblocks; n++)
{
bb = BASIC_BLOCK_FOR_FN (cfun, order[n]);
@@ -2901,6 +2951,24 @@ analyze_function_body (struct cgraph_node *node, bool
early)
}
}
+ /* Conditionals guarding __builtin_unreachable will be
+ optimized out. */
+ if (gimple_code (stmt) == GIMPLE_COND)
+ {
+ edge_iterator ei;
+ edge e;
+ FOR_EACH_EDGE (e, ei, bb->succs)
+ if (builtin_unreachable_bb_p (e->dest, cache))
+ {
+ if (dump_file)
+ fprintf (dump_file,
+ "\t\tConditional guarding __builtin_unreachable;
ignored\n");
+ this_time = 0;
+ this_size = 0;
+ break;
+ }
+ }
+
/* TODO: When conditional jump or switch is known to be constant, but
we did not translate it into the predicates, we really can account
just maximum of the possible paths. */
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..a0ece0c300b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/fnsummary-1.c
@@ -0,0 +1,8 @@
+/* { dg-options "-O2 -fdump-ipa-fnsummary" } */
+int
+test(int a)
+{
+ if (a > 10)
+ __builtin_unreachable ();
+}
+/* { dg-final { scan-ipa-dump "Conditional guarding __builtin_unreachable"
"fnsummary" } } */
