When we have an empty function, things can go wrong with
cfi_startproc/cfi_endproc and a few other things like exceptions. So if
the only thing the function does is a call to __builtin_unreachable,
let's expand that to a __builtin_trap instead. For most targets that
is one instruction wide so it won't hurt things that much and we get
correct behavior for exceptions and some linkers will be better for it.
The only thing I have a concern about is that some targets still
don't define a trap instruction. I tried to emit a nop instead of
an abort but that nop is removed during RTL DCE.
Should we just push targets to define a trap instead?
E.g. BPF, avr and sh are the 3 semi active targets which still don't
have a trap defined.
The QOI idea for basic block reorder is recorded as PR 120004.
Changes since v1:
* v2: Move to final gimple cfg cleanup instead of expand and use
BUILT_IN_UNREACHABLE_TRAP.
Bootstrapped and tested on x86_64-linux-gnu.
PR middle-end/109267
gcc/ChangeLog:
* tree-cfgcleanup.cc (execute_cleanup_cfg_post_optimizing): If the first
non debug statement in the first (and only) basic block is a call
to __builtin_unreachable change it to a call to __builtin_trap.
gcc/testsuite/ChangeLog:
* gcc.dg/pr109267-1.c: New test.
* gcc.dg/pr109267-2.c: New test.
Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
---
gcc/testsuite/gcc.dg/pr109267-1.c | 14 ++++++++++++++
gcc/testsuite/gcc.dg/pr109267-2.c | 14 ++++++++++++++
gcc/tree-cfgcleanup.cc | 14 ++++++++++++++
3 files changed, 42 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr109267-1.c
create mode 100644 gcc/testsuite/gcc.dg/pr109267-2.c
diff --git a/gcc/testsuite/gcc.dg/pr109267-1.c
b/gcc/testsuite/gcc.dg/pr109267-1.c
new file mode 100644
index 00000000000..d6df2c3b49a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr109267-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+/* PR middle-end/109267 */
+
+int f(void)
+{
+ __builtin_unreachable();
+}
+
+/* This unreachable should be changed to be a trap. */
+
+/* { dg-final { scan-tree-dump-times "__builtin_unreachable trap \\\(" 1
"optimized"} } */
+/* { dg-final { scan-tree-dump-not "__builtin_unreachable \\\(" "optimized"} }
*/
diff --git a/gcc/testsuite/gcc.dg/pr109267-2.c
b/gcc/testsuite/gcc.dg/pr109267-2.c
new file mode 100644
index 00000000000..6cd1419a1e3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr109267-2.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+/* PR middle-end/109267 */
+void g(void);
+int f(int *t)
+{
+ g();
+ __builtin_unreachable();
+}
+
+/* The unreachable should stay a unreachable. */
+/* { dg-final { scan-tree-dump-not "__builtin_unreachable trap \\\("
"optimized"} } */
+/* { dg-final { scan-tree-dump-times "__builtin_unreachable \\\(" 1
"optimized"} } */
diff --git a/gcc/tree-cfgcleanup.cc b/gcc/tree-cfgcleanup.cc
index 9a8a668e12b..38a62499f93 100644
--- a/gcc/tree-cfgcleanup.cc
+++ b/gcc/tree-cfgcleanup.cc
@@ -46,6 +46,7 @@ along with GCC; see the file COPYING3. If not see
#include "cgraph.h"
#include "tree-into-ssa.h"
#include "tree-cfgcleanup.h"
+#include "target.h"
/* The set of blocks in that at least one of the following changes happened:
@@ -1530,6 +1531,19 @@ execute_cleanup_cfg_post_optimizing (void)
cleanup_dead_labels ();
if (group_case_labels ())
todo |= TODO_cleanup_cfg;
+
+ basic_block bb = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
+ gimple_stmt_iterator gsi = gsi_start_nondebug_after_labels_bb (bb);
+ /* If the first (and only) bb and the only non debug
+ statement is __builtin_unreachable call, then replace it with a trap
+ so the function is at least one instruction in size. */
+ if (!gsi_end_p (gsi)
+ && gimple_call_builtin_p (gsi_stmt (gsi), BUILT_IN_UNREACHABLE))
+ {
+ gimple_call_set_fndecl (gsi_stmt (gsi), builtin_decl_implicit
(BUILT_IN_UNREACHABLE_TRAP));
+ update_stmt (gsi_stmt (gsi));
+ }
+
if ((flag_compare_debug_opt || flag_compare_debug)
&& flag_dump_final_insns)
{
--
2.43.0
