Hi!
When debugging what turned out to be just a -Wreturn-type reported
failure now being a fatal problem even at -O0, it occurs to me that
because we are not optimizing at -O0, adding the __builtin_unreachable
doesn't bring many optimization advantages (practically just optimize
away epilogue) and so I think I'd prefer to only add those
when optimizing.
Similarly, for UBSan, we instrument these with -fsanitize=return,
part of -fsanitize=unreachable, where we provide nice runtime errors,
but when somebody intentionally turns that off (e.g. to quickly get
past such issues to look for something else), say with
-fsanitize=undefined -fno-sanitize=return, the same error will be
reported as __builtin_unreachable with a cryptic <built-in> location.
I think it is better to just leave it out if -fsanitize=unreachable.
Changed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok
for trunk?
2017-12-05 Jakub Jelinek <ja...@redhat.com>
* cp-gimplify.c (cp_maybe_instrument_return): Don't add
__builtin_unreachable if -O0 or if -fsanitize=unreachable.
* g++.dg/missing-return.C: Add -O to dg-options.
--- gcc/cp/cp-gimplify.c.jj 2017-12-04 22:29:04.759741988 +0100
+++ gcc/cp/cp-gimplify.c 2017-12-04 22:37:07.283784470 +0100
@@ -1554,6 +1554,18 @@ cp_maybe_instrument_return (tree fndecl)
|| !targetm.warn_func_return (fndecl))
return;
+ if (!sanitize_flags_p (SANITIZE_RETURN, fndecl)
+ /* Don't add __builtin_unreachable () if not optimizing, it will not
+ improve any optimizations in that case, just break UB code.
+ Don't add it if -fsanitize=unreachable -fno-sanitize=return either,
+ UBSan covers this with ubsan_instrument_return above where sufficient
+ information is provided, while the __builtin_unreachable () below
+ if return sanitization is disabled will just result in hard to
+ understand runtime error without location. */
+ && (!optimize
+ || sanitize_flags_p (SANITIZE_UNREACHABLE, fndecl)))
+ return;
+
tree t = DECL_SAVED_TREE (fndecl);
while (t)
{
--- gcc/testsuite/g++.dg/missing-return.C.jj 2017-11-06 17:24:11.000000000
+0100
+++ gcc/testsuite/g++.dg/missing-return.C 2017-12-05 00:25:13.028800127
+0100
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-Wreturn-type -fdump-tree-optimized" } */
+/* { dg-options "-Wreturn-type -fdump-tree-optimized -O" } */
int foo(int a)
{
Jakub
