Hi! Normally empty blocks without successors (result of __builtin_unreachable () somewhere in RTL) aren't considered as forwarder_block_p, because they don't satisfy single_succ_p. But e.g. during cross-jumping fake edges to exit are added and then they suddenly satisfy this predicate, which confuses the cross-jumping among other things (normally cross-jumping attempts to be careful with no real successor blocks if there isn't a noreturn call with REG_ARGS_SIZE note, but if it believes those are forwarders, it doesn't check hard).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/6.2? 2016-07-19 Jakub Jelinek <ja...@redhat.com> PR rtl-optimization/71916 * cfgrtl.c (contains_no_active_insn_p): Return false also for bb which have a single succ fake edge. * gcc.c-torture/compile/pr71916.c: New test. --- gcc/cfgrtl.c.jj 2016-05-11 15:15:49.000000000 +0200 +++ gcc/cfgrtl.c 2016-07-19 16:38:20.362303955 +0200 @@ -574,8 +574,10 @@ contains_no_active_insn_p (const_basic_b { rtx_insn *insn; - if (bb == EXIT_BLOCK_PTR_FOR_FN (cfun) || bb == ENTRY_BLOCK_PTR_FOR_FN (cfun) - || !single_succ_p (bb)) + if (bb == EXIT_BLOCK_PTR_FOR_FN (cfun) + || bb == ENTRY_BLOCK_PTR_FOR_FN (cfun) + || !single_succ_p (bb) + || (single_succ_edge (bb)->flags & EDGE_FAKE) != 0) return false; for (insn = BB_HEAD (bb); insn != BB_END (bb); insn = NEXT_INSN (insn)) --- gcc/testsuite/gcc.c-torture/compile/pr71916.c.jj 2016-07-19 16:43:37.610371787 +0200 +++ gcc/testsuite/gcc.c-torture/compile/pr71916.c 2016-07-19 16:43:20.000000000 +0200 @@ -0,0 +1,36 @@ +/* PR rtl-optimization/71916 */ + +int a, b, c, d, f, g; +short h; + +short +foo (short p1) +{ + return a >= 2 || p1 > 7 >> a ? p1 : p1 << a; +} + +void +bar (void) +{ + for (;;) + { + int i, j[3]; + h = b >= 2 ? d : d >> b; + if (foo (f > h ^ c)) + { + d = 0; + while (f <= 2) + { + char k[2]; + for (;;) + k[i++] = 7; + } + } + else + for (;;) + g = j[2]; + if (g) + for (;;) + ; + } +} Jakub