http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60418
--- Comment #26 from H.J. Lu <hjl.tools at gmail dot com> --- This patch avoids removing preheader when optimizing since preheader will be added back later even if it is removed: diff --git a/gcc/tree-cfgcleanup.c b/gcc/tree-cfgcleanup.c index 926d300..af5b24b 100644 --- a/gcc/tree-cfgcleanup.c +++ b/gcc/tree-cfgcleanup.c @@ -328,7 +328,10 @@ tree_forwarder_block_p (basic_block bb, bool phi_wanted) (LOOPS_MAY_HAVE_MULTIPLE_LATCHES)); } else if (bb->loop_father == loop_outer (dest->loop_father)) - return !loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS); + /* Preserve preheader when optimizing since it will be added + back later. */ + return !(optimize + || loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS)); /* Always preserve other edges into loop headers that are not simple latches or preheaders. */ return false;