[Bug rtl-optimization/59724] [4.9 Regression] ICE : in rtl_verify_bb_layout, at cfgrtl.c

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59724

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 31778
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31778&action=edit
gcc49-pr59724.patch

Ugh, what a mess.  So, while ifcvt wants flow_find_head_matching_sequence to
count only active insns, so that it matches it's counting, when
try_head_merge_bb calls it, counting only active insns is problematic, because
the count is used to find a minimum number of insns that match.  Now, in the
testcase we first try a pair of bbs where there is a match of 2 active insns
and 1 non-active, then a pair where there is a match of only 2 active insns and
no non-active.  As 2 == 2, we take the first pair as shortest sequence, but we
remember for that the last matching insn (which is the non-active one).

The attached patch reverts the try_head_merge_bb and makes
flow_find_head_matching_sequence behave differently between when called from
try_head_merge_bb and ifcvt.