[PATCH] Improve verification of loop->latch in verify_loop_structure

[Alan Lawrence]

This caused an ICE compiling value.c from gdb on
aarch64-none-linux-gnu; the testcase, after preprocessing on aarch64,
ICEs on both aarch64 and x86_64, but is about 1MB - I'm working on
reducing that down to something small enough to post...

$ ./gcc/xgcc -B ./gcc -O2 -g value.c
../../binutils-gdb/gdb/value.c: In function ‘show_convenience’:
../../binutils-gdb/gdb/value.c:2615:1: error: loop 3’s latch is missing
../../binutils-gdb/gdb/value.c:2615:1: internal compiler error: in
verify_loop_structure, at cfgloop.c:1669
0x71e653 verify_loop_structure()
        /work/alalaw01/src2/gcc/gcc/cfgloop.c:1669
0x97c6ae checking_verify_loop_structure
        /work/alalaw01/src2/gcc/gcc/cfgloop.h:325
0x97c6ae loop_optimizer_init(unsigned int)
        /work/alalaw01/src2/gcc/gcc/loop-init.c:106
0x97c78a rtl_loop_init
        /work/alalaw01/src2/gcc/gcc/loop-init.c:398
0x97c78a execute
        /work/alalaw01/src2/gcc/gcc/loop-init.c:425

--Alan