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

[Richard Biener]

On Thu, 26 Nov 2015, Alan Lawrence wrote:

> 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

See also PR68549 for why I think this happens "by design".  Thus
I think we need to revert the checking when 
LOOPS_MAY_HAVE_MULTIPLE_LATCHES for now.

Richard.