[Bug target/68520] New: ICE on valid code at -O3 on x86_64-linux-gnu in quick_push, at vec.h:845

["su at cs dot ucdavis.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68520

            Bug ID: 68520
           Summary: ICE on valid code at -O3 on x86_64-linux-gnu in
                    quick_push, at vec.h:845
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The following code causes an ICE when compiled with the current gcc trunk at
-O3 on x86_64-linux-gnu in both 32-bit and 64-bit modes.

It is a regression from 5.2.x.


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20151122 (experimental) [trunk revision 230719] (GCC) 
$ 
$ gcc-trunk -O2 -c small.c
$ gcc-5.2 -O3 -c small.c
$ 
$ gcc-trunk -O3 -c small.c
small.c: In function âfn2â:
small.c:10:1: internal compiler error: in quick_push, at vec.h:845
 }
 ^

0xac60d2 vec<basic_block_def*, va_heap, vl_embed>::quick_push(basic_block_def*
const&)
        ../../gcc-trunk/gcc/vec.h:845
0xac60d2 vec<basic_block_def*, va_heap, vl_ptr>::quick_push(basic_block_def*
const&)
        ../../gcc-trunk/gcc/vec.h:1503
0xac60d2 try_shrink_wrapping(edge_def**, bitmap_head*, rtx_insn*)
        ../../gcc-trunk/gcc/shrink-wrap.c:714
0x870058 thread_prologue_and_epilogue_insns()
        ../../gcc-trunk/gcc/function.c:6021
0x870a92 rest_of_handle_thread_prologue_and_epilogue
        ../../gcc-trunk/gcc/function.c:6543
0x870a92 execute
        ../../gcc-trunk/gcc/function.c:6585
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.
$ 


------------------------------


int a, b, c, d; 

void
fn2 ()
{
  if (c)
    for (; d; d = a+b)
      for (c = 0; c < 2; c++) 
        fn2 ();
}