[Bug tree-optimization/68017] New: ICE on valid code at -O3 with -g enabled on x86_64-linux-gnu: cannot update SSA form

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68017

            Bug ID: 68017
           Summary: ICE on valid code at -O3 with -g enabled on
                    x86_64-linux-gnu: cannot update SSA form
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          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 with -g enabled 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 20151019 (experimental) [trunk revision 228969] (GCC) 
$ 
$ gcc-trunk -O3 -c small.c
$ gcc-trunk -O2 -g -c small.c 
$ gcc-5.2 -O3 -g -c small.c
$ 
$ gcc-trunk -O3 -g -c small.c
small.c: In function ‘fn2’:
small.c:10:1: error: statement uses released SSA name:
 fn2 ()
 ^
# DEBUG D#4 => _5 + _24
The use of _24 should have been replaced
small.c:10:1: error: statement uses released SSA name:
# DEBUG D#5 => _5 + _25
The use of _25 should have been replaced
small.c:10:1: internal compiler error: cannot update SSA form
0xb5fc1c update_ssa(unsigned int)
        ../../gcc-trunk/gcc/tree-into-ssa.c:3206
0xa0ccbf execute_function_todo
        ../../gcc-trunk/gcc/passes.c:1943
0xa0d5a3 execute_todo
        ../../gcc-trunk/gcc/passes.c:2033
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.
$ 


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


long long a;

short
fn1 (short p1, unsigned short p2)
{
  return p1 + p2;
}

short
fn2 ()
{
  int b = a ? fn1 (fn2 (), a) : 0;
  return b;
}