[Bug tree-optimization/80540] New: gcc ICE at -O2 and above on x86_64-linux-gnu in "assign_by_spills"

[helloqirun at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80540

            Bug ID: 80540
           Summary: gcc ICE at -O2 and above on x86_64-linux-gnu in
                    "assign_by_spills"
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: helloqirun at gmail dot com
  Target Milestone: ---

The following code causes an ICE when compiled with the current gcc trunk at
-O2 and above on x86_64-linux-gnu in both 32- and 64-bit modes. Unlike PR79636,
-O0 and -O1 work fine.

Moreover, 

gcc-4.8.5 crashes at all levels;
gcc-4.9 accepts it at all levels;
gcc-5.X,6 accept it at -O1 and -O0, and reject it at -O2 and above.


$ gcc-trunk --version
gcc-trunk (GCC) 8.0.0 20170426 (experimental) [trunk revision 247284]
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.



$ gcc-trunk -O2 abc.c
abc.c: In function ‘fn2’:
abc.c:15:1: error: unable to find a register to spill
 }
 ^
abc.c:15:1: error: this is the insn:
(insn 14 37 36 3 (parallel [
            (set (reg:SI 101 [94])
                (truncate:SI (lshiftrt:DI (mult:DI (sign_extend:DI (reg:SI 102
[100]))
                            (sign_extend:DI (reg:SI 95)))
                        (const_int 32 [0x20]))))
            (clobber (reg:SI 102 [100]))
            (clobber (reg:CC 17 flags))
        ]) "abc.c":5 355 {*smulsi3_highpart_1}
     (expr_list:REG_UNUSED (reg:SI 102 [100])
        (expr_list:REG_DEAD (reg:SI 95)
            (expr_list:REG_UNUSED (reg:CC 17 flags)
                (expr_list:REG_EQUAL (truncate:SI (lshiftrt:DI (mult:DI
(sign_extend:DI (reg:SI 93 [ a ]))
                                (const_int 274877907 [0x10624dd3]))
                            (const_int 32 [0x20])))
                    (nil))))))
abc.c:15:1: internal compiler error: in assign_by_spills, at lra-assigns.c:1476
0xb19c98 _fatal_insn(char const*, rtx_def const*, char const*, int, char
const*)
        ../../gcc/gcc/rtl-error.c:108
0xa07acb assign_by_spills
        ../../gcc/gcc/lra-assigns.c:1476
0xa08526 lra_assign()
        ../../gcc/gcc/lra-assigns.c:1670
0xa03ad4 lra(_IO_FILE*)
        ../../gcc/gcc/lra.c:2451
0x9b9dd1 do_reload
        ../../gcc/gcc/ira.c:5472
0x9b9dd1 execute
        ../../gcc/gcc/ira.c:5656
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.


$ cat abc.c
int g, a;
void fn1() {
  int b = ({
    register __typeof__(0) c asm("rdx");
    g = a / 1000;
    c;
  });
  if (b)
    a = 0;
}
void fn2() {
  switch (g)
  case 0:
  fn1();
}