[Bug c/78583] New: ICE on valid C code at -O3 on x86_64-linux-gnu (internal compiler error: in simplify_truncation)

[chengniansun at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78583

            Bug ID: 78583
           Summary: ICE on valid C code at -O3 on x86_64-linux-gnu
                    (internal compiler error: in simplify_truncation)
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com
  Target Milestone: ---

$ 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/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 7.0.0 20161129 (experimental) [trunk revision 242953] (GCC) 
$ 
$ 
$ gcc-trunk -O3 small.c
small.c: In function ‘main’:
small.c:10:1: internal compiler error: in simplify_truncation, at
simplify-rtx.c:640
 }
 ^
0xbc17bc simplify_truncation
        ../../gcc-source-trunk/gcc/simplify-rtx.c:640
0xbc069e simplify_unary_operation_1
        ../../gcc-source-trunk/gcc/simplify-rtx.c:1193
0xbc069e simplify_unary_operation(rtx_code, machine_mode, rtx_def*,
machine_mode)
        ../../gcc-source-trunk/gcc/simplify-rtx.c:877
0xbc1070 simplify_gen_unary(rtx_code, machine_mode, rtx_def*, machine_mode)
        ../../gcc-source-trunk/gcc/simplify-rtx.c:384
0xbc12a5 simplify_truncation
        ../../gcc-source-trunk/gcc/simplify-rtx.c:773
0xbc21e8 simplify_gen_subreg(machine_mode, rtx_def*, machine_mode, unsigned
int)
        ../../gcc-source-trunk/gcc/simplify-rtx.c:6259
0x12a4f2e gen_lowpart_for_combine
        ../../gcc-source-trunk/gcc/combine.c:11465
0x12a65d3 get_last_value
        ../../gcc-source-trunk/gcc/combine.c:13373
0x12a6671 if_then_else_cond
        ../../gcc-source-trunk/gcc/combine.c:9165
0x12a6749 if_then_else_cond
        ../../gcc-source-trunk/gcc/combine.c:9035
0x12a6732 if_then_else_cond
        ../../gcc-source-trunk/gcc/combine.c:9034
0x12b3d0d combine_simplify_rtx
        ../../gcc-source-trunk/gcc/combine.c:5604
0x12b6572 subst
        ../../gcc-source-trunk/gcc/combine.c:5487
0x12b6228 subst
        ../../gcc-source-trunk/gcc/combine.c:5432
0x12b604a subst
        ../../gcc-source-trunk/gcc/combine.c:5355
0x12b784a try_combine
        ../../gcc-source-trunk/gcc/combine.c:3272
0x12bd181 combine_instructions
        ../../gcc-source-trunk/gcc/combine.c:1265
0x12bd181 rest_of_handle_combine
        ../../gcc-source-trunk/gcc/combine.c:14581
0x12bd181 execute
        ../../gcc-source-trunk/gcc/combine.c:14626
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.
$ 
$ cat small.c
int a[1];
int b;
unsigned short c;
void fn1(int p1) { b = a[a[a[a[a[a[a[a[b ^ p1]]]]]]]]; }

int main() {
  long d = c;
  fn1(d & d >> 8 & 5);
  return 0;
}
$