[Bug sanitizer/66880] New: 'error: case label does not reduce to an integer constant' with -fsanitize=shift -std=gnu99.

[chefmax at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66880

            Bug ID: 66880
           Summary: 'error: case label does not reduce to an integer
                    constant' with -fsanitize=shift -std=gnu99.
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chefmax at gcc dot gnu.org
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org,
                    mpolacek at gcc dot gnu.org, ygribov at gcc dot gnu.org
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu

When compile this testcase with -fsanitize=shift -std=gnu99, such an error
happened:

$ cat test.c

int main (int argc, char **argv) {
  switch (argc) {
    case 0xEB << 24: return 1;
    case 1: return 2;
    default: return 0;
  }
}


$ ~/install/master/bin/gcc  -fsanitize=undefined -std=gnu99 test.c
-static-libubsan

1.c: In function ‘main’:
1.c:3:5: error: case label does not reduce to an integer constant
     case 0xEB << 24: return 1;
     ^
max@max:/tmp$ ~/install/master/bin/gcc  -fsanitize=shift -std=gnu99 1.c
-static-libubsan
1.c: In function ‘main’:
1.c:3:5: error: case label does not reduce to an integer constant
     case 0xEB << 24: return 1;
     ^

$ ~/install/master/bin/gcc  -v
Using built-in specs.
COLLECT_GCC=/home/max/install/master/bin/gcc
COLLECT_LTO_WRAPPER=/home/max/install/master/libexec/gcc/x86_64-unknown-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /home/max/workspace/downloads/gcc/configure --enable-multilib
--enable-checking --target=x86_64-unknown-linux-gnu
--host=x86_64-unknown-linux-gnu --build=x86_64-unknown-linux-gnu
--prefix=/home/max/install/master --disable-bootstrap --enable-languages=c,c++
CFLAGS='-g -O0' CXXFLAGS='-g -O0'
Thread model: posix
gcc version 6.0.0 20150710 (experimental) (GCC)

This is caused by this:

Breakpoint 1, check_case_value (loc=7699, value=0x7ffff69712a8) at
/home/max/workspace/downloads/gcc/gcc/c-family/c-common.c:3620
3620          error_at (loc, "case label does not reduce to an integer
constant");
(gdb) call debug_tree(value)
 <compound_expr 0x7ffff69712a8
    type <integer_type 0x7ffff682e7e0 int public SI
        size <integer_cst 0x7ffff682aee8 constant 32>
        unit size <integer_cst 0x7ffff682af00 constant 4>
        align 32 symtab 0 alias set -1 canonical type 0x7ffff682e7e0 precision
32 min <integer_cst 0x7ffff682aea0 -2147483648> max <integer_cst 0x7ffff682aeb8
2147483647>
        pointer_to_this <pointer_type 0x7ffff6848930>>
    side-effects
    arg 0 <call_expr 0x7ffff6833a68
        type <void_type 0x7ffff6848150 void VOID
            align 8 symtab 0 alias set -1 canonical type 0x7ffff6848150
            pointer_to_this <pointer_type 0x7ffff68482a0>>
        side-effects
        fn <addr_expr 0x7ffff696fd20 type <pointer_type 0x7ffff6987a80>
            constant arg 0 <function_decl 0x7ffff69202a0
__builtin___ubsan_handle_shift_out_of_bounds>>
        arg 0 <addr_expr 0x7ffff696fd00 type <pointer_type 0x7ffff69879d8>
            constant arg 0 <var_decl 0x7ffff6836cf0 *.Lubsan_data0>
            1.c:3:15>
        arg 1 <integer_cst 0x7ffff6970a80 constant 235>
        arg 2 <integer_cst 0x7ffff6970a68 constant 24>>
    arg 1 <integer_cst 0x7ffff6970840 type <integer_type 0x7ffff682e7e0 int>
constant -352321536>
    1.c:3:15>
(gdb)