[Bug middle-end/102566] [i386] GCC should emit LOCK BTS for simple bit-test-and-set operations with std::atomic

["thiago at kde dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102566

--- Comment #11 from Thiago Macieira <thiago at kde dot org> ---
$ for ((i=0;i<32;++i)); do ~/dev/gcc/bin/gcc "-DCONSTANT=(1<<$i)" -S -o - -O2
/tmp/test.cpp | grep bts; done 
        lock btsl       $0, (%rdi)
        lock btsl       $1, (%rdi)
        lock btsl       $2, (%rdi)
        lock btsl       $3, (%rdi)
        lock btsl       $4, (%rdi)
        lock btsl       $5, (%rdi)
        lock btsl       $6, (%rdi)
        lock btsl       $7, (%rdi)
        lock btsl       $8, (%rdi)
        lock btsl       $9, (%rdi)
        lock btsl       $10, (%rdi)
        lock btsl       $11, (%rdi)
        lock btsl       $12, (%rdi)
        lock btsl       $13, (%rdi)
        lock btsl       $14, (%rdi)
        lock btsl       $15, (%rdi)
        lock btsl       $16, (%rdi)
        lock btsl       $17, (%rdi)
        lock btsl       $18, (%rdi)
        lock btsl       $19, (%rdi)
        lock btsl       $20, (%rdi)
        lock btsl       $21, (%rdi)
        lock btsl       $22, (%rdi)
        lock btsl       $23, (%rdi)
        lock btsl       $24, (%rdi)
        lock btsl       $25, (%rdi)
        lock btsl       $26, (%rdi)
        lock btsl       $27, (%rdi)
        lock btsl       $28, (%rdi)
        lock btsl       $29, (%rdi)
        lock btsl       $30, (%rdi)
        lock btsl       $31, (%rdi)

And after changing to long:

$ for ((i=32;i<64;++i)); do ~/dev/gcc/bin/gcc "-DCONSTANT=(1L<<$i)" -S -o - -O2
/tmp/test.cpp | grep bts; done
        lock btsq       $32, (%rdi)
        lock btsq       $33, (%rdi)
        lock btsq       $34, (%rdi)
        lock btsq       $35, (%rdi)
        lock btsq       $36, (%rdi)
        lock btsq       $37, (%rdi)
        lock btsq       $38, (%rdi)
        lock btsq       $39, (%rdi)
        lock btsq       $40, (%rdi)
        lock btsq       $41, (%rdi)
        lock btsq       $42, (%rdi)
        lock btsq       $43, (%rdi)
        lock btsq       $44, (%rdi)
        lock btsq       $45, (%rdi)
        lock btsq       $46, (%rdi)
        lock btsq       $47, (%rdi)
        lock btsq       $48, (%rdi)
        lock btsq       $49, (%rdi)
        lock btsq       $50, (%rdi)
        lock btsq       $51, (%rdi)
        lock btsq       $52, (%rdi)
        lock btsq       $53, (%rdi)
        lock btsq       $54, (%rdi)
        lock btsq       $55, (%rdi)
        lock btsq       $56, (%rdi)
        lock btsq       $57, (%rdi)
        lock btsq       $58, (%rdi)
        lock btsq       $59, (%rdi)
        lock btsq       $60, (%rdi)
        lock btsq       $61, (%rdi)
        lock btsq       $62, (%rdi)
        lock btsq       $63, (%rdi)

But:

$ cat /tmp/test2.cpp 
#include <atomic>
bool tbit(std::atomic<long> &i)
{
  return i.fetch_or(1, std::memory_order_relaxed) & (~1);
}
$ ~/dev/gcc/bin/gcc -S -o - -O2 /tmp/test2.cpp
        .file   "test.cpp"
        .text
/tmp/test.cpp: In function ‘bool tbit(std::atomic<long int>&)’:
/tmp/test.cpp:2:6: error: type mismatch in binary expression
    2 | bool tbit(std::atomic<long> &i)
      |      ^~~~
long int

long unsigned int

__int_type

_9 = _6 & -2;
during GIMPLE pass: fab
/tmp/test.cpp:2:6: internal compiler error: verify_gimple failed
0x119fbba verify_gimple_in_cfg(function*, bool)
        /home/tjmaciei/src/gcc/gcc/tree-cfg.c:5576
0x106ced7 execute_function_todo
        /home/tjmaciei/src/gcc/gcc/passes.c:2042
0x106d8fb execute_todo
        /home/tjmaciei/src/gcc/gcc/passes.c:2096
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