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Subject: [Bug target/55966] __atomic_fetch_* generate wrong code for HLE
Date: Mon, 14 Jan 2013 19:06:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55966

--- Comment #1 from Andi Kleen <andi-gcc at firstfloor dot org> 2013-01-14 19:06:02 UTC ---
Here's a test case. This requires the libstdc++ HLE patch from
http://gcc.gnu.org/ml/gcc-patches/2013-01/msg00673.html

g++ -std=gnu++0x

#include <atomic>

#define ACQ memory_order_acquire | __memory_order_hle_acquire
#define REL memory_order_release | __memory_order_hle_release

int main()
{
  using namespace std;
  atomic_ulong au = ATOMIC_VAR_INIT(0);

  if (!au.fetch_and(1, ACQ))
    au.fetch_and(-1, REL);

  unsigned lock = 0;
  __atomic_fetch_and(&lock, 1, __ATOMIC_HLE_ACQUIRE|__ATOMIC_ACQUIRE);

  return 0;
}

The first fetch_and generates incorrectly:

.L2:
        movq    %rax, %rcx
        movq    %rax, %rdx
        andl    $1, %ecx
        lock; cmpxchgq  %rcx, -24(%rsp)
        jne     .L2


The second generates correctly:

        lock; 
        .byte   0xf3
        andq    $-1, -24(%rsp)


The __atomic_fetch_and generates correctly:

     lock; 
        .byte   0xf2
        andl    $1, -28(%rsp)


The first fetch_and should generate the same code sequence.