[Bug target/55139] __atomic store does not support __ATOMIC_HLE_RELEASE

["andi-gcc at firstfloor dot org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55139

--- Comment #1 from Andi Kleen <andi-gcc at firstfloor dot org> 2012-11-07 04:03:53 UTC ---
This is an interesting one. This is the gcc code:

enum memmodel
{
  MEMMODEL_RELAXED = 0,
  MEMMODEL_CONSUME = 1,
  MEMMODEL_ACQUIRE = 2,
  MEMMODEL_RELEASE = 3,
  MEMMODEL_ACQ_REL = 4,
  MEMMODEL_SEQ_CST = 5,
  MEMMODEL_LAST = 6
};
#define MEMMODEL_MASK ((1<<16)-1)

 enum memmodel model;

  model = get_memmodel (CALL_EXPR_ARG (exp, 2));
  if ((model & MEMMODEL_MASK) != MEMMODEL_RELAXED
      && (model & MEMMODEL_MASK) != MEMMODEL_SEQ_CST
      && (model & MEMMODEL_MASK) != MEMMODEL_RELEASE)
    {
      error ("invalid memory model for %<__atomic_store%>");
      return NULL_RTX;
    }

HLE_STORE is 1 << 16, so outside the enum range

But when looking at the assembler we see that the & MEMMODEL_MASK
gets optimized away, it just generates a direct sequence of 32bit cmps.  

This makes all the != fail, even though they should succeed

I presume the optimizer assumes nothing can be outside the enum.

I tried to expand the enum by adding

  MEMMODEL_ARCH1 =  1 << 16,
  MEMMODEL_ARCH2 =  1 << 17,
  MEMMODEL_ARCH3 =  1 << 18,
  MEMMODEL_ARCH4 =  1 << 19

But still doesn't work.

Questions:
- Is it legal for the optimizer to assume this?
- Why does extending the enum not help?

We could fix it by not using an enum here of course, but I wonder if this is an
underlying optimizer bug.