Remove global state from gcc/tracer.c

[Richard Henderson]

On 05/23/2013 12:06 PM, Richard Henderson wrote:
> Another thing I should mention while you're doing all of these static function
> to class member conversions is that as written we're losing target-specific
> optimizations that can be done on purely local functions.  This is trivially
> fixed by placing these new classes in an anonymous namespace.

At which point it occurs to me that we don't need to distinguish between static
and normal member methods, nor play with sub-state structures.  All we need to
require is that IPA constant propagation sees that the initial "this" argument
is passed a constant value, and let it propagate and eliminate.

E.g.

namespace {

class pass_state
{
  private:
    int x, y, z;

  public:
    constexpr pass_state()
      : x(0), y(0), z(0)
    { }

    void doit();

  private:
    void a();
    void b();
    void c();
};

// ...

} // anon namespace

#ifdef GLOBAL_STATE
static pass_state ps;
#endif

void toplev()
{
#ifndef GLOBAL_STATE
  pass_state ps;
#endif
  ps.doit();
}

With an example that's probably too small, I verified that gcc will eliminate
all of the this parameters with GLOBAL_STATE defined.  It's certainly something
worth investigating further, as this scheme has the least amount of boilerplate
of any so far advanced.


r~