[Simh] clang (was Re: XCode and LTO)

[Mark Pizzolato - Info Comm]

On Friday, April 27, 2012, at 10:44 AM, Sergey Oboguev wrote:
> Declaring "loopval" as volatile (and perhaps global, rather than on-stack, to
> reduce chances of compiler disregarding volatile declaration) might do the
> trick.

The goal really isn't to cause a memory reference, but really to avoid the inlining on this specific function.  We're trying to do enough 'spinning' to slow things down predictably here.

My inclination is to:
               
               #if defined(_MSC_VER)
               #define NOINLINE __declspec(noinline)
               #elif defined(__GNUC__)
               #define NOINLINE __attribute__((noinline))
               #else
               #define NOINLINE
               #endif

               int32 NOINLINE rom_swapb(int32 val)

- Mark

> ----- Original Message ----
> From: Craig A. Berry <craigberry at mac.com>
> Subject: [Simh] clang (was Re:  XCode and LTO)
> 
> 
> The comments in the code say, "To avoid smart compilers, the loopval
> variable is referenced in the function arguments so that the function
> expression is not loop invariant," which led me to the lucky guess that the
> compiler was inlining the function and then optimizing away the inlined code.
> So I made the following
> (non-portable) change:
> 
> [...]
> 
> If anyone knows of a more portable way to prevent inlining of rom_swapb(),
> it seems like it would be a  good idea to do so.