Messages in this thread | | | Date | Sun, 11 Aug 2002 11:47:22 -0700 | From | Andrew Morton <> | Subject | Re: [patch 4/21] fix ARCH_HAS_PREFETCH |
| |
Alan Cox wrote: > > On Sun, 2002-08-11 at 08:38, Andrew Morton wrote: > > This information loss is unfortunate. Examples: > > > > for (i = 0; i < N; i++) > > prefetch(foo[i]); > > > > Problem is, if `prefetch' is a no-op, the compiler will still > > generate an empty busy-wait loop. Which it must do. > > Why - nothing there is volatile
Because the compiler sees:
for (i = 0; i < N; i++) ;
and it says "ah ha. A busy wait delay loop" and leaves it alone.
It's actually a special-case inside the compiler to not optimise away such constructs. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |