On Thu, Aug 16, 2007 at 01:24:42AM +0530, Satyam Sharma wrote:

[ The Cc: list scares me. Should probably trim it. ]

Trim away!  ;-)

On Wed, 15 Aug 2007, Paul E. McKenney wrote:

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On Wed, Aug 15, 2007 at 08:31:25PM +0200, Segher Boessenkool wrote:

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How does the compiler know that msleep() has got barrier()s?

Because msleep_interruptible() is in a separate compilation unit,
the compiler has to assume that it might modify any arbitrary global.

No; compilation units have nothing to do with it, GCC can optimise
across compilation unit boundaries just fine, if you tell it to
compile more than one compilation unit at once.

Last I checked, the Linux kernel build system did compile each .c file
as a separate compilation unit.

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What you probably mean is that the compiler has to assume any code
it cannot currently see can do anything (insofar as allowed by the
relevant standards etc.)

I think this was just terminology confusion here again. Isn't "any code
that it cannot currently see" the same as "another compilation unit",
and wouldn't the "compilation unit" itself expand if we ask gcc to
compile more than one unit at once? Or is there some more specific
"definition" for "compilation unit" (in gcc lingo, possibly?)

This is indeed my understanding -- "compilation unit" is whatever the
compiler looks at in one go.  I have heard the word "module" used for
the minimal compilation unit covering a single .c file and everything
that it #includes, but there might be a better name for this.

							Thanx, Paul