Messages in this thread |  | | | Date | Sun, 18 Sep 2005 22:12:25 +0100 | | From | Al Viro <> | | Subject | Re: p = kmalloc(sizeof(*p), ) |
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On Sun, Sep 18, 2005 at 10:34:16PM +0200, Roman Zippel wrote: > > Ewwwww... I'd say that it qualifies as one hell of a bug (and yes, at least > > 3.3 and 4.0.1 are still doing that). What a mess... > > It's not a bug, it's exactly what you're asking for, e.g. "*p1 = *p2" > translates to memcpy. gcc also can't simply initialize that structure in > place, e.g. you could do something like this (not necessarily useful but > still valid): "*p = (struct foo){..., bar(p),...};". > In the end it all depends on how good gcc can optimize away the memcpy, > but initially there is always a memcpy.
No. Assignment is _not_ defined via memcpy(); it's a primitive that could be implemented that way. Choosing such (pretty much worst-case) implementation in every case is a major bug in code generator.
You _can_ introduce a new local variable for each arithmetic operation in your function and store result of operation in the corresponding variable. As the matter of fact, this is a fairly common intermediate form. However, if compiler ends up leaving all these suckers intact in the final code, it has a serious problem.
Compound literal _is_ an object, all right. However, decision to allocate storage for given object is up to compiler and it's hardly something unusual. "Value of right-hand side is not needed to finish calculating left-hand side, so its storage is fair game from that point on" is absolutely normal. - 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/
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