>
> In message <Pine.LNX.4.02A.9903312009540.353-100000@mikeg.weiden.de>you write
> > It's not off-topic, compiler technicalities are very important in the
> > kernel. As to it being optimized away.. it didn't. I think that your
> > initial look was dead center.. the second rdtsc was combined with the
> > first, which is a lot different from throwing it away. (I would find
> > it easy to view combination of two rdtsc insns as a bug tho, given the
> > purpose of that insn :)
> Two asms with idential asm-strings and the same inputs/clobbers can be
> cse'd by the compiler.
>
> Given two asms with the same output, the first may be deleted if the value
> it computes is not used before the second asm (traditional dead code
> elimination).
>
>
> In the example provided, it is cse, not combine that (in my opinion)
> incorrectly eliminated one of the rdtsc asms (the volatile asms between
> the rdtsc asms should have prevented cse from doing that).
>
> You can see this by running the compiler with the "-dap" option, then
> examining the .jump file, then examining the .cse file.
Ah, thanks. I've tried to struggle through these before, but have the
problem that I don't know the order in which they are produced. Can you
(or anyone) spare a hint as to where to find this info? I've looked,
but seemingly in the wrong places. (I just tried strace to find out,
but vfork killed that idea)
-Mike
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