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Interprocedural and multi-file object files...

Posted on 2005-03-04
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Last Modified: 2010-04-01
Help of my compiler:
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Enable and specify the scope of Interprocedural (IP) Optimizations:
/Qip     enable single-file IP optimizations (within files, same as /Ob2)
/Qipo[n] enable multi-file IP optimizations (between files)
/Qipo_c  generate a multi-file object file (ipo_out.obj)
/Qipo_S  generate a multi-file assembly file (ipo_out.asm)
...

What is:
interprocedural (IP) Optimizations ?
and what are the advantages of multi-file object files?
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Question by:IAmATeddyBear
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grg99 earned 500 total points
ID: 13458852
usually whenever a compiler sees a function call, it has to stop optimizing, as it has no way of knowing what the called function is going to do with registers.

But a really smart compiler could keep track of each function it has compiled and its register usage, in order to do a better job of optimization.

Usually a compiler resets all its tables after compiling each source file.  But what if one source file calls functions in another, separately compiled source file?   The compiler normally wouldnt know anything about those externally compiled functions, so it wouldnt be able to optimize against them.

But a REALLY clever compiler could keep that information, perhaps in a comment record in the object file.  Then it just might be able to read up that comment record in order to get knowledge about that previously compiled function.

this is rather hard to do correctly--  the poor compiler has to check a whole lot of things to ensure the external function was compile din a optimization-compatible way.  

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by:IAmATeddyBear
ID: 13466854
OK.
Thanks a lot.
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