[LLVMdev] Irreducible CFG from tail duplication

[Florian Brandner]

hi mark,

> It seems that tail duplication can make a reducible CFG irreducible
> (example below).  Is that intentional?  Are there other optimizations
> that have that property?

there has been a discussion on this problem some weeks ago:
http://lists.cs.uiuc.edu/pipermail/llvmdev/2008-June/015247.html

the message includes a patch for taildup, that disables the duplication of 
loop headers. there are some remarks on the patch in follow-up messages, most 
notably it causes some compiltime overhead (~1%-2% on spec benchmarks). note 
that, taildup has been completely removed on trunk.

florian

-- 
Brandner Florian

CD Laboratory - Compilation Techniques for Embedded Processors
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Technische Universität Wien
 
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