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Re: [tree-ssa] Loop header copying on trees


In message <20040216135454.GA23822@atrey.karlin.mff.cuni.cz>, Zdenek Dvorak wri
tes:
 >Hello,
 >
 >>  > The jump threading on tree-ssa does this kind of loop header copying
 >>  >already, so I assume it might no longer be true (although I haven't
 >>  >tested it).
 >> Yes, we get a certain amount of virtual header copying via jump threading.
 >> 
 >> It would certainly be interesting to see if loop header copying at the
 >> tree level generally makes things larger or smaller so that we could
 >> make an informed decision :-)
 >
 >on gcc from specint benchmark:
 >
 >-O2 -ftree-ch: 1447502
 >-O2 -fno-tree-ch: 1429678
 >
 >-Os -ftree-ch: 1175935
 >-Os -fno-tree-ch: 1160095
Ok.  That argues pretty convincingly that -Os should imply no header copying,
at least when we're using your tree version.  It's not a huge win, but
it's a win.


jeff



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