On Tue, Sep 27, 2011 at 4:56 PM, Jeff Law <l...@redhat.com> wrote:
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> On 09/27/11 01:30, Richard Guenther wrote:
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>>
>>> It knows something about prephitmp.6_1 and thus could simplify
>>> D.2734_9 = prephitmp_6.1 & D.2732_7; to D.2734_9 = D.2732_7; But
>>> admittedly I have no idea if DOM tries to simplify things other
>>> than comparisons within the jump threading machinery ... (the
>>> above block basically ends in if (D.2729_6 != 0 &&
>>> prephitmp_6.1), so I'd guess it's worth to simplify the (complex)
>>> conditional expression).
> Jump threading will enter simplified expressions into the hash tables
> for every statement in the block in an effort to utilize any
> information available to determine the result of the comparison.
> However, those simplifications aren't ever reflected back into the IL.
>
> The thing to remember is jump threading is tasked detecting cases
> where the control statement has a predetermined destination utilizing
> path sensitive information. Expanding it to do general path
> sensitive optimizations is possible, but at even greater cost.
Yeah, I realize that. It's just this case is the non-cfg form of
if (pretmp)
if (D.1234)
...
where jump-threading would probably handle the CFG variant just fine.
Oh well ;)
Richard.
