[dataflow] less useless work/memory on bb's without artificial defs/uses

Paolo Bonzini paolo.bonzini@lu.unisi.ch
Fri Mar 30 13:19:00 GMT 2007

If there is no artificial def or use in the basic block,
DF already avoids creating bitmaps for no use.  However,
it does keep "in" and "top" bitmaps separate, which is
useless and consumes memory.

This patch allows "in" and "top" pointers to share the
same bitmap.

Bootstrapped/regtested i686-pc-linux-gnu, I don't know
exactly how much it saves but I guess some 0.5%.


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