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RE: floor on i386
- To: Brad Lucier <lucier at math dot purdue dot edu>
- Subject: RE: floor on i386
- From: Chris Lattner <sabre at nondot dot org>
- Date: Wed, 12 Sep 2001 14:04:17 -0500 (CDT)
- Cc: <gcc at gcc dot gnu dot org>
> If one had tree nodes or RTL nodes to express the sequence
> Save rounding mode
> Change rounding mode to round-down
> Convert to integer
> Restore rounding mode
> then perhaps the rounding mode change changes could be moved
> outside of loops where they occur, if there were no floating-point
> instructions in the loop that needed the currently set rounding mode.
Actually you could probably represent this by adding a "hard register"
that effectively is the rounding mode flags. Doing this seems like a
natural way to allow existing optimizations to get rid of the
redundancies that are killing GCC here... and you wouldn't have to add any
new RTL semantics...
-Chris
http://www.nondot.org/~sabre/os/
http://www.nondot.org/MagicStats/