On 08/31/14 06:18, Segher Boessenkool wrote:
On Fri, Aug 29, 2014 at 11:58:37PM -0600, Jeff Law wrote:
One could argue that this mess is a result of trying to optimize a reg
that is set more than once. Though I guess that might be a bit of a
big hammer.
It works fine in other cases, and is quite beneficial for e.g. optimising
instruction sequences that set a fixed carry register twice.
How common is that?
While we don't have any formal SSA-like properties in RTL, we're
certainly better off if we can avoid unnecessary cases where a single
pseudo is set more than once and these days I wouldn't expect too many
cases where have multiple sets appearing in a dep chain that can be
processed by combine (and if we do one could easily argue those dep
chains should be simplified).
Jeff
