Aurelien Jarno
a17f24e08d
The copy propagation pass tries to keep track what is a copy of what and what has copy of what, and in addition it keep a circular list of of all the copies. Unfortunately this doesn't fully work: a mov from a temp which has a state "COPY" changed it into a state "HAS_COPY". Later when this temp is used again, it is considered has not having copy and thus no propagation is done. This patch fixes that by removing the hiearchy between copies, and thus only keeping a "COPY" state both meaning "is a copy" and "has a copy". The decision of which copy to use is deferred to the actual temp replacement. At this stage there is not one best choice to do, but only better choices than others. For doing the best choice the operation would have to be parsed in reversed to know if a temp is going to be used later or not. That what is done by the liveness analysis. At this stage it is known that globals will be always live, that local temps will be dead at the end of the translation block, and that the temps will be dead at the end of the basic block. This means that this stage should try to replace temps by local temps or globals and local temps by globals. Reviewed-by: Richard Henderson <rth@twiddle.net> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Read the documentation in qemu-doc.html or on http://wiki.qemu.org - QEMU team