RFH: intra-procedure optimizations "CALL_REALLY_USED_REGISTERS"

[BjÃrn Haase <bjoern dot m dot haase at web dot de>]

Hello,

The avr port presently misses possible intra-procedure optimizations 
concerning register use. Optimizations are missed when 1) calling a leaf 
function that is 2) defined in the same unit as a the caller and 3) clobbers 
only a subset of the call-clobbered registers. Presently I observe that the 
caller still saves all of the "CALL_REALLY_USED_REGISTERS" whether they are 
*really* used or not.

Is there a way to make leaf functions to be compiled first so that when 
starting with non-leaf functions in the same unit expand could insert 
detailed information on which subset of registers is actually clobbered by 
calls to leaf functions?

When reading the comments in cgraph.c for the cgraph_optimize function 
"Backend can then use this information to modify calling conventions" it 
seems to me that there is an interface already for modifying the calling 
convention. Is there a port that uses it so that one could find out what the 
interface looks like?

Yours,

Bjoern Haase