Piers Cawley <[EMAIL PROTECTED]> wrote: > Leopold Toetsch <[EMAIL PROTECTED]> writes:
[ calculating registers to save ] >> ... once per sub per location where the sub is called from. But there >> isn't any knowledge that a sub might be called. So the cost is actually >> more per PMC instruction that might eventually run a PASM MMD. This is, >> when its done right, or ... > No. Once per compilation unit. An example: .sub foo # a lot of string handling code # and some PMCs $P0 = concat $P0, $S0 # <<< 1) calculate: save P, S here # now a lot of float code # no strings used any more # and no branch back to 1) $N1 = 47.11 # $N1's live starts here $P0 = $P1 + $N1 # <<< 2) calculate: save P, N regs $P2 = $P0 + $N1 # <<< 3) calculate: save P regs # no N reg used here .end At 1) the caller is not interested in preserving N-registers, these aren't used there. Saving everything, the caller needs saving, ends up with C<saveall> in non trivial subroutines. Using your proposal would need a lot of storage for the saved register ranges. If the calculation is done based on the called subroutine, it's not unlikely that only a few registers have to be preserved, e.g. no N-registers for the overloaded C<concat> and no string registers for the overloaded C<add>. This doesn't violate the principle of caller saves: all that needs preserving from the caller's POV is preserved. leo
