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split pp_predec() from pp_preinc() and improve
pp_preinc() handles both ++$x and --$x (and the integer variants
pp_i_preinc/dec). Split it into two separate functions, as handling
both inc and dec in the same function requires 3 extra conditionals.
At the same time make the code more efficient.
As currently written it:
1) checked for "bad" SVs (such as read-only) and croaked;
2) checked for a IOK-only SV and directly incremented the IVX slot;
3) else called out to sv_inc() to handle the more complex cases.
This commit combines the checks in (1) and (2) into one single big
check of flags, and anything "bad" simply skips the IOK-only code
and calls sv_dec(), which can do its own checking of read-only etc
and croak if necessary. Porting/bench.pl shows the following raw numbers
for ++$x ($x lexical and holding an integer):
before after
-------- --------
Ir 77.0 56.0
Dr 30.0 24.0
Dw 10.0 10.0
COND 12.0 9.0
IND 2.0 2.0
COND_m -0.1 0.0
IND_m 2.0 2.0
Even having split the function into two, the combined size of the two new
functions is smaller than the single previous function.