== Remove sizeof op ==

=== Description ===

The PIR op {{{sizeof}}} was removed.

=== Rationale ===

This op was used to determine the size of a PMC's C-level struct given a numerical PMC type id.  This op was deprecated because numerical PMC id values should not be exposed to PIR-level code.

=== Replacement ===
  
No replacement currently exists because no core, library or HLL code was found to rely on this op.  If this functionality is needed, a string-based version could easily be implemented.  See TT #633 for further discussion.

== Replace STRING_is_null with Parrot_str_is_null ==

=== Description ===

The C-level macro STRING_is_null was replaced with Parrot_str_is_null.

=== Rationale ===

Make string null checks look like a Parrot API function.

=== Replacement ===

Replace uses of the C function STRING_is_null with Parrot_str_is_null.  Parrot_str_is_null is a drop-in replacement for STRING_is_null.  See TT #1585 for (very sparse) further discussion.

== Remove in-place substr op variants ==

=== Description ===

All variants of the PIR op {{{substr}}} which mutate an argument in-place were removed.

=== Rationale ===

Parrot moved to immutable strings for performance reasons.  With immutable strings, a PIR-level string is never changed once it's been created.  This means that ops that work on a string in-place no longer make sense.

=== Replacement ===

PIR code should be changed as follows:
{{{
    #old version
    substr $S0, $I0, $I1, $S1

    #new version
    $S0 = replace $S0, $I0, $I1, $S1  
}}}

See also r46055 for more examples.  See TT #1450 for further discussion.