This has a significant performance impact: processing time is cut in about
half and memory usage is reduced by more than 50%. For example, a
package that previously took 30s and 2.1GiB of memory to link now takes
14s and less than 900MiB of memory.
I had tried to perform this optimization a couple years ago but was
thwarted (I think) by the classifier markers. The previous commit did away
with those. I'm encouraged by the gains from the low-hanging fruit.
* src/current/compiler/linker.xsl
(l:process-empty, l:stack-empty): Convert from l:pstack and
l:sym-stack (respectively) to empty preproc:sym sequences.
(l:depgen-process-sym)[preproc:sym]: Append to sequence rather than
outputting new l:sym-stack tree.
Update all annotations and uses accordingly.
d624ee6d7e