mozilla/rust — pull request #9722 by alexcrichton (2013-10-04 23:06:26+00:00)
Title: Cache more results of const_eval

According to http://huonw.github.io/isrustfastyet/mem/#012f909, the "const
marking" pass generates about 400MB of extra memory during compilation. It
appears that this is due to two different factors:

1. There is a `ccache` map in the ty::ctxt which is only ever used in this
pass, so this commit moves the map out of the ty::ctxt struct and into
just this pass's visitor. This turned out to not benefit that much in
memory (as indicated by http://i.imgur.com/Eo4iOzK.png), but it's helpful
to do nonetheless.

2. During const_eval, there are a lot of lookups into decoding inlined items
from external crates. There is no caching involved here, so the same
static or variant could be re-translated many times. After adding
separate caches for variants and statics, the memory peak of compiling
rustc decreased by 200MB (as evident by http://i.imgur.com/ULAUMtq.png)

The culmination of this is basically a slight reorganization of a caching map
for the const_eval pass along with a 200MB decrease in peak memory usage when
compiling librustc.