At some point, pass definitions were heavily macro-ized. Pass
descriptive names were added in two places. This is not only redundant
but a source of confusion. You could waste a lot of time grepping for
the wrong string. I removed all the getName() overrides which, at
around 90 passes, was a fairly significant amount of code bloat.
Any pass that we want to be able to invoke by name from a tool
(sil-opt) or pipeline plan *should* have unique type name, enum value,
commend-line string, and name string. I removed a comment about the
various inliner passes that contradicted that.
Side note: We should be consistent with the policy that a pass is
identified by its type. We have a couple passes, LICM and CSE, which
currently violate that convention.
I am going to run it very early and use it to ensure that extra copies due to my
refactoring of SILGenPattern do not cause COW copies to be introduced.
For now, it does a very simple optimization, namely, it eliminates a copy_value,
with only a destroy_value user on a guaranteed parameter.
It is now disabled behind a flag.
