[SR-3930] Compact Mangling: Investigate not distinguishing between struct/enum

[ematejska]

Previous ID	SR-3930
Radar	rdar://problem/31411213
Original Reporter	@ematejska
Type	Bug
Status	Resolved
Resolution	Won't Do

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, AffectsABI
Assignee	None
Priority	Medium

md5: 1c4a5caffad9c7e36a34bcbc2f7e6f5f

Issue Description:

Ahead of ABI stability, investigate not distinguishing between struct/enum in mangling structures. This would produce a more compact mangling.

[bob-wilson]

@swift-ci create

[bob-wilson]

We're not planning to do this.

Some comments from Erik Eckstein:

"This would be surprisingly complicated to implement - for a non-obvious reason: We use the old re-mangler to generated backward compatible ObjC runtime names. If we don’t have the enum vs. struct info in the mangling tree we couldn’t do this anymore. Instead we would have to reactivate the old mangler or do something very hacky. This would just be terrible....

This would not produce a more compact mangling, because we still would need one character to represent a nominal type (either sturct or enum). It would just free one character from the mangling operator namespace."