[source]

compiler/coreSyn/CoreTidy.hs

Note [Tidy IdInfo]

[note link]

All nested Ids now have the same IdInfo, namely vanillaIdInfo, which should save some space; except that we preserve occurrence info for two reasons:

(a) To make printing tidy core nicer

(b) Because we tidy RULES and InlineRules, which may then propagate
    via --make into the compilation of the next module, and we want
    the benefit of that occurrence analysis when we use the rule or
    or inline the function.  In particular, it's vital not to lose
    loop-breaker info, else we get an infinite inlining loop

Note that tidyLetBndr puts more IdInfo back.

Note [Preserve evaluatedness]

[note link]

Consider

data T = MkT !Bool ….(case v of MkT y ->

let z# = case y of

True -> 1# False -> 2#

in …)

The z# binding is ok because the RHS is ok-for-speculation, but Lint will complain unless it can see that. So we preserve the evaluated-ness on ‘y’ in tidyBndr.

(Another alternative would be to tidy unboxed lets into cases, but that seems more indirect and surprising.)

Note [Preserve OneShotInfo]

[note link]

We keep the OneShotInfo because we want it to propagate into the interface. Not all OneShotInfo is determined by a compiler analysis; some is added by a call of GHC.Exts.oneShot, which is then discarded before the end of the optimisation pipeline, leaving only the OneShotInfo on the lambda. Hence we must preserve this info in inlinings. See Note [The oneShot function] in MkId.

This applies to lambda binders only, hence it is stored in IfaceLamBndr.