Add strict product field demands to lambda binders

This is a follow-up on the first improvement in [D4244#126311].

Consider the following two functions with identical semantics:

module Foo where

{-# LANGUAGE BangPatterns #-}
data Complex a = !a :+ !a

foo :: Complex Double -> Int -> Complex Double
foo !x 0 = x
foo (a :+ b) _ = b :+ a

bar :: Complex Double -> Int -> Complex Double
bar x 0 = x
bar (a :+ b) _ = b :+ a

In the corresponding simplified Core, x gets strictness S(SS) for foo, but only S for bar. We could do better by looking at xs type and see that its a product type with strict fields.

This is because currently only case binders get special treatment for strict product fields through addDataConStrictness.

This ticket tracks if the same is worthwhile for lambda binders, as in bar above. Note that intuitively, this shouldn't make any difference because when we eventually unleash an S demand on a Complex constructor, we add seqDmd on strict fields anyway, amounting to S(SS). So this is only a matter of recording things early because some parts of the analysis code might not be smart enough to add strict field demands by themselves.

Also note that this doesn't touch impliciations on usage analysis at all, where unleashing the same seqDmd twice might mean we accidentally make some product field lose its single-entrieness.

Trac metadata

Trac field	Value
Version	8.5
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions	D4244
BlockedBy
Related
Blocking
CC	simonpj
Operating system
Architecture