Strictness is not preserved under -O1

With -O0, the attached code prints:

> /usr/local/ghc/ghc-8.4.1.0/bin/ghc -O0 src/foo.hs; and ./src/foo
[1 of 1] Compiling Main             ( src/foo.hs, src/foo.o ) [Optimisation flags changed]
Linking src/foo ...
("exec",0)
("depth",0)
("exec",1)
("depth",0)

But with -O1, it prints:

> /usr/local/ghc/ghc-8.4.1.0/bin/ghc -O1 src/foo.hs; and ./src/foo
[1 of 1] Compiling Main             ( src/foo.hs, src/foo.o )
Linking src/foo ...
("depth",0)
("depth",0)

Reproduced with 8.4.1 and 8.6.2. Doesn't seem to happen under 8.2.0

Trac metadata

Trac field	Value
Version	8.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	me@alang.ca
Operating system
Architecture