Comment author: @hhugo

Note that it works fine with 4.04.0+beta2

Comment author: @hhugo

most probably related to #7374

Comment author: @damiendoligez

Indeed. Bisecting points to this commit: 8811d34

Comment author: @garrigue

Fixed by commit 02d7c27.

Needed to call wrap_trace_gadt_instances.

Comment author: @hhugo

Js_of_ocaml now compiles, but there is a huge performance regression

$ ocamlfind ocamlc -w +A-4-7-9-37-38-41-44-45 -pp "camlp4o syntax/pa_js.cmo" -safe-string -package lwt,uchar -c -g xmlHttpRequest.ml -dtimings
all: 55.327s
preprocessing(xmlHttpRequest.ml): 0.001s
typing(xmlHttpRequest.ml): 55.239s
transl(xmlHttpRequest.ml): 0.080s
generate(xmlHttpRequest.ml): 0.005s

Comment author: @hhugo

There is a big performance regression

Comment author: @hhugo

step to reproduce:
opam install js_of_ocaml --deps-only --yes
git clone https://github.com/ocsigen/js_of_ocaml.git
cd js_of_ocaml
make -C lib xmlHttpRequest.cmo

with 4.04.0+beta2, I get :

$ ocamlfind ocamlc -w +A-4-7-9-37-38-41-44-45 -pp "camlp4o syntax/pa_js.cmo" -safe-string -package lwt,uchar -c -g xmlHttpRequest.ml -dtimings
all: 0.247s
preprocessing(xmlHttpRequest.ml): 0.001s
typing(xmlHttpRequest.ml): 0.174s
transl(xmlHttpRequest.ml): 0.064s
generate(xmlHttpRequest.ml): 0.005s

Comment author: @garrigue

I did expect a performance regression, but not that big indeed.
If you can leave me 24 hours, I'll try to find a solution.
I.e., we shouldn't need to expand absolutely all types to check that there is no occurence.

Comment author: @garrigue

Commit c20a709 seems to solve the performance problem.
It only starts expanding everything when exploring a constrained type parameter.
But it's still going to be potentially very expensive in that case.

@hhugo Could you check that it solves the problem for your whole code base?

Comment author: @hhugo

Problem solved. Thanks