Original bug ID: 5580
Reporter: jfc
Assigned to: @xavierleroy
Status: closed (set by @xavierleroy on 2015-12-11T18:19:30Z)
Resolution: fixed
Priority: normal
Severity: minor
Platform: x86-64
OS: Linux
Version: 3.12.1
Target version: 4.01.0+dev
Fixed in version: 4.01.0+dev
Category: back end (clambda to assembly)
Monitored by: @hcarty

Bug description

Consider this program:

type t = False | True
let of_bool = function true -> True | false -> False
let x = of_bool true

x should be assigned the constant True but ocamlopt generates a runtime comparison (true != false) to decide the result of of_bool.

Closure.simplif_prim_pure receives the arguments

p = Pintcomp Cneq
approxs = [Value_constptr 1; Value_integer 0]

If both approximations were Value_integer the comparison would be simplified.
The function does not know how to compare a constptr and an integer.

If I change simplif_prim_pure to add a case matching [Value_constptr x; Value_integer y] similarly to [Value_integer x; Value_integer y] code generation improves. I don't understand the compiler well enough to know if that is the correct solution.