Erlc internal consistency error (suspected to be about CSE of division)

[RobinMorisset]

On the following code:

-module(cse_div).
-compile([export_all]).

f1(_, _) ->
    0.

f2(V) ->
    f1(
        is_tuple(V) orelse (1 / V),
        (1 / V) andalso true
    ).

erlc crashes with the following error message:

cse_div:1: function f2/1+15:
Internal consistency check failed - please report this bug.
Instruction: {bif,fdiv,{f,0},[{fr,0},{fr,1}],{fr,0}}
Error: {uninitialized_reg,{fr,0}}:

The bug still reproduces if I replace both instances of 1 / V by 0 / V, but not if I only replace one, so I suspect that the problem is related to Common Subexpression Elimination of the division.

The call to is_tuple(V) can be replaced by is_list(V) and the bug still reproduces, but the crash disappears if it is removed altogether.

[bjorng]

Thanks for the bug report.

CSE is a reasonable hypothesis, but that is not the problem. The problem is in the pass that rewrites general arithmetic instructions to specialised floating point instructions.

The linked pull request resolves the problem. It will be included in OTP 25.1 and also in the next patch for OTP 24.

[RobinMorisset]

Thank you for this quick answer and investigation!