Eliminate internal consistency failure #6189
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When attempting to compile the following code:
foo(V) when (V / V < (V orelse true)); V; V ->
(V = (a =/= V)) orelse 0.
the `beam_validator` pass produces the following message:
t:1: function foo/1+12:
Internal consistency check failed - please report this bug.
Instruction: {test,is_eq_exact,{f,9},[{x,1},{atom,true}]}
Error: {type_conflict,{t_atom,[true]},{t_atom,[a]}}:
The type conflict mentioned refers to the expression `a =/= V`. At
the point of its evaluation, `V` is known to `beam_validator` to be
the atom `true`; thus, evaluation of `a =/= V` is redundant because the
result is always `false`.
The root cause of the problem is that `beam_validator` has a stronger
type analysis for `=/=` expressions than `beam_ssa_type`. By
strengthening the type analysis for `=/=` in `beam_ssa_type`, the
offending redundant tests are removed and `beam_validator` is again
silent.
It turns out that stronger type analysis causes a new problem for
code such as:
foobar(L) when L =/= [], is_list(L), L =/= [], hd(L) ->
ok.
See the added comment and code in beam_types for a description of
the problem and its solution.
Fixes erlang#6183
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When attempting to compile the following code:
the
beam_validatorpass produces the following message:The type conflict mentioned refers to the expression
a =/= V. Atthe point of its evaluation,
Vis known tobeam_validatorto bethe atom
true; thus, evaluation ofa =/= Vis redundant because theresult is always
false.The root cause of the problem is that
beam_validatorhas a strongertype analysis for
=/=expressions thanbeam_ssa_type. Bystrengthening the type analysis for
=/=inbeam_ssa_type, theoffending redundant tests are removed and
beam_validatoris againsilent.
Fixes #6183