Fix unsafe code generation for binary matching #9341
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The internal instructions `bs_checked_get` and `bs_checked_skip` have confusing names. One might think that they do some extra checking, while the opposite is true. Rename them to `bs_ensured_get` and `bs_ensured_skip` to make the connection to the `bs_ensure` instruction clearer.
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The compiler could sometimes generate unsafe code when
matching literal data in a binary. For example:
t(Data) ->
<<Rest/bits>> = Data,
{_, Bits} = ext:ernal(Rest),
case Rest of
<<0, _:Bits>> -> not_empty;
<<>> -> empty
end.
The generated code for the first clause of the `case` would
look like this:
{bs_match,{f,20},{y,2},{commands,[{'=:=',nil,8,0}]}}.
That is unsafe because the first command in a `bs_match` instruction
must always be an `ensure*` instruction to ensure that the bitstring
is of sufficient size.
This unsafe code generation was introduced in 60f8f9e.
This commit ensures that a `bs_match_string` instruction will be
emitted instead of a `bs_match` instruction:
{test,bs_match_string,{f,20},[{y,2},8,{string,<<0>>}]}.
Fixes erlang#9304
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lucioleKi
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Jan 28, 2025
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