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In the v3_life pass, it is assumed that a 'match_fail' primop
only occur at the top-level and at the end of a function.
But this code:
do_split_cases(A) ->
case A of
x ->
Z = dummy1;
_ ->
Z = dummy2,
a=b
end,
Z.
will be optimized by sys_core_fold to the following code:
'split_cases'/1 =
fun (_cor0) ->
let <_cor7,Z> =
case _cor0 of
<'x'> when 'true' ->
< 'dummy1','dummy1' >
<_cor6> when 'true' ->
%% Here follows a 'match_fail' primop inside
%% multiple return values:
< primop 'match_fail'({'badmatch','b'}),'dummy2' >
end
in
Z
moving the 'match_fail' primop into a "values" construction.
In the future, we would like to get rid of the v3_life pass (it is
there for historical reasons), so in the mean-time we prefer to not
add more code to it by generalizing the handling of 'match_fail'.
Since the 'match_fail' primop can be simulated by erlang:error/{1,2},
the simplest solution is to translate 'match_fail' to a call to
erlang:error/{1,2} in v3_kernel and remove the handling of
'match_fail' in v3_life and v3_codegen.
It is tempting to get rid of 'match_fail' also in the Core Erlang
format, but there are two issues:
- Removing the support for 'match_fail' completely may break tools
that generate Core Erlang code. We should not do that in a minor
release.
- There is no easy way to generate a 'function_clause' exception
that will remain correct if it will be inlined into another
function. (Calling "erlang:error(function_clause, Args)" is
fine only if it is not inlined into another function.) A good
solution probably involves introducing new instructions, which
is better done in a major release.
Noticed-by: Håkan Matsson
Minimized-test-case-by: Erik Søe Sørensen
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