compiler: Fix incorrect aliasing in matching tuples #9833
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frej
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May 13, 2025
| transformable1(L, start) -> | ||
| %ssa% (_, Arg1) when post_ssa_opt -> |
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%% You should use %ssa% xfail (_, Arg1) when post_ssa_opt -> and not just comment them out in bulk, that way you'll notice all the relevant test cases when the optimization is re-enabled .
Fix erlang#9813. This is a safe but pessimistic fix. Disabled test cases and optimizations will be enabled again in a future commit.
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frej
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Previously all bifs selected by the erl_internal:comp_op/2 predicate was erroneously considered safe from an aliasing perspective. This is not true as they, depending on the argument types, could access internal elements of a term which has been destructively updated. As this makes the destructive update visible, this is illegal and should not happen. To fix this problem, we have to consider all comparison bifs as aliasing operations, thus avoiding the problem described above. Unfortunately this is a very pessimistic solution, and by making use of type information we can avoid forced aliasing when it can be determined that the comparison bif will be reduced to a simple tag test. This is less conservative fix than the one presented in erlang#9833. Co-authored-by: Isabell H. <isabell@erlang.org> Closes erlang#9813.
frej
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Previously all bifs selected by the erl_internal:comp_op/2 predicate was erroneously considered safe from an aliasing perspective. This is not true as they, depending on the argument types, could access internal elements of a term which has been destructively updated. As this makes the destructive update visible, this is illegal and should not happen. To fix this problem, we have to consider all comparison bifs as aliasing operations, thus avoiding the problem described above. Unfortunately this is a very pessimistic solution, and by making use of type information we can avoid forced aliasing when it can be determined that the comparison bif will be reduced to a simple tag test. This is less conservative fix than the one presented in erlang#9833. Co-authored-by: Isabell H. <isabell@erlang.org> Closes erlang#9813.
lucioleKi
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May 14, 2025
compiler: Fix alias analysis bug (less conservative version of #9833)
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Fix #9813. This is a safe but pessimistic fix. Disabled test cases and optimizations will be enabled again in a future commit.