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c288ab87 added beam_reorder to move get_tuple_element instructions.
Compiling code such as the following would crash the compiler:
alloc(_U1, _U2, R) ->
V = R#alloc.version,
Res = id(V),
_ = id(0),
Res.
The crash would occur because the following two instructions:
{get_tuple_element,{x,2},1,{x,1}}.
{allocate_zero,1,2}.
were swapped and rewritten to:
{allocate_zero,1,1}.
{get_tuple_element,{x,2},1,{x,1}}.
That transformation is not safe because the allocate_zero instruction
would kill {x,2}, which is the register that is holding the reference
to the tuple. Only do the transformation when the tuple reference is
in an x register with a lower number than the destination register.
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