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authorBjörn Gustavsson <[email protected]>2018-09-01 10:57:33 +0200
committerBjörn Gustavsson <[email protected]>2018-09-03 10:47:24 +0200
commit47a2ff39ac75c69b41f90f05a63fd9a2e6c0b36a (patch)
treef6ac446058b62541b7ec14dfc28a21a06c5cbc7e /.dir-locals.el
parent31e7b5ab0b72acbbca649b99ade82bba145cc390 (diff)
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Introduce a put_tuple2 instruction
Sometimes when building a tuple, there is no way to avoid an extra `move` instruction. Consider this code: make_tuple(A) -> {ok,A}. The corresponding BEAM code looks like this: {test_heap,3,1}. {put_tuple,2,{x,1}}. {put,{atom,ok}}. {put,{x,0}}. {move,{x,1},{x,0}}. return. To avoid overwriting the source register `{x,0}`, a `move` instruction is necessary. The problem doesn't exist when building a list: %% build_list(A) -> [A]. {test_heap,2,1}. {put_list,{x,0},nil,{x,0}}. return. Introduce a new `put_tuple2` instruction that builds a tuple in a single instruction, so that the `move` instruction can be eliminated: %% make_tuple(A) -> {ok,A}. {test_heap,3,1}. {put_tuple2,{x,0},{list,[{atom,ok},{x,0}]}}. return. Note that the BEAM loader already combines `put_tuple` and `put` instructions into an internal instruction similar to `put_tuple2`. Therefore the introduction of the new instruction will not speed up execution of tuple building itself, but it will be less work for the loader to load the new instruction.
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