From 5d0874a8f9fd617308d9024783db1e4e24268184 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micha=C5=82=20Muska=C5=82a?= Date: Fri, 27 Apr 2018 12:40:07 +0200 Subject: Introduce is_map_key/2 guard BIF This complements the `map_get/2` guard BIF introduced in #1784. Rationale. `map_get/2` allows accessing map fields in guards, but it might be problematic in more complex guard expressions, for example: foo(X) when map_get(a, X) =:= 1 or is_list(X) -> ... The `is_list/1` part of the guard could never succeed since the `map_get/2` guard would fail the whole guard expression. In this situation, this could be solved by using `;` instead of `or` to separate the guards, but it is not possible in every case. To solve this situation, this PR proposes a `is_map_key/2` guard that allows to check if a map has key inside a guard before trying to access that key. When combined with `is_map/1` this allows to construct a purely boolean guard expression testing a value of a key in a map. Implementation. Given the use case motivating the introduction of this function, the PR contains compiler optimisations that produce optimial code for the following guard expression: foo(X) when is_map(X) and is_map_key(a, X) and map_get(a, X) =:= 1 -> ok; foo(_) -> error. Given all three tests share the failure label, the `is_map_key/2` and `is_map/2` tests are optimised away. As with `map_get/2` the `is_map_key/2` BIF is allowed in match specs. --- lib/compiler/src/beam_dead.erl | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'lib/compiler/src/beam_dead.erl') diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index dbbaae05eb..762c7bdf9e 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -392,6 +392,26 @@ backward([{bif,'or',{f,To0},[Dst,{atom,false}],Dst}=I|Is], D, _ -> backward(Is, D, [I|Acc]) end; +backward([{bif,map_get,{f,FF},[Key,Map],_}=I0, + {test,has_map_fields,{f,FT}=F,[Map|Keys0]}=I1|Is], D, Acc) when FF =/= 0 -> + case shortcut_label(FF, D) of + FT -> + case lists:delete(Key, Keys0) of + [] -> + backward([I0|Is], D, Acc); + Keys -> + Test = {test,has_map_fields,F,[Map|Keys]}, + backward([Test|Is], D, [I0|Acc]) + end; + _ -> + backward([I1|Is], D, [I0|Acc]) + end; +backward([{bif,map_get,{f,FF},[_,Map],_}=I0, + {test,is_map,{f,FT},[Map]}=I1|Is], D, Acc) when FF =/= 0 -> + case shortcut_label(FF, D) of + FT -> backward([I0|Is], D, Acc); + _ -> backward([I1|Is], D, [I0|Acc]) + end; backward([I|Is], D, Acc) -> backward(Is, D, [I|Acc]); backward([], _D, Acc) -> Acc. -- cgit v1.2.3