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_peep.erl | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'lib/compiler/src/beam_peep.erl') diff --git a/lib/compiler/src/beam_peep.erl b/lib/compiler/src/beam_peep.erl index eb3192fe8f..920fb00397 100644 --- a/lib/compiler/src/beam_peep.erl +++ b/lib/compiler/src/beam_peep.erl @@ -77,6 +77,12 @@ peep([{bif,tuple_size,_,[_]=Ops,Dst}=I|Is], SeenTests0, Acc) -> %% Kill all remembered tests that depend on the destination register. SeenTests = kill_seen(Dst, SeenTests1), peep(Is, SeenTests, [I|Acc]); +peep([{bif,map_get,_,[Key,Map],Dst}=I|Is], SeenTests0, Acc) -> + %% Pretend that we have seen {test,has_map_fields,_,[Map,Key]} + SeenTests1 = gb_sets:add({has_map_fields,[Map,Key]}, SeenTests0), + %% Kill all remembered tests that depend on the destination register. + SeenTests = kill_seen(Dst, SeenTests1), + peep(Is, SeenTests, [I|Acc]); peep([{bif,_,_,_,Dst}=I|Is], SeenTests0, Acc) -> %% Kill all remembered tests that depend on the destination register. SeenTests = kill_seen(Dst, SeenTests0), -- cgit v1.2.3