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authorBjörn Gustavsson <[email protected]>2010-03-12 09:39:23 +0100
committerBjörn Gustavsson <[email protected]>2010-06-02 11:51:25 +0200
commit7ac0808979534a94617c3391503c961d1ef72755 (patch)
treef929be0d00318569bef8d37ecf316512b17a1b19 /lib/compiler/src
parent1858cb81391d2bce29b4b7620574ca60128cebf7 (diff)
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Evaluate element/2 at compile-time using type information
The erl_expand_records compiler pass translates the following code: h(X) when X#r1.a =:= 1 -> ok. to (essentially): h({r1,V1,V2}=X) when element(2, X) =:= 1 -> ok. Since the guard can only be executed when the pattern matching has succeeded, we know that the second element in the tuple X must have been bound to V2. Thus we can eliminate the call to element/2 like this: h({r1,V1,V2}=X) when V1 =:= 1 -> ok.
Diffstat (limited to 'lib/compiler/src')
-rw-r--r--lib/compiler/src/sys_core_fold.erl29
1 files changed, 16 insertions, 13 deletions
diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index 6202f07479..3e572d4b27 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -1194,19 +1194,22 @@ eval_element(Call, #c_literal{val=Pos}, #c_tuple{es=Es}, _Types) when is_integer
true ->
eval_failure(Call, badarg)
end;
-%% eval_element(Call, #c_literal{val=Pos}, #c_var{name=V}, Types)
-%% when is_integer(Pos) ->
-%% case orddict:find(V, Types#sub.t) of
-%% {ok,#c_tuple{es=Elements}} ->
-%% if
-%% 1 =< Pos, Pos =< length(Elements) ->
-%% lists:nth(Pos, Elements);
-%% true ->
-%% eval_failure(Call, badarg)
-%% end;
-%% error ->
-%% Call
-%% end;
+eval_element(Call, #c_literal{val=Pos}, #c_var{name=V}, Types)
+ when is_integer(Pos) ->
+ case orddict:find(V, Types#sub.t) of
+ {ok,#c_tuple{es=Elements}} ->
+ if
+ 1 =< Pos, Pos =< length(Elements) ->
+ case lists:nth(Pos, Elements) of
+ #c_alias{var=Alias} -> Alias;
+ Res -> Res
+ end;
+ true ->
+ eval_failure(Call, badarg)
+ end;
+ error ->
+ Call
+ end;
eval_element(Call, Pos, Tuple, _Types) ->
case is_not_integer(Pos) orelse is_not_tuple(Tuple) of
true ->