compiler: Constant fold Maps that are safe

For updates of Map literals which may cause an error will be
determined in runtime, i.e. instructions are emitted for those
updates.

The changes in cerl now requires compiler-5.0 to compile because of
is_map/1 guard.

1 files changed, 30 insertions, 2 deletions

diff --git a/lib/compiler/src/cerl.erl b/lib/compiler/src/cerl.erl
index 9024999d7f..61b47ed468 100644
--- a/lib/compiler/src/cerl.erl
+++ b/lib/compiler/src/cerl.erl
@@ -1588,7 +1588,7 @@ ann_c_map(As,Es) ->
     ann_c_map(As, #c_literal{val=#{}}, Es).
 
 ann_c_map(As,#c_literal{val=Mval}=M,Es) when is_map(Mval), map_size(Mval) =:= 0 ->
-    Pairs = [[K,V]||#c_map_pair{key=K,val=V}<-Es],
+    Pairs = [[Ck,Cv]||#c_map_pair{key=Ck,val=Cv}<-Es],
     IsLit = lists:foldl(fun(Pair,Res) ->
 		Res andalso is_lit_list(Pair)
 	end, true, Pairs),
@@ -1599,8 +1599,36 @@ ann_c_map(As,#c_literal{val=Mval}=M,Es) when is_map(Mval), map_size(Mval) =:= 0
 	true ->
 	    #c_literal{anno=As, val=maps:from_list(lists:map(Fun, Pairs))}
 	end;
+ann_c_map(As,#c_literal{val=M},Es) when is_map(M) ->
+    fold_map_pairs(As,Es,M);
 ann_c_map(As,M,Es) ->
-    #c_map{var=M, es = Es, anno = As }.
+    #c_map{var=M, es=Es, anno=As }.
+
+fold_map_pairs(As,[],M) -> #c_literal{anno=As,val=M};
+%% M#{ K => V}
+fold_map_pairs(As,[#c_map_pair{op=#c_literal{val=assoc},key=Ck,val=Cv}=E|Es],M) ->
+    case is_lit_list([Ck,Cv]) of
+	true ->
+	    [K,V] = lit_list_vals([Ck,Cv]),
+	    fold_map_pairs(As,Es,maps:put(K,V,M));
+	false ->
+	    #c_map{var=#c_literal{val=M,anno=As}, es=[E|Es], anno=As }
+    end;
+%% M#{ K := V}
+fold_map_pairs(As,[#c_map_pair{op=#c_literal{val=exact},key=Ck,val=Cv}=E|Es],M) ->
+    case is_lit_list([Ck,Cv]) of
+	true ->
+	    [K,V] = lit_list_vals([Ck,Cv]),
+	    case maps:is_key(K,M) of
+		true -> fold_map_pairs(As,Es,maps:put(K,V,M));
+		false ->
+		    #c_map{var=#c_literal{val=M,anno=As}, es=[E|Es], anno=As }
+	    end;
+	false ->
+	    #c_map{var=#c_literal{val=M,anno=As}, es=[E|Es], anno=As }
+    end;
+fold_map_pairs(As,Es,M) ->
+    #c_map{var=#c_literal{val=M,anno=As}, es=Es, anno=As }.
 
 
 update_c_map(Old,M,Es) ->