beam_utils: Refactor combine_alloc_lists() to cover more lines

There are four uncovered lines in combine_heap_needs/2 and
combine_alloc_lists/2. There is no way to reach starting from
Erlang source code using the standard compiler. However, they
can be reached starting from BEAM assembly code, so we don't
want to remove them.

We could add a test case that covers the lines using assembly
code, but an easier solution is to rewrite the code in a more
generic way using sofs so that the code can be covered with
existing test cases.

1 files changed, 21 insertions, 25 deletions

diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index 1b2a2827cb..941ae95110 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -30,7 +30,7 @@
 
 -export_type([code_index/0,module_code/0,instruction/0]).
 
--import(lists, [map/2,member/2,sort/1,reverse/1,splitwith/2]).
+-import(lists, [flatmap/2,map/2,member/2,sort/1,reverse/1,splitwith/2]).
 
 -define(is_const(Val), (Val =:= nil orelse
                         element(1, Val) =:= integer orelse
@@ -282,16 +282,16 @@ delete_live_annos([]) -> [].
 %% combine_heap_needs(HeapNeed1, HeapNeed2) -> HeapNeed
 %%  Combine the heap need for two allocation instructions.
 
--spec combine_heap_needs(term(), term()) -> term().
+-type heap_need_tag() :: 'floats' | 'words'.
+-type heap_need() :: non_neg_integer() |
+                     {'alloc',[{heap_need_tag(),non_neg_integer()}]}.
+-spec combine_heap_needs(heap_need(), heap_need()) -> heap_need().
 
-combine_heap_needs({alloc,Alloc1}, {alloc,Alloc2}) ->
-    {alloc,combine_alloc_lists(Alloc1, Alloc2)};
-combine_heap_needs({alloc,Alloc}, Words) when is_integer(Words) ->
-    {alloc,combine_alloc_lists(Alloc, [{words,Words}])};
-combine_heap_needs(Words, {alloc,Alloc}) when is_integer(Words) ->
-    {alloc,combine_alloc_lists(Alloc, [{words,Words}])};
 combine_heap_needs(H1, H2) when is_integer(H1), is_integer(H2) ->
-    H1+H2.
+    H1 + H2;
+combine_heap_needs(H1, H2) ->
+    combine_alloc_lists([H1,H2]).
+
 
 %% split_even/1
 %% [1,2,3,4,5,6] -> {[1,3,5],[2,4,6]}
@@ -723,22 +723,18 @@ label(Old, D, Fb) ->
         _ -> Fb(Old)
     end.
 
-%% Help functions for combine_heap_needs.
-
-combine_alloc_lists(Al1, Al2) ->
-    combine_alloc_lists_1(sort(Al1++Al2)).
-
-combine_alloc_lists_1([{words,W1},{words,W2}|T])
-  when is_integer(W1), is_integer(W2) ->
-    [{words,W1+W2}|combine_alloc_lists_1(T)];
-combine_alloc_lists_1([{floats,F1},{floats,F2}|T])
-  when is_integer(F1), is_integer(F2) ->
-    [{floats,F1+F2}|combine_alloc_lists_1(T)];
-combine_alloc_lists_1([{words,_}=W|T]) ->
-    [W|combine_alloc_lists_1(T)];
-combine_alloc_lists_1([{floats,_}=F|T]) ->
-    [F|combine_alloc_lists_1(T)];
-combine_alloc_lists_1([]) -> [].
+%% Help function for combine_heap_needs.
+
+combine_alloc_lists(Al0) ->
+    Al1 = flatmap(fun(Words) when is_integer(Words) ->
+                         [{words,Words}];
+                    ({alloc,List}) ->
+                         List
+                 end, Al0),
+    Al2 = sofs:relation(Al1),
+    Al3 = sofs:relation_to_family(Al2),
+    Al4 = sofs:to_external(Al3),
+    [{Tag,lists:sum(L)} || {Tag,L} <- Al4].
 
 %% live_opt/4.