sys_core_fold: Eliminate crash for map update in guard

sys_core_fold would crash when attempting to optimize this code:

    t() when (#{})#{}->
        c.

2 files changed, 18 insertions, 2 deletions

diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index bb3a9c7628..167383a202 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -214,6 +214,8 @@ opt_guard_try(#c_case{clauses=Cs}=Term) ->
     Term#c_case{clauses=opt_guard_try_list(Cs)};
 opt_guard_try(#c_clause{body=B0}=Term) ->
     Term#c_clause{body=opt_guard_try(B0)};
+opt_guard_try(#c_let{vars=[],arg=#c_values{es=[]},body=B}) ->
+    B;
 opt_guard_try(#c_let{arg=Arg,body=B0}=Term) ->
     case opt_guard_try(B0) of
 	#c_literal{}=B ->
diff --git a/lib/compiler/test/core_fold_SUITE.erl b/lib/compiler/test/core_fold_SUITE.erl
index 4fd1f84569..ab7f36abf7 100644
--- a/lib/compiler/test/core_fold_SUITE.erl
+++ b/lib/compiler/test/core_fold_SUITE.erl
@@ -27,7 +27,8 @@
 	 multiple_aliases/1,redundant_boolean_clauses/1,
 	 mixed_matching_clauses/1,unnecessary_building/1,
 	 no_no_file/1,configuration/1,supplies/1,
-         redundant_stack_frame/1,export_from_case/1]).
+         redundant_stack_frame/1,export_from_case/1,
+         empty_values/1]).
 
 -export([foo/0,foo/1,foo/2,foo/3]).
 
@@ -47,7 +48,8 @@ groups() ->
        multiple_aliases,redundant_boolean_clauses,
        mixed_matching_clauses,unnecessary_building,
        no_no_file,configuration,supplies,
-       redundant_stack_frame,export_from_case]}].
+       redundant_stack_frame,export_from_case,
+       empty_values]}].
 
 
 init_per_suite(Config) ->
@@ -584,5 +586,17 @@ export_from_case_2(Bool, Rec) ->
     end,
     {ok,Result}.
 
+empty_values(_Config) ->
+    case ?MODULE of
+        core_fold_inline_SUITE ->
+            {'EXIT',_} = (catch do_empty_values());
+        _ ->
+            {'EXIT',{function_clause,_}} = (catch do_empty_values())
+    end,
+    ok.
+
+do_empty_values() when (#{})#{} ->
+    c.
+
 
 id(I) -> I.