Merge pull request #7271 from frej/frej/fix-binary-construction-crash

compiler: Fix type inference bug for bit strings

lib/compiler/src/beam_ssa_type.erl

@@ -2512,6 +2512,24 @@ infer_types_br_1(V, Ts, Ds) ->
             {TrueTypes, FalseTypes}
     end.
 
+infer_relop('=:=', [LHS,RHS],
+            [#t_bitstring{appendable=LHSApp}=LType0,
+             #t_bitstring{appendable=RHSApp}=RType0], Ds)
+  when LHSApp ; RHSApp ->
+    %% Bit strings are special in that nothing about their
+    %% appendable-status can be deduced from a comparison. The only
+    %% information gained is the size_unit. The appendable status is
+    %% unchanged by the comparison.
+    %%
+    %% In order to avoid narrowing the types with regard to
+    %% appendable-status, deduce the types for the case when neither
+    %% LHS or RHS are appendable, then restore the appendable-status.
+    [{LHS,LType},{RHS,RType}|EqTypes] =
+        infer_relop('=:=', [LHS,RHS],
+                    [LType0#t_bitstring{appendable=false},
+                     RType0#t_bitstring{appendable=false}], Ds),
+    [{LHS,LType#t_bitstring{appendable=LHSApp}},
+     {RHS,RType#t_bitstring{appendable=RHSApp}}|EqTypes];
 infer_relop('=:=', [LHS,RHS], [LType,RType], Ds) ->
     EqTypes = infer_eq_type(map_get(LHS, Ds), RType),
 

lib/compiler/test/beam_ssa_check_SUITE_data/appendable.erl

@@ -17,7 +17,7 @@
 %% %CopyrightEnd%
 -module(appendable).
 -export([make_empty/0, t0/0, t1/0, t2/0, t3/0, t4/0,
-	 t5/0, t6/0, t7/0, t8/1, t9/1, t10/1, t11/1, t12/0]).
+	 t5/0, t6/0, t7/0, t8/1, t9/1, t10/1, t11/1, t12/0, t13/0]).
 
 %% Check that just returning an empty bitstring is considered
 %% appendable.
@@ -160,3 +160,12 @@ t12() ->
 
 t12_inner([x|B]) ->
     [x|<<B/binary,1:8>>].
+
+%% Check that the compiler doesn't infer anything about the appendable
+%% status of a bitstring from a comparison.
+t13() ->
+%ssa% () when post_ssa_opt ->
+%ssa% B = bif:binary_part(A, 0, 0),
+%ssa% C = bif:'=:='(B, A) { arg_types => #{ 0 => {t_bitstring,8,false}, 1 => {t_bitstring,256,true}} },
+%ssa% _ = bs_create_bin(append, _, B, ...) { arg_types => #{ 2 => {t_bitstring,256,false} } }.
+   <<(_V4 = binary_part(_V4 = <<0 || _ <- []>>, 0, 0))/bitstring>>.