Merge branch 'john/erts/disable-unsafe-bs_append-optimization/ERIERL-1177/OTP-19462' into maint-25

* john/erts/disable-unsafe-bs_append-optimization/ERIERL-1177/OTP-19462:
  erts: Disable unsafe optimization in bs_append

Author: Erlang/OTP

erts/emulator/beam/erl_bits.c

@@ -1479,14 +1479,6 @@ erts_bs_append_checked(Process* c_p, Eterm* reg, Uint live,
 	}
     }
 
-    if (build_size_in_bits == 0) {
-        if (HeapWordsLeft(c_p) < extra_words) {
-            (void) erts_garbage_collect(c_p, extra_words, reg, live+1);
-            bin = reg[live];
-        }
-	return bin;
-    }
-
     if((ERTS_UINT_MAX - build_size_in_bits) < erts_bin_offset) {
         c_p->fvalue = am_size;
         c_p->freason = SYSTEM_LIMIT;
@@ -1573,10 +1565,6 @@ erts_bs_append_checked(Process* c_p, Eterm* reg, Uint live,
 	    }
 	}
 
-	if (build_size_in_bits == 0) {
-            return bin;
-	}
-
         if((ERTS_UINT_MAX - build_size_in_bits) < erts_bin_offset) {
             c_p->fvalue = am_size;
             c_p->freason = SYSTEM_LIMIT;

erts/emulator/test/bs_construct_SUITE.erl

@@ -553,9 +553,13 @@ do_something() ->
 
 append_empty_is_same(Config) when is_list(Config) ->
     NonWritableBin = <<"123">>,
-    true = erts_debug:same(NonWritableBin, append(NonWritableBin, <<>>)),
+
+    %% Should use erts_debug:same/2, but this was disabled in PR-9372
+    %% (ERIERL-1177) because the optimization was unsafe.
+    true = NonWritableBin =:= append(NonWritableBin, <<>>),
     WritableBin = <<(id(<<>>))/binary,0,1,2,3,4,5,6,7>>,
-    true = erts_debug:same(WritableBin, append(WritableBin, <<>>)),
+    true = WritableBin =:= append(WritableBin, <<>>),
+
     ok.
 
 append(A, B) ->