1 files changed, 15 insertions, 3 deletions
diff --git a/lib/compiler/src/beam_ssa_opt.erl b/lib/compiler/src/beam_ssa_opt.erl
index 229edc6a1d..d87c66c272 100644
--- a/lib/compiler/src/beam_ssa_opt.erl
+++ b/lib/compiler/src/beam_ssa_opt.erl
@@ -1939,12 +1939,24 @@ verify_merge_is(_) ->
 
 is_merge_allowed(_, #b_blk{}, #b_blk{is=[#b_set{op=peek_message}|_]}) ->
     false;
-is_merge_allowed(L, #b_blk{last=#b_br{}}=Blk, #b_blk{}) ->
+is_merge_allowed(L, #b_blk{last=#b_br{}}=Blk, #b_blk{is=Is}) ->
     %% The predecessor block must have exactly one successor (L) for
     %% the merge to be safe.
     case beam_ssa:successors(Blk) of
-        [L] -> true;
-        [_|_] -> false
+        [L] ->
+            case Is of
+                [#b_set{op=phi,args=[_]}|_] ->
+                    %% The type optimizer pass must have been
+                    %% turned off, since it would have removed this
+                    %% redundant phi node. Refuse to merge the blocks
+                    %% to ensure that this phi node remains at the
+                    %% beginning of a block.
+                    false;
+                _ ->
+                    true
+            end;
+        [_|_] ->
+            false
     end;
 is_merge_allowed(_, #b_blk{last=#b_switch{}}, #b_blk{}) ->
     false.