From e0065b11830dba9152dfa48d970d601d553f7fc0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 3 Aug 2023 06:45:30 +0200
Subject: [PATCH] beam_jump: Eliminate unsafe sharing of blocks

Fixes #7477
---
 lib/compiler/src/beam_jump.erl       | 38 ++++++++++++++++++----------
 lib/compiler/test/trycatch_SUITE.erl | 12 +++++++++
 2 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/lib/compiler/src/beam_jump.erl b/lib/compiler/src/beam_jump.erl
index 0ca75504cf8c..9536c3073db8 100644
--- a/lib/compiler/src/beam_jump.erl
+++ b/lib/compiler/src/beam_jump.erl
@@ -487,22 +487,26 @@ is_shareable([]) -> true.
 %% branches to them are located.
 %%
 %% If there is more than one scope in the function (that is, if there
-%% try/catch or catch in the function), the scope identifiers will be
-%% added to the line instructions. Recording the scope in the line
-%% instructions makes beam_jump idempotent, ensuring that beam_jump
-%% will not do any unsafe optimizations when when compiling from a .S
-%% file.
+%% is any try/catch or catch in the function), the scope identifiers
+%% will be added to the line instructions. Recording the scope in the
+%% line instructions makes beam_jump idempotent, ensuring that
+%% beam_jump will not do any unsafe optimizations when compiling from
+%% a .S file.
 %%
 
 classify_labels(Is) ->
     classify_labels(Is, 0, #{}).
 
-classify_labels([{'catch',_,_}|Is], Scope, Safe) ->
-    classify_labels(Is, Scope+1, Safe);
+classify_labels([{'catch',_,{f,L}}|Is], Scope0, Safe0) ->
+    Scope = Scope0 + 1,
+    Safe = classify_add_label(L, Scope, Safe0),
+    classify_labels(Is, Scope, Safe);
 classify_labels([{catch_end,_}|Is], Scope, Safe) ->
     classify_labels(Is, Scope+1, Safe);
-classify_labels([{'try',_,_}|Is], Scope, Safe) ->
-    classify_labels(Is, Scope+1, Safe);
+classify_labels([{'try',_,{f,L}}|Is], Scope0, Safe0) ->
+    Scope = Scope0 + 1,
+    Safe = classify_add_label(L, Scope, Safe0),
+    classify_labels(Is, Scope, Safe);
 classify_labels([{'try_end',_}|Is], Scope, Safe) ->
     classify_labels(Is, Scope+1, Safe);
 classify_labels([{'try_case',_}|Is], Scope, Safe) ->
@@ -512,11 +516,7 @@ classify_labels([{'try_case_end',_}|Is], Scope, Safe) ->
 classify_labels([I|Is], Scope, Safe0) ->
     Labels = instr_labels(I),
     Safe = foldl(fun(L, A) ->
-                         case A of
-                             #{L := [Scope]} -> A;
-                             #{L := Other} -> A#{L => ordsets:add_element(Scope, Other)};
-                             #{} -> A#{L => [Scope]}
-                         end
+                         classify_add_label(L, Scope, A)
                  end, Safe0, Labels),
     classify_labels(Is, Scope, Safe);
 classify_labels([], Scope, Safe) ->
@@ -529,6 +529,16 @@ classify_labels([], Scope, Safe) ->
             Safe
     end.
 
+classify_add_label(L, Scope, Map) ->
+    case Map of
+        #{L := [Scope]} ->
+            Map;
+        #{L := [_|_]=Set} ->
+            Map#{L => ordsets:add_element(Scope, Set)};
+        #{} ->
+            Map#{L => [Scope]}
+    end.
+
 %% Eliminate all fallthroughs. Return the result reversed.
 
 eliminate_fallthroughs([{label,L}=Lbl|Is], [I|_]=Acc) ->
diff --git a/lib/compiler/test/trycatch_SUITE.erl b/lib/compiler/test/trycatch_SUITE.erl
index 676b7fffc7fa..4d8b511ee835 100644
--- a/lib/compiler/test/trycatch_SUITE.erl
+++ b/lib/compiler/test/trycatch_SUITE.erl
@@ -1126,6 +1126,8 @@ grab_bag(_Config) ->
 
     {'EXIT',_} = (catch grab_bag_3()),
 
+    true = grab_bag_4(),
+
     ok.
 
 grab_bag_1(V) ->
@@ -1180,6 +1182,16 @@ grab_bag_3() ->
             %% would not return two values as expected.
     end =:= (V0 = 42).
 
+grab_bag_4() ->
+    try
+        erlang:yield()
+    after
+        %% beam_jump would do an unsafe sharing of blocks, resulting
+        %% in an ambiguous_catch_try_state diagnostic from beam_validator.
+        catch <<>> = size(catch ([_ | _] = ok))
+    end.
+
+
 stacktrace(_Config) ->
     V = [make_ref()|self()],
     case ?MODULE:module_info(native) of