File 2491-compiler-beam_ssa_alias-Improve-analysis-and-make-it.patch of Package erlang

From 93d1c44fdc976f22660fd4e2cf9ab636e6784c45 Mon Sep 17 00:00:00 2001
From: Frej Drejhammar <frej.drejhammar@gmail.com>
Date: Fri, 23 Feb 2024 11:37:09 +0100
Subject: [PATCH] compiler: beam_ssa_alias: Improve analysis and make it
 deterministic

The best, i.e. least conservative, alias analysis result appears to be
reached when a function's callers are analyzed before the function
itself, i.e. what is needed is a reverse post-order traversal of the
call graph.

This patch corrects an error where exported functions with local
callers could be analyzed before exported functions without local
callers. It also makes the order in which functions are analyzed
deterministic.
---
 lib/compiler/src/beam_ssa_alias.erl | 46 +++++++++++++++++++----------
 1 file changed, 30 insertions(+), 16 deletions(-)

diff --git a/lib/compiler/src/beam_ssa_alias.erl b/lib/compiler/src/beam_ssa_alias.erl
index c0bae90be0..12a3d69f4a 100644
--- a/lib/compiler/src/beam_ssa_alias.erl
+++ b/lib/compiler/src/beam_ssa_alias.erl
@@ -325,7 +325,7 @@ aa(Funs, KillsMap, StMap, FuncDb) ->
 %%%
 aa_fixpoint(Funs, AAS=#aas{alias_map=AliasMap,call_args=CallArgs,
                            func_db=FuncDb}) ->
-    Order = aa_breadth_first(Funs, FuncDb),
+    Order = aa_reverse_post_order(Funs, FuncDb),
     aa_fixpoint(Order, Order, AliasMap, CallArgs, AAS, ?MAX_REPETITIONS).
 
 aa_fixpoint([F|Fs], Order, OldAliasMap, OldCallArgs, AAS0=#aas{st_map=StMap},
@@ -1230,36 +1230,50 @@ aa_make_fun(Dst, Callee=#b_local{name=#b_literal{}},
     AAS = AAS0#aas{call_args=Info,repeats=Repeats},
     {SS, AAS}.
 
-aa_breadth_first(Funs, FuncDb) ->
-    IsExported = fun (F) ->
-                         #{ F := #func_info{exported=E} } = FuncDb,
-                         E
-                 end,
-    Exported = [ F || F <- Funs, IsExported(F)],
-    aa_breadth_first(Exported, [], sets:new([{version,2}]), FuncDb).
+aa_reverse_post_order(Funs, FuncDb) ->
+    %% In order to produce a reverse post order of the call graph, we
+    %% have to make sure all exported functions without local callers
+    %% are visited before exported functions with local callers.
+    IsExportedNoLocalCallers =
+        fun (F) ->
+                #{ F := #func_info{exported=E,in=In} } = FuncDb,
+                E andalso In =:= []
+        end,
+    ExportedNoLocalCallers =
+        lists:sort([ F || F <- Funs, IsExportedNoLocalCallers(F)]),
+    IsExportedLocalCallers =
+        fun (F) ->
+                #{ F := #func_info{exported=E,in=In} } = FuncDb,
+                E andalso In =/= []
+        end,
+    ExportedLocalCallers =
+        lists:sort([ F || F <- Funs, IsExportedLocalCallers(F)]),
+    aa_reverse_post_order(ExportedNoLocalCallers, ExportedLocalCallers,
+                          sets:new([{version,2}]), FuncDb).
 
-aa_breadth_first([F|Work], Next, Seen, FuncDb) ->
+aa_reverse_post_order([F|Work], Next, Seen, FuncDb) ->
     case sets:is_element(F, Seen) of
         true ->
-            aa_breadth_first(Work, Next, Seen, FuncDb);
+            aa_reverse_post_order(Work, Next, Seen, FuncDb);
         false ->
             case FuncDb of
                 #{ F := #func_info{out=Children} } ->
-                    [F|aa_breadth_first(Work, Children ++ Next,
-                                        sets:add_element(F, Seen), FuncDb)];
+                    [F|aa_reverse_post_order(
+                         Work, Children ++ Next,
+                         sets:add_element(F, Seen), FuncDb)];
                 #{} ->
                     %% Other optimization steps can have determined
                     %% that the function is not called and removed it
                     %% from the funcdb, but it still remains in the
                     %% #func_info{} of the (at the syntax-level)
                     %% caller.
-                    aa_breadth_first(Work, Next, Seen, FuncDb)
+                    aa_reverse_post_order(Work, Next, Seen, FuncDb)
             end
     end;
-aa_breadth_first([], [], _Seen, _FuncDb) ->
+aa_reverse_post_order([], [], _Seen, _FuncDb) ->
     [];
-aa_breadth_first([], Next, Seen, FuncDb) ->
-    aa_breadth_first(Next, [], Seen, FuncDb).
+aa_reverse_post_order([], Next, Seen, FuncDb) ->
+    aa_reverse_post_order(Next, [], Seen, FuncDb).
 
 -ifdef(EXTRA_ASSERTS).
 
-- 
2.35.3