From 203fdc9d70d41efd3e16ea4e0bacedb647d70ac9 Mon Sep 17 00:00:00 2001
From: Frej Drejhammar <frej.drejhammar@gmail.com>
Date: Tue, 23 Jul 2024 14:11:12 +0200
Subject: [PATCH] compiler alias analysis: Alternate function traversal order

Sharing state information flows from callers to callees for function
arguments, and from callees to callers for results. Previously callers
were always analyzed before callees, but it turns out that the alias
analysis converges faster if the traversal order is alternated between
caller-callee and callee-caller.
---
 lib/compiler/src/beam_ssa_alias.erl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/compiler/src/beam_ssa_alias.erl b/lib/compiler/src/beam_ssa_alias.erl
index aab967b76897..0f9e407949d7 100644
--- a/lib/compiler/src/beam_ssa_alias.erl
+++ b/lib/compiler/src/beam_ssa_alias.erl
@@ -354,7 +354,7 @@ aa_fixpoint(Funs, AAS=#aas{func_db=FuncDb}) ->
     Order = aa_order(Funs, FuncDb),
     ?DP("Traversal order:~n  ~s~n",
         [string:join([fn(F) || F <- Order], ",\n  ")]),
-    aa_fixpoint(Order, Order, AAS, 1).
+    aa_fixpoint(Order, reverse(Order), AAS, 1).
 
 aa_fixpoint([F|Fs], Order,
             AAS0=#aas{func_db=FuncDb,st_map=StMap,
@@ -388,7 +388,7 @@ aa_fixpoint([], Order, #aas{func_db=FuncDb,repeats=Repeats}=AAS, NoofIters) ->
             {StMap, FuncDb};
         NewOrder ->
             ?DP("**** Starting traversal ~p ****~n", [NoofIters + 1]),
-            aa_fixpoint(NewOrder, Order,
+            aa_fixpoint(NewOrder, reverse(Order),
                         AAS#aas{repeats=sets:new()}, NoofIters + 1)
     end.