File 5121-beam_ssa-Optimize-dominator-calculation.patch of Package erlang

From 33112e74a97ee877eb54a9f54ed01c059cf36965 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 20 Jan 2022 08:43:05 +0100
Subject: [PATCH 1/2] beam_ssa: Optimize dominator calculation

Optimize functions with a huge number of blocks where all blocks are
dominated by block 0. This optimization will make the
`beam_ssa_pre_codegen` pass run more than twice as fast for the
example in #5140.

While at it, clean up indentation in `dom_intersection_1/3`.
---
 lib/compiler/src/beam_ssa.erl | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/lib/compiler/src/beam_ssa.erl b/lib/compiler/src/beam_ssa.erl
index e2688b7fa9..85da3b5937 100644
--- a/lib/compiler/src/beam_ssa.erl
+++ b/lib/compiler/src/beam_ssa.erl
@@ -785,6 +785,9 @@ dom_intersection([S], _Df) ->
 dom_intersection([S|Ss], Df) ->
     dom_intersection(S, Ss, Df).
 
+dom_intersection([0]=S, [_|_], _Df) ->
+    %% No need to continue. (We KNOW that all sets end in [0].)
+    S;
 dom_intersection(S1, [S2|Ss], Df) ->
     dom_intersection(dom_intersection_1(S1, S2, Df), Ss, Df);
 dom_intersection(S, [], _Df) -> S.
@@ -793,11 +796,12 @@ dom_intersection_1([E1|Es1]=Set1, [E2|Es2]=Set2, Df) ->
     %% Blocks are numbered in the order they are found in
     %% reverse postorder.
     #{E1:=Df1,E2:=Df2} = Df,
-    if Df1 > Df2 ->
+    if
+        Df1 > Df2 ->
             dom_intersection_1(Es1, Set2, Df);
-       Df2 > Df1 ->
-            dom_intersection_1(Es2, Set1, Df);  %switch arguments!
-       true ->                                  %Set1 == Set2
+        Df2 > Df1 ->
+            dom_intersection_1(Es2, Set1, Df);  %switch arguments
+        true ->                                  %Set1 == Set2
             %% The common suffix of the sets is the intersection.
             Set1
     end.
-- 
2.31.1