From d0dc1ebc5da30f67cd8a8f9abe5f5a2c8742f681 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Wed, 20 Mar 2024 08:24:03 +0100
Subject: [PATCH] Fix failing binary match

Closes #8280
---
 lib/compiler/src/beam_ssa_codegen.erl |  4 ++++
 lib/compiler/src/beam_ssa_opt.erl     | 13 +++++++++++--
 lib/compiler/test/bs_match_SUITE.erl  |  8 ++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/lib/compiler/src/beam_ssa_codegen.erl b/lib/compiler/src/beam_ssa_codegen.erl
index 6f6de9996268..7879861c097e 100644
--- a/lib/compiler/src/beam_ssa_codegen.erl
+++ b/lib/compiler/src/beam_ssa_codegen.erl
@@ -2260,6 +2260,10 @@ bs_translate([]) -> [].
 
 bs_translate_collect([I|Is]=Is0, Ctx, Fail, Acc) ->
     case bs_translate_instr(I) of
+        {Ctx,_,{ensure_at_least,_,_}} ->
+            %% There should only be a single `ensure_at_least`
+            %% instruction in each `bs_match` instruction.
+            {bs_translate_fixup(Acc),Fail,Is0};
         {Ctx,Fail,Instr} ->
             bs_translate_collect(Is, Ctx, Fail, [Instr|Acc]);
         {Ctx,{f,0},Instr} ->
diff --git a/lib/compiler/src/beam_ssa_opt.erl b/lib/compiler/src/beam_ssa_opt.erl
index 13e4114319db..0be627760535 100644
--- a/lib/compiler/src/beam_ssa_opt.erl
+++ b/lib/compiler/src/beam_ssa_opt.erl
@@ -304,8 +304,8 @@ late_epilogue_passes(Opts) ->
           ?PASS(ssa_opt_sink),
           ?PASS(ssa_opt_blockify),
           ?PASS(ssa_opt_redundant_br),
-          ?PASS(ssa_opt_bs_ensure),
           ?PASS(ssa_opt_merge_blocks),
+          ?PASS(ssa_opt_bs_ensure),
           ?PASS(ssa_opt_try),
           ?PASS(ssa_opt_get_tuple_element),
           ?PASS(ssa_opt_tail_literals),
@@ -3325,7 +3325,7 @@ redundant_br_safe_bool(Is, Bool) ->
     end.
 
 %%%
-%%% Add the bs_ensure instruction before a sequence of `bs_match`
+%%% Add the `bs_ensure` instruction before a sequence of `bs_match`
 %%% (SSA) instructions, each having a literal size and the
 %%% same failure label.
 %%%
@@ -3333,6 +3333,15 @@ redundant_br_safe_bool(Is, Bool) ->
 %%% instruction that can match multiple segments having the same
 %%% failure label.
 %%%
+%%% It is beneficial but not essential to run this pass after
+%%% the `merge_blocks/1` pass. For the following example, two separate
+%%% `bs_match/1` instructions will emitted if blocks have not been
+%%% merged before this pass:
+%%%
+%%%    A = 0,
+%%%    B = <<1, 2, 3>>,
+%%%    <<A, B:(byte_size(B))/binary>> = <<0, 1, 2, 3>>
+%%%
 
 ssa_opt_bs_ensure({#opt_st{ssa=Blocks0,cnt=Count0}=St, FuncDb}) when is_map(Blocks0) ->
     RPO = beam_ssa:rpo(Blocks0),
diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
index b24f1afdd8e5..45c3ab04a9e5 100644
--- a/lib/compiler/test/bs_match_SUITE.erl
+++ b/lib/compiler/test/bs_match_SUITE.erl
@@ -2724,6 +2724,8 @@ bs_match(_Config) ->
 
     {'EXIT',{{badmatch,<<>>},_}} = catch do_bs_match_gh_7467(<<>>),
 
+    {0,<<1,2,3>>} = do_bs_match_gh_8280(),
+
     ok.
 
 do_bs_match_1(_, X) ->
@@ -2798,6 +2800,12 @@ do_bs_match_gh_6755(B) ->
 do_bs_match_gh_7467(A) ->
     do_bs_match_gh_7467(<<_:1/bits>> = A).
 
+do_bs_match_gh_8280() ->
+    A = 0,
+    B = <<1, 2, 3>>,
+    <<A, B:(byte_size(B))/binary>> = id(<<0, 1, 2, 3>>),
+    {A, B}.
+
 %% GH-6348/OTP-18297: Allow aliases for binaries.
 -record(ba_foo, {a,b,c}).