From f7fe4573880ce94d794af266d0f37459b7a86709 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 24 May 2019 16:08:55 +0200
Subject: Fix compiler crash in beam_except

The compiler would crash in `beam_except` while compiling this
function:

    bar(Req) ->
      ok = case Req of
        "POST" -> {error, <<"BAD METHOD ", Req/binary>>, Req};
        _ -> ok
      end.

https://bugs.erlang.org/browse/ERL-954
---
 lib/compiler/src/beam_except.erl        |  7 +++++--
 lib/compiler/test/beam_except_SUITE.erl | 20 ++++++++++++++++++--
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/lib/compiler/src/beam_except.erl b/lib/compiler/src/beam_except.erl
index 28c89782c9..2305502800 100644
--- a/lib/compiler/src/beam_except.erl
+++ b/lib/compiler/src/beam_except.erl
@@ -140,8 +140,11 @@ fix_block_1([{set,[],[],{alloc,Live,{F1,F2,Needed0,F3}}}|Is], Words) ->
             [{set,[],[],{alloc,Live,{F1,F2,Needed,F3}}}|Is]
     end;
 fix_block_1([I|Is], Words) ->
-    [I|fix_block_1(Is, Words)].
-
+    [I|fix_block_1(Is, Words)];
+fix_block_1([], _Words) ->
+    %% Rare. The heap allocation was probably done by a binary
+    %% construction instruction.
+    [].
 
 dig_out_fc(Arity, Is0) ->
     Regs0 = maps:from_list([{{x,X},{arg,X}} || X <- seq(0, Arity-1)]),
diff --git a/lib/compiler/test/beam_except_SUITE.erl b/lib/compiler/test/beam_except_SUITE.erl
index 8e3b373d29..67947dc292 100644
--- a/lib/compiler/test/beam_except_SUITE.erl
+++ b/lib/compiler/test/beam_except_SUITE.erl
@@ -21,7 +21,8 @@
 
 -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1,
 	 init_per_group/2,end_per_group/2,
-	 multiple_allocs/1,bs_get_tail/1,coverage/1]).
+	 multiple_allocs/1,bs_get_tail/1,coverage/1,
+         binary_construction_allocation/1]).
 
 suite() -> [{ct_hooks,[ts_install_cth]}].
 
@@ -32,7 +33,8 @@ groups() ->
     [{p,[parallel],
       [multiple_allocs,
        bs_get_tail,
-       coverage]}].
+       coverage,
+       binary_construction_allocation]}].
 
 init_per_suite(Config) ->
     test_lib:recompile(?MODULE),
@@ -118,6 +120,20 @@ coverage(_) ->
 
 fake_function_clause(A) -> error(function_clause, [A,42.0]).
 
+
+binary_construction_allocation(_Config) ->
+    ok = do_binary_construction_allocation("PUT"),
+    ok.
+
+do_binary_construction_allocation(Req) ->
+    %% Allocation for building the error term was done by the
+    %% bs_init2 instruction. beam_except crashed because it expected
+    %% an explicit allocation instruction.
+    ok = case Req of
+             "POST" -> {error, <<"BAD METHOD ", Req/binary>>, Req};
+             _ -> ok
+         end.
+
 id(I) -> I.
 
 -file("fake.erl", 1).
-- 
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