Merge branch 'maint'

* maint:
  Update primary bootstrap
  beam_block: Fix potentially unsafe optimization in move_allocates/1

66 files changed, 91 insertions, 40 deletions

diff --git a/bootstrap/bin/start.boot b/bootstrap/bin/start.boot
index 295c805ea8..4a1f656c3c 100644
--- a/bootstrap/bin/start.boot
+++ b/bootstrap/bin/start.boot
diff --git a/bootstrap/bin/start_clean.boot b/bootstrap/bin/start_clean.boot
index 295c805ea8..4a1f656c3c 100644
--- a/bootstrap/bin/start_clean.boot
+++ b/bootstrap/bin/start_clean.boot
diff --git a/bootstrap/lib/compiler/ebin/beam_asm.beam b/bootstrap/lib/compiler/ebin/beam_asm.beam
index 38b3c31cab..481d43c967 100644
--- a/bootstrap/lib/compiler/ebin/beam_asm.beam
+++ b/bootstrap/lib/compiler/ebin/beam_asm.beam
diff --git a/bootstrap/lib/compiler/ebin/beam_block.beam b/bootstrap/lib/compiler/ebin/beam_block.beam
index ea91a62b56..b6a4b6f10f 100644
--- a/bootstrap/lib/compiler/ebin/beam_block.beam
+++ b/bootstrap/lib/compiler/ebin/beam_block.beam
diff --git a/bootstrap/lib/compiler/ebin/beam_bool.beam b/bootstrap/lib/compiler/ebin/beam_bool.beam
index 1673c4aadb..37f368190e 100644
--- a/bootstrap/lib/compiler/ebin/beam_bool.beam
+++ b/bootstrap/lib/compiler/ebin/beam_bool.beam
diff --git a/bootstrap/lib/compiler/ebin/beam_bsm.beam b/bootstrap/lib/compiler/ebin/beam_bsm.beam
index 51abd68b00..48e8f80f79 100644
--- a/bootstrap/lib/compiler/ebin/beam_bsm.beam
+++ b/bootstrap/lib/compiler/ebin/beam_bsm.beam
diff --git a/bootstrap/lib/compiler/ebin/beam_clean.beam b/bootstrap/lib/compiler/ebin/beam_clean.beam
index 0f24e040e3..ed0827953c 100644
--- a/bootstrap/lib/compiler/ebin/beam_clean.beam
+++ b/bootstrap/lib/compiler/ebin/beam_clean.beam
diff --git a/bootstrap/lib/compiler/ebin/beam_validator.beam b/bootstrap/lib/compiler/ebin/beam_validator.beam
index fcb2202d2a..9d952f0a64 100644
--- a/bootstrap/lib/compiler/ebin/beam_validator.beam
+++ b/bootstrap/lib/compiler/ebin/beam_validator.beam
diff --git a/bootstrap/lib/compiler/ebin/cerl.beam b/bootstrap/lib/compiler/ebin/cerl.beam
index dea6cb4ee2..eecdd4e2dd 100644
--- a/bootstrap/lib/compiler/ebin/cerl.beam
+++ b/bootstrap/lib/compiler/ebin/cerl.beam
diff --git a/bootstrap/lib/compiler/ebin/compile.beam b/bootstrap/lib/compiler/ebin/compile.beam
index da62dd7191..044ed03d93 100644
--- a/bootstrap/lib/compiler/ebin/compile.beam
+++ b/bootstrap/lib/compiler/ebin/compile.beam
diff --git a/bootstrap/lib/compiler/ebin/compiler.app b/bootstrap/lib/compiler/ebin/compiler.app
index 283fcb7478..ebd5205219 100644
--- a/bootstrap/lib/compiler/ebin/compiler.app
+++ b/bootstrap/lib/compiler/ebin/compiler.app
@@ -19,7 +19,7 @@
 
 {application, compiler,
  [{description, "ERTS  CXC 138 10"},
-  {vsn, "7.0"},
+  {vsn, "7.0.1"},
   {modules, [
 	     beam_a,
 	     beam_asm,
diff --git a/bootstrap/lib/compiler/ebin/core_lint.beam b/bootstrap/lib/compiler/ebin/core_lint.beam
index 0e47e00b15..47f9f53546 100644
--- a/bootstrap/lib/compiler/ebin/core_lint.beam
+++ b/bootstrap/lib/compiler/ebin/core_lint.beam
diff --git a/bootstrap/lib/compiler/ebin/core_parse.beam b/bootstrap/lib/compiler/ebin/core_parse.beam
index 920dbc922f..2599138a8c 100644
--- a/bootstrap/lib/compiler/ebin/core_parse.beam
+++ b/bootstrap/lib/compiler/ebin/core_parse.beam
diff --git a/bootstrap/lib/compiler/ebin/core_scan.beam b/bootstrap/lib/compiler/ebin/core_scan.beam
index 5f7b22ba8b..3017a4e026 100644
--- a/bootstrap/lib/compiler/ebin/core_scan.beam
+++ b/bootstrap/lib/compiler/ebin/core_scan.beam
diff --git a/bootstrap/lib/compiler/ebin/sys_core_fold.beam b/bootstrap/lib/compiler/ebin/sys_core_fold.beam
index 68cc4e3ff3..75a6570461 100644
--- a/bootstrap/lib/compiler/ebin/sys_core_fold.beam
+++ b/bootstrap/lib/compiler/ebin/sys_core_fold.beam
diff --git a/bootstrap/lib/compiler/ebin/v3_core.beam b/bootstrap/lib/compiler/ebin/v3_core.beam
index e8e120e145..54f507218f 100644
--- a/bootstrap/lib/compiler/ebin/v3_core.beam
+++ b/bootstrap/lib/compiler/ebin/v3_core.beam
diff --git a/bootstrap/lib/compiler/ebin/v3_kernel.beam b/bootstrap/lib/compiler/ebin/v3_kernel.beam
index 47eaf3b5e8..60cc6503eb 100644
--- a/bootstrap/lib/compiler/ebin/v3_kernel.beam
+++ b/bootstrap/lib/compiler/ebin/v3_kernel.beam
diff --git a/bootstrap/lib/compiler/ebin/v3_life.beam b/bootstrap/lib/compiler/ebin/v3_life.beam
index b220e475ee..d4b3f2a5e6 100644
--- a/bootstrap/lib/compiler/ebin/v3_life.beam
+++ b/bootstrap/lib/compiler/ebin/v3_life.beam
diff --git a/bootstrap/lib/kernel/ebin/application_controller.beam b/bootstrap/lib/kernel/ebin/application_controller.beam
index 2b3c8cf454..d46de4527a 100644
--- a/bootstrap/lib/kernel/ebin/application_controller.beam
+++ b/bootstrap/lib/kernel/ebin/application_controller.beam
diff --git a/bootstrap/lib/kernel/ebin/application_master.beam b/bootstrap/lib/kernel/ebin/application_master.beam
index 24492a6771..da770c5a84 100644
--- a/bootstrap/lib/kernel/ebin/application_master.beam
+++ b/bootstrap/lib/kernel/ebin/application_master.beam
diff --git a/bootstrap/lib/kernel/ebin/auth.beam b/bootstrap/lib/kernel/ebin/auth.beam
index cbe477830b..1ccad1a5a3 100644
--- a/bootstrap/lib/kernel/ebin/auth.beam
+++ b/bootstrap/lib/kernel/ebin/auth.beam
diff --git a/bootstrap/lib/kernel/ebin/code_server.beam b/bootstrap/lib/kernel/ebin/code_server.beam
index 6f99487ca7..7f073fe932 100644
--- a/bootstrap/lib/kernel/ebin/code_server.beam
+++ b/bootstrap/lib/kernel/ebin/code_server.beam
diff --git a/bootstrap/lib/kernel/ebin/disk_log.beam b/bootstrap/lib/kernel/ebin/disk_log.beam
index 5aa8bf7dc1..31fb2d609d 100644
--- a/bootstrap/lib/kernel/ebin/disk_log.beam
+++ b/bootstrap/lib/kernel/ebin/disk_log.beam
diff --git a/bootstrap/lib/kernel/ebin/disk_log_1.beam b/bootstrap/lib/kernel/ebin/disk_log_1.beam
index cb627c10a5..6b10d652de 100644
--- a/bootstrap/lib/kernel/ebin/disk_log_1.beam
+++ b/bootstrap/lib/kernel/ebin/disk_log_1.beam
diff --git a/bootstrap/lib/kernel/ebin/disk_log_server.beam b/bootstrap/lib/kernel/ebin/disk_log_server.beam
index 50154045be..67cda715c4 100644
--- a/bootstrap/lib/kernel/ebin/disk_log_server.beam
+++ b/bootstrap/lib/kernel/ebin/disk_log_server.beam
diff --git a/bootstrap/lib/kernel/ebin/dist_ac.beam b/bootstrap/lib/kernel/ebin/dist_ac.beam
index d2c186f03a..56868dfe6d 100644
--- a/bootstrap/lib/kernel/ebin/dist_ac.beam
+++ b/bootstrap/lib/kernel/ebin/dist_ac.beam
diff --git a/bootstrap/lib/kernel/ebin/dist_util.beam b/bootstrap/lib/kernel/ebin/dist_util.beam
index eb09a06785..e5d0f66e6e 100644
--- a/bootstrap/lib/kernel/ebin/dist_util.beam
+++ b/bootstrap/lib/kernel/ebin/dist_util.beam
diff --git a/bootstrap/lib/kernel/ebin/erl_epmd.beam b/bootstrap/lib/kernel/ebin/erl_epmd.beam
index 8e8460514c..19be6babd1 100644
--- a/bootstrap/lib/kernel/ebin/erl_epmd.beam
+++ b/bootstrap/lib/kernel/ebin/erl_epmd.beam
diff --git a/bootstrap/lib/kernel/ebin/global.beam b/bootstrap/lib/kernel/ebin/global.beam
index 465dab3a52..601cb9176b 100644
--- a/bootstrap/lib/kernel/ebin/global.beam
+++ b/bootstrap/lib/kernel/ebin/global.beam
diff --git a/bootstrap/lib/kernel/ebin/global_group.beam b/bootstrap/lib/kernel/ebin/global_group.beam
index 03202f68eb..8bd51c2424 100644
--- a/bootstrap/lib/kernel/ebin/global_group.beam
+++ b/bootstrap/lib/kernel/ebin/global_group.beam
diff --git a/bootstrap/lib/kernel/ebin/group.beam b/bootstrap/lib/kernel/ebin/group.beam
index 38eb0e7a6c..c2c66f77ec 100644
--- a/bootstrap/lib/kernel/ebin/group.beam
+++ b/bootstrap/lib/kernel/ebin/group.beam
diff --git a/bootstrap/lib/kernel/ebin/heart.beam b/bootstrap/lib/kernel/ebin/heart.beam
index 86044153af..2ab7ef9d9f 100644
--- a/bootstrap/lib/kernel/ebin/heart.beam
+++ b/bootstrap/lib/kernel/ebin/heart.beam
diff --git a/bootstrap/lib/kernel/ebin/inet.beam b/bootstrap/lib/kernel/ebin/inet.beam
index 5ae4090a61..ff7f0ba7e6 100644
--- a/bootstrap/lib/kernel/ebin/inet.beam
+++ b/bootstrap/lib/kernel/ebin/inet.beam
diff --git a/bootstrap/lib/kernel/ebin/inet_res.beam b/bootstrap/lib/kernel/ebin/inet_res.beam
index 2713c7fef6..b1bbf771a3 100644
--- a/bootstrap/lib/kernel/ebin/inet_res.beam
+++ b/bootstrap/lib/kernel/ebin/inet_res.beam
diff --git a/bootstrap/lib/kernel/ebin/inet_tcp_dist.beam b/bootstrap/lib/kernel/ebin/inet_tcp_dist.beam
index d06bdf709a..5fd6b3e909 100644
--- a/bootstrap/lib/kernel/ebin/inet_tcp_dist.beam
+++ b/bootstrap/lib/kernel/ebin/inet_tcp_dist.beam
diff --git a/bootstrap/lib/kernel/ebin/kernel_config.beam b/bootstrap/lib/kernel/ebin/kernel_config.beam
index 8379f77e94..5e59fc2f82 100644
--- a/bootstrap/lib/kernel/ebin/kernel_config.beam
+++ b/bootstrap/lib/kernel/ebin/kernel_config.beam
diff --git a/bootstrap/lib/kernel/ebin/net_kernel.beam b/bootstrap/lib/kernel/ebin/net_kernel.beam
index 8afe1c0388..6cf6916fe6 100644
--- a/bootstrap/lib/kernel/ebin/net_kernel.beam
+++ b/bootstrap/lib/kernel/ebin/net_kernel.beam
diff --git a/bootstrap/lib/kernel/ebin/user.beam b/bootstrap/lib/kernel/ebin/user.beam
index c2b2808555..cded4b87be 100644
--- a/bootstrap/lib/kernel/ebin/user.beam
+++ b/bootstrap/lib/kernel/ebin/user.beam
diff --git a/bootstrap/lib/kernel/ebin/user_drv.beam b/bootstrap/lib/kernel/ebin/user_drv.beam
index 1d72927105..bd9b1a3bce 100644
--- a/bootstrap/lib/kernel/ebin/user_drv.beam
+++ b/bootstrap/lib/kernel/ebin/user_drv.beam
diff --git a/bootstrap/lib/kernel/ebin/wrap_log_reader.beam b/bootstrap/lib/kernel/ebin/wrap_log_reader.beam
index 91ef523b99..93f1f1ba72 100644
--- a/bootstrap/lib/kernel/ebin/wrap_log_reader.beam
+++ b/bootstrap/lib/kernel/ebin/wrap_log_reader.beam
diff --git a/bootstrap/lib/stdlib/ebin/binary.beam b/bootstrap/lib/stdlib/ebin/binary.beam
index 538d169565..ff9022388e 100644
--- a/bootstrap/lib/stdlib/ebin/binary.beam
+++ b/bootstrap/lib/stdlib/ebin/binary.beam
diff --git a/bootstrap/lib/stdlib/ebin/dets.beam b/bootstrap/lib/stdlib/ebin/dets.beam
index 0dfaca7a48..8b9049c855 100644
--- a/bootstrap/lib/stdlib/ebin/dets.beam
+++ b/bootstrap/lib/stdlib/ebin/dets.beam
diff --git a/bootstrap/lib/stdlib/ebin/dets_server.beam b/bootstrap/lib/stdlib/ebin/dets_server.beam
index 502eb98318..0b0783bf9d 100644
--- a/bootstrap/lib/stdlib/ebin/dets_server.beam
+++ b/bootstrap/lib/stdlib/ebin/dets_server.beam
diff --git a/bootstrap/lib/stdlib/ebin/dets_utils.beam b/bootstrap/lib/stdlib/ebin/dets_utils.beam
index 37247c7176..2a3b22b7e0 100644
--- a/bootstrap/lib/stdlib/ebin/dets_utils.beam
+++ b/bootstrap/lib/stdlib/ebin/dets_utils.beam
diff --git a/bootstrap/lib/stdlib/ebin/dets_v8.beam b/bootstrap/lib/stdlib/ebin/dets_v8.beam
index 9a1416a316..39ddeebf85 100644
--- a/bootstrap/lib/stdlib/ebin/dets_v8.beam
+++ b/bootstrap/lib/stdlib/ebin/dets_v8.beam
diff --git a/bootstrap/lib/stdlib/ebin/epp.beam b/bootstrap/lib/stdlib/ebin/epp.beam
index 5bcc7cf8d9..b1a75a54eb 100644
--- a/bootstrap/lib/stdlib/ebin/epp.beam
+++ b/bootstrap/lib/stdlib/ebin/epp.beam
diff --git a/bootstrap/lib/stdlib/ebin/erl_lint.beam b/bootstrap/lib/stdlib/ebin/erl_lint.beam
index ebe80a32a8..6653cb9f49 100644
--- a/bootstrap/lib/stdlib/ebin/erl_lint.beam
+++ b/bootstrap/lib/stdlib/ebin/erl_lint.beam
diff --git a/bootstrap/lib/stdlib/ebin/erl_parse.beam b/bootstrap/lib/stdlib/ebin/erl_parse.beam
index 33a0753965..d75b490162 100644
--- a/bootstrap/lib/stdlib/ebin/erl_parse.beam
+++ b/bootstrap/lib/stdlib/ebin/erl_parse.beam
diff --git a/bootstrap/lib/stdlib/ebin/erl_pp.beam b/bootstrap/lib/stdlib/ebin/erl_pp.beam
index e845392e4b..c8798a6094 100644
--- a/bootstrap/lib/stdlib/ebin/erl_pp.beam
+++ b/bootstrap/lib/stdlib/ebin/erl_pp.beam
diff --git a/bootstrap/lib/stdlib/ebin/file_sorter.beam b/bootstrap/lib/stdlib/ebin/file_sorter.beam
index 03d9020bb5..693c0b523d 100644
--- a/bootstrap/lib/stdlib/ebin/file_sorter.beam
+++ b/bootstrap/lib/stdlib/ebin/file_sorter.beam
diff --git a/bootstrap/lib/stdlib/ebin/gen_fsm.beam b/bootstrap/lib/stdlib/ebin/gen_fsm.beam
index 595574585b..0370d430b2 100644
--- a/bootstrap/lib/stdlib/ebin/gen_fsm.beam
+++ b/bootstrap/lib/stdlib/ebin/gen_fsm.beam
diff --git a/bootstrap/lib/stdlib/ebin/gen_server.beam b/bootstrap/lib/stdlib/ebin/gen_server.beam
index 3097207512..aa22d6aae4 100644
--- a/bootstrap/lib/stdlib/ebin/gen_server.beam
+++ b/bootstrap/lib/stdlib/ebin/gen_server.beam
diff --git a/bootstrap/lib/stdlib/ebin/log_mf_h.beam b/bootstrap/lib/stdlib/ebin/log_mf_h.beam
index 0c4b22c3df..d0e18955c7 100644
--- a/bootstrap/lib/stdlib/ebin/log_mf_h.beam
+++ b/bootstrap/lib/stdlib/ebin/log_mf_h.beam
diff --git a/bootstrap/lib/stdlib/ebin/pool.beam b/bootstrap/lib/stdlib/ebin/pool.beam
index a06ae1717a..cc6e536ccd 100644
--- a/bootstrap/lib/stdlib/ebin/pool.beam
+++ b/bootstrap/lib/stdlib/ebin/pool.beam
diff --git a/bootstrap/lib/stdlib/ebin/qlc.beam b/bootstrap/lib/stdlib/ebin/qlc.beam
index fa3240810d..a39ca1391b 100644
--- a/bootstrap/lib/stdlib/ebin/qlc.beam
+++ b/bootstrap/lib/stdlib/ebin/qlc.beam
diff --git a/bootstrap/lib/stdlib/ebin/qlc_pt.beam b/bootstrap/lib/stdlib/ebin/qlc_pt.beam
index 4a065ec57f..e9c760ba45 100644
--- a/bootstrap/lib/stdlib/ebin/qlc_pt.beam
+++ b/bootstrap/lib/stdlib/ebin/qlc_pt.beam
diff --git a/bootstrap/lib/stdlib/ebin/shell.beam b/bootstrap/lib/stdlib/ebin/shell.beam
index b0c98f4b98..3d7b53387b 100644
--- a/bootstrap/lib/stdlib/ebin/shell.beam
+++ b/bootstrap/lib/stdlib/ebin/shell.beam
diff --git a/bootstrap/lib/stdlib/ebin/slave.beam b/bootstrap/lib/stdlib/ebin/slave.beam
index 373d65f198..fa0fa8c960 100644
--- a/bootstrap/lib/stdlib/ebin/slave.beam
+++ b/bootstrap/lib/stdlib/ebin/slave.beam
diff --git a/bootstrap/lib/stdlib/ebin/sofs.beam b/bootstrap/lib/stdlib/ebin/sofs.beam
index 5099d4ecc0..7b8ab95876 100644
--- a/bootstrap/lib/stdlib/ebin/sofs.beam
+++ b/bootstrap/lib/stdlib/ebin/sofs.beam
diff --git a/bootstrap/lib/stdlib/ebin/stdlib.app b/bootstrap/lib/stdlib/ebin/stdlib.app
index ceb55c66fc..81b30526ab 100644
--- a/bootstrap/lib/stdlib/ebin/stdlib.app
+++ b/bootstrap/lib/stdlib/ebin/stdlib.app
@@ -20,7 +20,7 @@
 %%
 {application, stdlib,
  [{description, "ERTS  CXC 138 10"},
-  {vsn, "3.0"},
+  {vsn, "3.0.1"},
   {modules, [array,
 	     base64,
 	     beam_lib,
diff --git a/bootstrap/lib/stdlib/ebin/stdlib.appup b/bootstrap/lib/stdlib/ebin/stdlib.appup
index 737486d3c5..322a329931 100644
--- a/bootstrap/lib/stdlib/ebin/stdlib.appup
+++ b/bootstrap/lib/stdlib/ebin/stdlib.appup
@@ -16,7 +16,7 @@
 %% limitations under the License.
 %%
 %% %CopyrightEnd%
-{"3.0",
+{"3.0.1",
  %% Up from - max one major revision back
  [{<<"3\\.0(\\.[0-9]+)*">>,[restart_new_emulator]},       % OTP-19.*
   {<<"2\\.[5-8](\\.[0-9]+)*">>,[restart_new_emulator]}],  % OTP-18.*
diff --git a/bootstrap/lib/stdlib/ebin/supervisor.beam b/bootstrap/lib/stdlib/ebin/supervisor.beam
index 3ae911ab29..c7534b5438 100644
--- a/bootstrap/lib/stdlib/ebin/supervisor.beam
+++ b/bootstrap/lib/stdlib/ebin/supervisor.beam
diff --git a/bootstrap/lib/stdlib/ebin/supervisor_bridge.beam b/bootstrap/lib/stdlib/ebin/supervisor_bridge.beam
index d2bfe6eea8..f52d5c407b 100644
--- a/bootstrap/lib/stdlib/ebin/supervisor_bridge.beam
+++ b/bootstrap/lib/stdlib/ebin/supervisor_bridge.beam
diff --git a/bootstrap/lib/stdlib/ebin/zip.beam b/bootstrap/lib/stdlib/ebin/zip.beam
index 6ef3732965..919166fe89 100644
--- a/bootstrap/lib/stdlib/ebin/zip.beam
+++ b/bootstrap/lib/stdlib/ebin/zip.beam
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index 85d332c56e..ec41925beb 100644
--- a/lib/compiler/src/beam_block.erl
+++ b/lib/compiler/src/beam_block.erl
@@ -159,14 +159,43 @@ find_fixpoint(OptFun, Is0) ->
     end.
 
 %% move_allocates(Is0) -> Is
-%%  Move allocate instructions upwards in the instruction stream, in the
-%%  hope of getting more possibilities for optimizing away moves later.
+%%  Move allocate instructions upwards in the instruction stream
+%%  (within the same block), in the hope of getting more possibilities
+%%  for optimizing away moves later.
 %%
-%%  NOTE: Moving allocation instructions is only safe because it is done
-%%  immediately after code generation so that we KNOW that if {x,X} is
-%%  initialized, all x registers with lower numbers are also initialized.
-%%  That assumption may not be true after other optimizations, such as
-%%  the beam_utils:live_opt/1 optimization.
+%%  For example, we can transform the following instructions:
+%%
+%%     get_tuple_element x(1) Element => x(2)
+%%     allocate_zero StackSize 3    %% x(0), x(1), x(2) are live
+%%
+%%  to the following instructions:
+%%
+%%     allocate_zero StackSize 2    %% x(0) and x(1) are live
+%%     get_tuple_element x(1) Element => x(2)
+%%
+%%  NOTE: Since the beam_reorder pass has been run, it is no longer
+%%  safe to assume that if x(N) is initialized, then all lower-numbered
+%%  x registers are also initialized.
+%%
+%%  For example, in general it is not safe to transform the following
+%%  instructions:
+%%
+%%     get_tuple_element x(0) Element => x(1)
+%%     allocate_zero StackSize 3    %x(0), x(1), x(2) are live
+%%
+%%  to the following instructions:
+%%
+%%     allocate_zero StackSize 3
+%%     get_tuple_element x(0) Element => x(1)
+%%
+%%  The transformation is safe if and only if x(1) has been
+%%  initialized previously. Unfortunately, beam_reorder may have moved
+%%  a get_tuple_element instruction so that x(1) is not always
+%%  initialized when this code is reached. To find whether or not x(1)
+%%  is initialized, we would need to analyze all code preceding these
+%%  two instructions (across branches). Since we currently don't have
+%%  any practical mechanism for doing that, we will have to
+%%  conservatively assume that the transformation is unsafe.
 
 move_allocates([{block,Bl0}|Is]) ->
     Bl = move_allocates_1(reverse(Bl0), []),
@@ -175,27 +204,19 @@ move_allocates([I|Is]) ->
     [I|move_allocates(Is)];
 move_allocates([]) -> [].
 
-move_allocates_1([{set,[],[],{alloc,_,_}=Alloc}|Is0], Acc0) ->
-    {Is,Acc} = move_allocates_2(Alloc, Is0, Acc0),
-    move_allocates_1(Is, Acc);
+move_allocates_1([I|Is], [{set,[],[],{alloc,Live0,Info}}|Acc]=Acc0) ->
+    case {alloc_may_pass(I),alloc_live_regs(I, Live0)} of
+	{false,_} ->
+	    move_allocates_1(Is, [I|Acc0]);
+	{true,not_possible} ->
+	    move_allocates_1(Is, [I|Acc0]);
+	{true,Live} when is_integer(Live) ->
+	    A = {set,[],[],{alloc,Live,Info}},
+	    move_allocates_1(Is, [A,I|Acc])
+    end;
 move_allocates_1([I|Is], Acc) ->
     move_allocates_1(Is, [I|Acc]);
-move_allocates_1([], Is) -> Is.
-
-move_allocates_2({alloc,Live,Info}, [{set,[],[],{alloc,Live0,Info0}}|Is], Acc) ->
-    Live = Live0,				% Assertion.
-    Alloc = {alloc,Live,combine_alloc(Info0, Info)},
-    move_allocates_2(Alloc, Is, Acc);
-move_allocates_2({alloc,Live,Info}=Alloc0, [I|Is]=Is0, Acc) ->
-    case alloc_may_pass(I) of
-	false ->
-	    {Is0,[{set,[],[],Alloc0}|Acc]};
-	true ->
-	    Alloc = {alloc,alloc_live_regs(I, Live),Info},
-	    move_allocates_2(Alloc, Is, [I|Acc])
-    end;
-move_allocates_2(Alloc, [], Acc) ->
-    {[],[{set,[],[],Alloc}|Acc]}.
+move_allocates_1([], Acc) -> Acc.
 
 alloc_may_pass({set,_,_,{alloc,_,_}}) -> false;
 alloc_may_pass({set,_,_,{set_tuple_element,_}}) -> false;
@@ -204,9 +225,6 @@ alloc_may_pass({set,_,_,put_list}) -> false;
 alloc_may_pass({set,_,_,put}) -> false;
 alloc_may_pass({set,_,_,_}) -> true.
     
-combine_alloc({_,Ns,Nh1,Init}, {_,nostack,Nh2,[]})  ->
-    {zero,Ns,beam_utils:combine_heap_needs(Nh1, Nh2),Init}.
-
 %% opt([Instruction]) -> [Instruction]
 %%  Optimize the instruction stream inside a basic block.
 
@@ -393,10 +411,19 @@ eliminate_use_of_from_reg([I]=Is, From, _To, Acc) ->
 %% opt_alloc(Instructions) -> Instructions'
 %%  Optimises all allocate instructions.
 
+opt_alloc([{set,[],[],{alloc,Live0,Info0}},
+	   {set,[],[],{alloc,Live,Info}}|Is]) ->
+    Live = Live0,				%Assertion.
+    Alloc = combine_alloc(Info0, Info),
+    I = {set,[],[],{alloc,Live,Alloc}},
+    opt_alloc([I|Is]);
 opt_alloc([{set,[],[],{alloc,R,{_,Ns,Nh,[]}}}|Is]) ->
     [{set,[],[],opt_alloc(Is, Ns, Nh, R)}|Is];
 opt_alloc([I|Is]) -> [I|opt_alloc(Is)];
 opt_alloc([]) -> [].
+
+combine_alloc({_,Ns,Nh1,Init}, {_,nostack,Nh2,[]})  ->
+    {zero,Ns,beam_utils:combine_heap_needs(Nh1, Nh2),Init}.
 	
 %% opt_alloc(Instructions, FrameSize, HeapNeed, LivingRegs) -> [Instr]
 %%  Generates the optimal sequence of instructions for
@@ -445,13 +472,14 @@ count_ones(Bits, Acc) ->
 
 alloc_live_regs({set,Ds,Ss,_}, Regs0) ->
     Rset = x_live(Ss, x_dead(Ds, (1 bsl Regs0)-1)),
-    live_regs(Rset).
+    live_regs(0, Rset).
 
-live_regs(Regs) ->
-    live_regs_1(0, Regs).
-
-live_regs_1(N, 0) -> N;
-live_regs_1(N, Regs) -> live_regs_1(N+1, Regs bsr 1).
+live_regs(N, 0) ->
+    N;
+live_regs(N, Regs) when Regs band 1 =:= 1 ->
+    live_regs(N+1, Regs bsr 1);
+live_regs(_, _) ->
+    not_possible.
 
 x_dead([{x,N}|Rs], Regs) -> x_dead(Rs, Regs band (bnot (1 bsl N)));
 x_dead([_|Rs], Regs) -> x_dead(Rs, Regs);
diff --git a/lib/compiler/test/beam_block_SUITE.erl b/lib/compiler/test/beam_block_SUITE.erl
index 4bcb252833..9fcb6e497d 100644
--- a/lib/compiler/test/beam_block_SUITE.erl
+++ b/lib/compiler/test/beam_block_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,
-	 get_map_elements/1,otp_7345/1,move_opt_across_gc_bif/1]).
+	 get_map_elements/1,otp_7345/1,move_opt_across_gc_bif/1,
+	 erl_202/1]).
 
 %% The only test for the following functions is that
 %% the code compiles and is accepted by beam_validator.
@@ -37,7 +38,8 @@ groups() ->
     [{p,[parallel],
       [get_map_elements,
        otp_7345,
-       move_opt_across_gc_bif
+       move_opt_across_gc_bif,
+       erl_202
       ]}].
 
 init_per_suite(Config) ->
@@ -135,6 +137,27 @@ positive(speaking) ->
 
 paris([], P) -> P + 1.
 
+
+%% See https://bugs.erlang.org/browse/ERL-202.
+%% Test that move_allocates/1 in beam_block doesn't move allocate
+%% when it would not be safe.
+
+-record(erl_202_r1, {y}).
+-record(erl_202_r2, {x}).
+
+erl_202(_Config) ->
+    Ref = make_ref(),
+    Ref = erl_202({{1,2},Ref}, 42),
+
+    {Ref} = erl_202({7,8}, #erl_202_r1{y=#erl_202_r2{x=Ref}}),
+
+    ok.
+
+erl_202({{_, _},X}, _) ->
+    X;
+erl_202({_, _}, #erl_202_r1{y=R2}) ->
+    {R2#erl_202_r2.x}.
+
 %%%
 %%% The only test of the following code is that it compiles.
 %%%