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authorBjörn Gustavsson <[email protected]>2018-06-25 06:18:47 +0200
committerBjörn Gustavsson <[email protected]>2018-06-25 13:03:15 +0200
commit3dd17613fc7af70bc7f1222d7381533df0bd4eab (patch)
treea3064b63660a1b3ef5eebd697271898217f6e1a6 /lib/compiler/src/beam_utils.erl
parenta0ae44f324576104760a63fe6cf63e0ca31756fc (diff)
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Fix unsafe optimization when running beam_block the second time
The compiler would crash when compiling code such as: serialize(#{tag := value, id := Id, domain := Domain}) -> [case Id of nil -> error(id({required, id})); _ -> <<10, 1:16/signed, Id:16/signed>> end, case Domain of nil -> error(id({required, domain})); _ -> <<8, 2:16/signed, Domain:32/signed>> end]. The crash would look like this: Function: serialize/1 t.erl: internal error in block2; crash reason: {badmatch,false} in function beam_utils:live_opt/4 (beam_utils.erl, line 861) in call from beam_utils:live_opt/1 (beam_utils.erl, line 285) in call from beam_block:function/2 (beam_block.erl, line 47) in call from beam_block:'-module/2-lc$^0/1-0-'/2 (beam_block.erl, line 33) in call from beam_block:'-module/2-lc$^0/1-0-'/2 (beam_block.erl, line 33) in call from beam_block:module/2 (beam_block.erl, line 33) in call from compile:block2/2 (compile.erl, line 1358) in call from compile:'-internal_comp/5-anonymous-1-'/3 (compile.erl, line 349) The reason for the crash is an assertion failure caused by a previous unsafe optimization. Here is the code before the unsafe optimization: . . . {bs_init2,{f,0},7,0,0,{field_flags,[]},{x,1}}. {bs_put_string,3,{string,[8,0,2]}}. {bs_put_integer,{f,0},{integer,32},1,{field_flags,[signed,big]},{y,1}}. {move,{x,1},{x,0}}. {test_heap,4,1}. . . . beam_block:move_allocate/1 moved up the test_heap/2 instruction past the move/2 instruction, adjusting the number of live registers at the same time: . . . {bs_init2,{f,0},7,0,0,{field_flags,[]},{x,1}}. %% Only x1 is live now. {bs_put_string,3,{string,[8,0,2]}}. {bs_put_integer,{f,0},{integer,32},1,{field_flags,[signed,big]},{y,1}}. {test_heap,4,2}. %Unsafe. x0 is dead. {move,{x,1},{x,0}}. . . . This optimization is unsafe because the bs_init2 instruction killed x0. The bug is in beam_utils:anno_defs/1, which adds annotations indicating the registers that are defined at the beginning of each block. The annotation before the move/2 instruction incorrectly indicated that x0 was live. https://bugs.erlang.org/browse/ERL-650 https://github.com/elixir-lang/elixir/issues/7782
Diffstat (limited to 'lib/compiler/src/beam_utils.erl')
-rw-r--r--lib/compiler/src/beam_utils.erl8
1 files changed, 6 insertions, 2 deletions
diff --git a/lib/compiler/src/beam_utils.erl b/lib/compiler/src/beam_utils.erl
index 5510624b2d..ff587c4982 100644
--- a/lib/compiler/src/beam_utils.erl
+++ b/lib/compiler/src/beam_utils.erl
@@ -1105,8 +1105,12 @@ defs([{bif,_,{f,Fail},_Src,Dst}=I|Is], Regs0, D) ->
defs([{block,Block0}|Is], Regs0, D0) ->
{Block,Regs,D} = defs_list(Block0, Regs0, D0),
[{block,[make_anno({def,Regs0})|Block]}|defs(Is, Regs, D)];
-defs([{bs_init,{f,L},_,_,_,Dst}=I|Is], Regs0, D) ->
- Regs = def_regs([Dst], Regs0),
+defs([{bs_init,{f,L},_,Live,_,Dst}=I|Is], Regs0, D) ->
+ Regs1 = case Live of
+ none -> Regs0;
+ _ -> init_def_regs(Live)
+ end,
+ Regs = def_regs([Dst], Regs1),
[I|defs(Is, Regs, update_regs(L, Regs, D))];
defs([{bs_put,{f,L},_,_}=I|Is], Regs, D) ->
[I|defs(Is, Regs, update_regs(L, Regs, D))];