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authorBjörn Gustavsson <[email protected]>2019-01-31 13:03:28 +0100
committerBjörn Gustavsson <[email protected]>2019-01-31 15:42:06 +0100
commit53f85bfa09fa0aea9718c207d4245cb975eb6b08 (patch)
tree59c16d1ad174f2373611e3baecbf681f5aa90cc3 /lib/compiler/src/beam_except.erl
parent135f98f4481e57f82c03c74a41ebde649af40f04 (diff)
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Fix internal consistency failure caused by beam_except
Fix a bug where the number of live registers in a `bs_get_tail` instruction was too low. Consider this example: -export([bs_get_tail/2]). bs_get_tail(Bin, Config) -> bs_get_tail_1(Bin, 0, 0, Config). bs_get_tail_1(<<_:32, Rest/binary>>, Z1, Z2, F1) -> {Rest,Z1,Z2,F1}. `beam_validator` would emit the following diagnostics: t: function bs_get_tail_1/4+2: Internal consistency check failed - please report this bug. Instruction: {func_info,{atom,t},{atom,bs_get_tail_1},4} Error: {uninitialized_reg,{x,3}}: Here is the part of the code that generates the `function_clause` exception before the optimization: {test_heap,6,4}. {put_list,{x,3},nil,{x,2}}. {put_list,{integer,0},{x,2},{x,2}}. {put_list,{integer,0},{x,2},{x,2}}. {bs_set_position,{x,1},{x,0}}. {bs_get_tail,{x,1},{x,0},3}. %3 live registers. {test_heap,2,3}. {put_list,{x,0},{x,2},{x,1}}. {move,{atom,function_clause},{x,0}}. {line,[{location,"t.erl",8}]}. {call_ext_only,2,{extfunc,erlang,error,2}}. The `bs_get_tail` instruction expects that 3 registers will be live at this point. `beam_except` rewrites the code like this: {bs_set_position,{x,1},{x,0}}. {bs_get_tail,{x,1},{x,0},3}. %Still 3. Too low. {move,{integer,0},{x,1}}. {move,{integer,0},{x,2}}. {jump,{f,3}}. Now the number of live registers in `bs_get_tail` is too low, because the `{x,3}` register will become undefined. This commit adds code to update the number of live registers in the `bs_get_tail` instruction, producing this code: {bs_set_position,{x,1},{x,0}}. {bs_get_tail,{x,1},{x,0},4}. %Adjusted to 4. {move,{integer,0},{x,1}}. {move,{integer,0},{x,2}}. {jump,{f,3}}.
Diffstat (limited to 'lib/compiler/src/beam_except.erl')
-rw-r--r--lib/compiler/src/beam_except.erl23
1 files changed, 21 insertions, 2 deletions
diff --git a/lib/compiler/src/beam_except.erl b/lib/compiler/src/beam_except.erl
index 254a716b81..09925b2872 100644
--- a/lib/compiler/src/beam_except.erl
+++ b/lib/compiler/src/beam_except.erl
@@ -167,8 +167,10 @@ dig_out_fc_1([{block,Bl}|Is], Regs0, Acc) ->
dig_out_fc_1(Is, Regs, Acc);
dig_out_fc_1([{bs_set_position,_,_}=I|Is], Regs, Acc) ->
dig_out_fc_1(Is, Regs, [I|Acc]);
-dig_out_fc_1([{bs_get_tail,_,_,Live}=I|Is], Regs0, Acc) ->
- Regs = prune_xregs(Live, Regs0),
+dig_out_fc_1([{bs_get_tail,Src,Dst,Live0}|Is], Regs0, Acc) ->
+ Regs = prune_xregs(Live0, Regs0),
+ Live = dig_out_stack_live(Regs, Live0),
+ I = {bs_get_tail,Src,Dst,Live},
dig_out_fc_1(Is, Regs, [I|Acc]);
dig_out_fc_1([_|_], _Regs, _Acc) ->
{#{},[]};
@@ -189,6 +191,23 @@ dig_out_fc_block([{set,_,_,_}|_], _Regs) ->
#{};
dig_out_fc_block([], Regs) -> Regs.
+dig_out_stack_live(Regs, Default) ->
+ Reg = {x,2},
+ case Regs of
+ #{Reg:=List} ->
+ dig_out_stack_live_1(List, Default);
+ #{} ->
+ Default
+ end.
+
+dig_out_stack_live_1({cons,{arg,N},T}, Live) ->
+ dig_out_stack_live_1(T, max(N + 1, Live));
+dig_out_stack_live_1({cons,_,T}, Live) ->
+ dig_out_stack_live_1(T, Live);
+dig_out_stack_live_1(nil, Live) ->
+ Live;
+dig_out_stack_live_1(_, Live) -> Live.
+
prune_xregs(Live, Regs) ->
maps:filter(fun({x,X}, _) -> X < Live end, Regs).