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2016-10-06beam_bsm: Eliminate unsafe optimizationBjörn Gustavsson
The following code causes a compiler failure: first_after(Data, Offset) -> case byte_size(Data) > Offset of false -> {First, Rest} = {ok, ok}, ok; true -> <<_:Offset/binary, Rest/binary>> = Data, %% 'Rest' saved in y(0) before the call. {First, _} = match_first(Data, Rest), %% When beam_bsm sees the code, the following line %% which uses y(0) has been optimized away. {First, Rest} = {First, Rest}, First end. match_first(_, <<First:1/binary, Rest/binary>>) -> {First, Rest}. Here is the error message from beam_validator: t: function first_after/2+15: Internal consistency check failed - please report this bug. Instruction: {call,2,{f,7}} Error: {multiple_match_contexts,[{x,1},0]}: Basically, what happens is that at time of code generation, the variable 'Rest' is needed after the call to match_first/2 and is therefore saved in y(0). When beam_bsm (a late optimization pass) sees the code, the use of y(0) following the call to match_first/2 has been optimized away. beam_bsm therefore assumes that the delayed sub-binary creation is safe. (Actually, it is safe, but beam_validator does not realize it.) The bug was caused by two separate commits: e199e2471a reduced the number of special cases to handle in BEAM optimization passed by breaking apart the tail-recursive call instructions (call_only and call_last) into separate instructions. Unfortunately, the special handling for tail calls was lost, which resulted in worse code (i.e. the delayed sub-binary creation optimization could not be applied). e1aa422290 tried to compensate, but did so in a way that was not always safe. Teaching beam_validator that this kind of code is safe would be expensive. Instead, we will undo the damage caused by the two commits. Re-introduce the special handling of tail-recursive calls in beam_bsm that was lost in the first commit. (Effectively) revert the change in the second commit. ERL-268
2016-03-15update copyright-yearHenrik Nord
2016-02-08Eliminate crash because of unsafe delaying of sub-binary creationBjörn Gustavsson
The following code would fail to compile: decode(<<Code/integer, Bin/binary>>) -> <<C1/integer, B1/binary>> = Bin, case C1 of X when X =:= 1 orelse X =:= 2 -> Bin2 = <<>>; _ -> Bin2 = B1 end, case Code of 1 -> decode(Bin2); _ -> Bin2 end. The error message would be: t: function decode/1+28: Internal consistency check failed - please report this bug. Instruction: return Error: {match_context,{x,0}}: The beam_bsm pass would delay the creation of a sub-binary when it was unsafe to do so. The culprit was the btb_follow_branch/3 function that for performance reasons cached labels that had already been checked. The problem was the safety of a label also depends on the contents of the registers. Therefore, the key for caching needs to be both the label and the register contents. Reported-by: José Valim
2015-06-18Change license text to APLv2Bruce Yinhe
2015-05-21compiler: Teach beam_bsm get_map_elements instructionBjörn-Egil Dahlberg
Allows for 'creation of sub binary delayed' optimization if map instructions are in a clause. Reported-by: José Valim
2015-04-30compiler: Use module erl_annoHans Bolinder
2015-04-22beam_bsm: Optimize btb_index()Björn Gustavsson
lists:dropwhile/2 and the fun in btb_index_1/2 shows up in the top 10 list of eprof. Replace dropwhile with a special-purpose function for a tiny increase in speed.
2014-02-05beam_bsm: Eliminate emulator crash when a binary is calledBjörn Gustavsson
We must not do the delayed binary creation optimization if the code attempts to call the matched out binary. Calling a matchstate will crash the run-time system. Reported-by: Loïc Hoguin
2013-01-25Update copyright yearsBjörn-Egil Dahlberg
2012-11-26beam_bsm: Improve handling of bs_start_match2 instructionsBjörn Gustavsson
The handling of bs_start_match2 was both too conservative and too careless. It was too conservative in that would not do the optimization if the were copies of the match state in other registers. It was careless in that it did not consider the failure branch. Reorganize the code and fix both these issues. Add a test case to test that the failure branch is considered.
2012-11-26beam_bsm: Make the optimization applicable in more circumstancesBjörn Gustavsson
When determining whether the delayed creation of sub-binaries optimizations is applicable, this module some tests whether the register containg the match state is killed. That is actually a stronger condition than necessary; since the register is initialized, it suffices to test whether the register is unused.
2012-10-10beam_bsm: Handle calls slightly betterBjörn Gustavsson
We were too conservative when handling a call when there were copies of the match context in both x and y registers. Don't give up if there is are copies of the match context in y registers, as long as those copies are killed by the code that follows the call.
2012-10-10Break apart tail-recursive call instructionsBjörn Gustavsson
Somewhat reduce the code bloat by eliminating special cases.
2012-10-10Represent the 'send' instruction as a call_ext/2 instructionBjörn Gustavsson
Somewhat reduce code bloat.
2012-10-10Rewrite select_val and select_tuple_arity to a select instructionBjörn Gustavsson
Eliminate some code bloat.
2012-10-09Rewrite binary creation instructions to bs_init instructionsBjörn Gustavsson
Rewrite the five binary creation instructions to a bs_init instruction, in order to somewhat reduce code bloat.
2012-10-09Rewrite bs_add, bs_utf*_size to BIF instructions in optimizationsBjörn Gustavsson
We can remove some code bloat by handling the special instructions as BIF instructions in the optimization passes. Also note that bs_utf*_size was not handled by beam_utils:check_liveness/3 (meaning the conservative answer instead of the correct answer would be returned).
2012-10-09Rewrite bs_put* instructions to a generic bs_put instructionBjörn Gustavsson
Seven bs_put_* instructions can be combined into one generic bs_put instruction to avoid some code bloat. That will also improve some optimizations (such as beam_trim) that did not handle all bs_put* variants.
2011-08-16compiler: Generate line instructionsBjörn Gustavsson
2011-05-20Update copyright yearsBjörn-Egil Dahlberg
2011-04-12beam_bsm: Eliminate uncovered line in warning generationBjörn Gustavsson
In warning_translate_label/2, gb_trees:lookup/2 is called to translate from the entry label for a function to its name. Since the gb_tree has an entry for all functions in the module, there is no way that the lookup can fail unless there is a serious bug. Therefore, use gb_trees:get/2 so that an exception and an internal compiler error will be generated if the lookup would ever fail.
2009-11-20The R13B03 release.OTP_R13B03Erlang/OTP