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2018-03-14Teach beam_utils:replace_labels/4 to handle recv_{mark,set}Björn Gustavsson
The missing support for renumbering labels in recv_mark and recv_set did not seem to cause any problems, probably because the insructions are introduced late and their labels would keep their numbers. But it there will definitely be a problem if the recv_mark and recv_set instructions would be introduced much earlier.
2018-03-14v3_kernel: Stop ensuring one return value in #k_try{}Björn Gustavsson
For unclear reasons, v3_kernel attempts to guarantee that #k_try{} always has at least one return value, even if it will never be used. I said "attempts", because the handler block that is executed when an exception is caught does not have the same guarantee. That means that if an exception is thrown, the return value will not actually be set. In practice, however, this is not a problem for the existing code generator (v3_codegen). The generated code will still be safe. If we are to rewrite the code generator to generate an SSA-based intermediate format, this inconsistency *will* cause problems when creating phi nodes. While at it, also remove an unecessary creation of new variables in generation of #k_try_enter{}.
2018-03-14v3_kernel_pp: Print return variables for #k_try{}Björn Gustavsson
2018-03-14Merge branch 'maint'Henrik
Conflicts: OTP_VERSION
2018-03-13Merge branch 'hasse/dialyzer/extra-range/OTP-14970'Hans Bolinder
* hasse/dialyzer/extra-range/OTP-14970: ssl: Correct some specs os_mon: Correct a spec Fix broken spec in beam_asm Dialyzer should not throw away spec information because of overspec
2018-03-09Update release notesErlang/OTP
2018-03-09Update version numbersErlang/OTP
2018-03-07Merge pull request #1732 from bjorng/bjorn/compiler/beam_typeBjörn Gustavsson
Refactor and fix minor bugs in beam_type
2018-03-02Merge pull request #1731 from bjorng/bjorn/compiler/beam_utilsBjörn Gustavsson
Fix beam_utils bugs that could cause problems in the future
2018-03-02beam_type: Make sure to kill all dependencies when killing a registerBjörn Gustavsson
Make sure to kill all dependencies when a register is killed. For example, in the following code, when the type information for {x,0} is killed in the last instruction, there will still be type information for {x,1} referring to {x,0}: {get_tuple_element,{x,0},0,{x,1}}. {test,is_eq_exact,{f,5},[{x,1},{atom,tag}]}. {get_tuple_element,{x,0},1,{x,2}}. {get_tuple_element,{x,0},2,{x,0}}. This does not seems to have caused any problems in the past, but it may cause problems in the future with a register allocator that reuses register more aggressively.
2018-03-02beam_type: Refactor simplifications of instructionsBjörn Gustavsson
2018-03-02beam_type: Refactor updating of the type databaseBjörn Gustavsson
The function tdb_update/2 is problematic. It does not distinguish between assigning a register with a new value and updating information about a register that is used a as source in a test instruction. That was not a problem in practice when there were very few types, but bugs started to be noticed as more types were added. (For example, when a register was overwritten with a new value, the type for the old value stored in the same register could linger in some cases.) Introduce separate functions tdb_store/3 and tdb_meet/3 for assigning a new value to a register and for updating type information for a register referenced as as source, respectively. Also stricten verification of the types that gets stored into the type database.
2018-03-02beam_block: Fix unsafe sinking of get_tuple_element/3Björn Gustavsson
In the following code: {get_tuple_element,{x,0},0,{x,1}}. {put_tuple,2,{x,1}}. {put,{atom,badmap}}. {put,{x,0}}. {move,{x,1},{x,0}}. beam_block would move the get_tuple_element/3 instruction and eliminate the move/2 instruction: {put_tuple,2,{x,1}}. {put,{atom,badmap}}. {put,{x,0}}. {get_tuple_element,{x,0},0,{x,0}}. That is not correct, since the result of the tuple building in {x,1} is now ignored.
2018-03-01beam_utils: Correct the liveness calulcations in live_opt/1Björn Gustavsson
live_opt_block/4 could overestimate the number of live registers for a GC BIF and trigger an assertion. This does not seem to be a problem when generating code using v3_codegen, but only when using a new experimental code generator, therefore there is no need include this correction in maint.
2018-03-01beam_utils: Correct is_killed/3, is_killed_at/3, is_used/3Björn Gustavsson
is_killed/3 and is_killed_at/3 could return 'true' even if the register was referenced by an allocation instruction. Somehow, that does not seem to have caused any problems yet.
2018-03-01Enhance beam_validator to check proper nesting of try/catch and catchBjörn Gustavsson
Every catch or try/catch must use a lower Y register number than any enclosing catch or try/catch. That will ensure that when the stack is scanned when an exception occurs, the innermost try/catch tag is found first.
2018-02-21Fix broken spec in beam_asmRichard Carlsson
2018-02-14beam_block: Combine blocks when running beam_block the second timeBjörn Gustavsson
1a029efd1ad47f started to run the beam_block pass a second time, but it did not attempt to combine adjacent blocks. Combining adjacent blocks leads to many more opportunities for optimizations. After doing some diffing in generated code, it turns out that there is no benefit for beam_split to split out line instructions from blocks. It seems that the only reason it was done was to slightly simplify the implementation of the no_line_info option in beam_clean.
2018-02-14Disable CSE for floating point operationsBjörn Gustavsson
As a preparation for combining blocks before running beam_block for the second time, disable CSE for floating point operations because it will generate invalid code.
2018-02-14Merge branch 'maint'Björn Gustavsson
* maint: Check that the stack is initialized when an exception may occur
2018-02-12Fix unsafe use of 'allocate' where 'allocate_zero' should be usedBjörn Gustavsson
The more aggressive optimizations of 'allocate_zero' introduced in cb6fc15c35c7e could produce unsafe code such as the following: {allocate,0,1}. {bif,element,{f,0},[{integer,1},{x,0}],{x,0}}. The code is not safe because if element/2 fails, the runtime system may scan the stack and find garbage that looks like a catch tag, and would most probably crash. Fix the problem by making beam_utils:is_killed/3 be more conservative when asked whether a Y register will be killed. Also fix an unsafe move upwards of an allocation instruction in beam_block.
2018-02-09Check that the stack is initialized when an exception may occurBjörn Gustavsson
Strengthen beam_validator to check that the stack is initialized when an instruction with an {f,0} operand is executed. For example, the following code sequence: {allocate,0,1}. {bif,element,{f,0},[{integer,1},{x,0}],{x,0}}. should not be accepted because the stack may be scanned if element/2 fails. That could cause a crash or other undefined behavior if garbage on the stack looks like a catch tag.
2018-02-01Merge pull request #1701 from bjorng/bjorn/get_hd_tlBjörn Gustavsson
Eliminate get_list/3 internally in the compiler
2018-01-31Merge pull request #1696 from bjorng/bjorn/compiler/fix-beam_block-bug/ERL-555Björn Gustavsson
Fix incorrect handling of floating point instructions
2018-01-31Merge branch 'maint'Björn Gustavsson
* maint: Fix incorrect type interference of integer ranges Conflicts: lib/compiler/src/beam_type.erl
2018-01-30Fix incorrect handling of floating point instructionsBjörn Gustavsson
1a029efd1ad47f started to run the beam_block pass a second time. Since it is run after introduction of the optimized floating point instructions, it must handle those instructions correctly. In particular, it must be careful when hoisting allocation instructions. For example, the following code: {test_heap,{alloc,[{words,0},{floats,1}]},5}. . . . {fmove,{fr,2},{x,0}}. {allocate_zero,1,4}. must not be rewritten to: {test_heap,{alloc,[{words,0},{floats,1}]},5}. . . . {allocate_zero,1,4}. {fmove,{fr,2},{x,0}}. because beam_validator will not consider it safe. (The code may actually be safe depending on what the code between the two allocation instructions do.) https://bugs.erlang.org/browse/ERL-555
2018-01-29Fix incorrect type interference of integer rangesBjörn Gustavsson
2018-01-26Eliminate get_list/3 internally in the compilerBjörn Gustavsson
Instructions that produce more than one result complicate optimizations. get_list/3 is one of two instructions that produce multiple results (get_map_elements/3 is the other). Introduce the get_hd/2 and get_tl/2 instructions that return the head and tail of a cons cell, respectively, and use it internally in all optimization passes. For efficiency, we still want to use get_list/3 if both head and tail are used, so we will translate matching pairs of get_hd and get_tl back to get_list instructions.
2018-01-26Speed up misc_SUITE:integer_encoding/1Björn Gustavsson
misc_SUITE:integer_encoding/1 was written to make sure that big integers were encoding correctly in a reasonable amount of time. Now that beam_asm will encode big integers as literals, we can reduce the scope of integer_encode/1. That will make it significantly faster, especially when cover is running.
2018-01-26beam_asm: Encode big numbers as literalsBjörn Gustavsson
Numbers that clearly are not smalls can be encoded as literals. Conservatively, we assume that integers whose absolute value is greater than 1 bsl 128 are bignums and that they can be encoded as literals. Literals are slightly easier for the loader to handle than huge integers.
2018-01-26Merge pull request #1691 from bjorng/bjorn/compiler/local-cseBjörn Gustavsson
Do local common sub expression elimination (CSE)
2018-01-25beam_type: Optimize away unnecessary test_unit instructionsBjörn Gustavsson
Optimize away unnecessary test_unit instructions that verify that binaries are byte-aligned. In a tight loop, eliminating an instruction can have a small but measurable improvement of the execution time.
2018-01-25beam_type: Refactor simplify_basic/2 and friendsBjörn Gustavsson
Separate the simplification of instructions from updating of the type data base.
2018-01-24Optimize matching of empty binariesBjörn Gustavsson
Extend an existing optimization in beam_dead to avoid creating a match context when matching an empty binary.
2018-01-24Apply common subexpression elimination in blocksBjörn Gustavsson
Eliminate repeated evaluation of guard BIFs and building of cons cells in blocks. This optimization is applicable in more places than might be expected, because code generation for binaries and record can generate common sub expressions not visible in the original source code. For example, consider this function: make_binary(Term) -> Bin = term_to_binary(Term), Size = byte_size(Bin), <<Size:32,Bin/binary>>. The compiler inserts a call to byte_size/2 to calculate the size of the binary being built: {function, make_binary, 1, 2}. {label,1}. {line,...}. {func_info,{atom,t},{atom,make_binary},1}. {label,2}. {allocate,0,1}. {line,...}. {call_ext,1,{extfunc,erlang,term_to_binary,1}}. {line,...}. {gc_bif,byte_size,{f,0},1,[{x,0}],{x,1}}. %Present in original code. {line,...}. {gc_bif,byte_size,{f,0},2,[{x,0}],{x,2}}. %Inserted by compiler. {bs_add,{f,0},[{x,2},{integer,4},1],{x,2}}. {bs_init2,{f,0},{x,2},0,2,{field_flags,[]},{x,2}}. {bs_put_integer,{f,0},{integer,32},1,{field_flags,[unsigned,big]},{x,1}}. {bs_put_binary,{f,0},{atom,all},8,{field_flags,[unsigned,big]},{x,0}}. {move,{x,2},{x,0}}. {deallocate,0}. return. Common sub expression elimination (CSE) eliminates the second call to byte_size/2: {function, make_binary, 1, 2}. {label,1}. {line,...}. {func_info,{atom,t},{atom,make_binary},1}. {label,2}. {allocate,0,1}. {line,...}. {call_ext,1,{extfunc,erlang,term_to_binary,1}}. {line,...}. {gc_bif,byte_size,{f,0},1,[{x,0}],{x,1}}. {move,{x,1},{x,2}}. {bs_add,{f,0},[{x,2},{integer,4},1],{x,2}}. {bs_init2,{f,0},{x,2},0,2,{field_flags,[]},{x,2}}. {bs_put_integer,{f,0},{integer,32},1,{field_flags,[unsigned,big]},{x,1}}. {bs_put_binary,{f,0},{atom,all},8,{field_flags,[unsigned,big]},{x,0}}. {move,{x,2},{x,0}}. {deallocate,0}. return. Note: A possible future optimization would be to include binary construction instructions in blocks. If that is done, the {move,{x,1},{x,2}} instruction could also be eliminated.
2018-01-24Correct bug in beam_block:opt/2Björn Gustavsson
The folling sequence in a block: {move,{x,1},{x,2}}. {move,{x,2},{x,2}}. would be incorrectly rewritten to: {move,{x,2},{x,2}}. (Which in turn would be optimized away a little bit later.)
2018-01-24Correct unsafe optimizations in beam_blockBjörn Gustavsson
When attempting to eliminate the move/2 instruction in the following code: {bif,self,{f,0},[],{x,0}}. {move,{x,0},{x,1}}. . . . {put_tuple,2,{x,1}}. {put,{atom,ok}}. {put,{x,0}}. beam_block would produce the following unsafe code: {bif,self,{f,0},[],{x,1}}. . . . {put_tuple,2,{x,1}}. {put,{atom,ok}}. {put,{x,1}}. It is unsafe because the tuple is self-referential. The following code: {put_list,{y,6},nil,{x,4}}. {move,{x,4},{x,5}}. {put_list,{y,1},{x,5},{x,5}}. . . . {put_tuple,2,{x,6}}. {put,{x,4}}. {put,{x,5}}. would be incorrectly transformed to: {put_list,{y,6},nil,{x,5}}. {put_list,{y,1},{x,5},{x,5}}. . . . {put_tuple,2,{x,6}}. {put,{x,5}}. {put,{x,5}}. (Both elements in the built tuple get the same value.)
2018-01-23beam_validator: Validate building of tuplesBjörn Gustavsson
Make sure that there is the correct number of put/1 instructions following put_tuple/2. Also make it illegal to reference the register for the tuple being built in a put/1 instruction. That is, beam_validator will now issue a diagnostice for the the following code: {put_tuple,1,{x,0}}. {put,{x,0}}.
2018-01-22Don't build a stacktrace if it's only passed to erlang:raise/3Björn Gustavsson
Consider the following function: function({function,Name,Arity,CLabel,Is0}, Lc0) -> try %% Optimize the code for the function. catch Class:Error:Stack -> io:format("Function: ~w/~w\n", [Name,Arity]), erlang:raise(Class, Error, Stack) end. The stacktrace is retrieved, but it is only used in the call to erlang:raise/3. There is no need to build a stacktrace in this function. We can avoid the building if we introduce an instruction called raw_raise/3 that works exactly like the erlang:raise/3 BIF except that its third argument must be a raw stacktrace.
2018-01-16sys_core_bsm: Rearrange arguments to enable delayed sub binary creationBjörn Gustavsson
Argument order can prevent the delayed sub binary creation. Here is an example directly from the Efficiency Guide: non_opt_eq([H|T1], <<H,T2/binary>>) -> non_opt_eq(T1, T2); non_opt_eq([_|_], <<_,_/binary>>) -> false; non_opt_eq([], <<>>) -> true. When compiling with the bin_opt_info option, there will be a suggestion to change the argument order. It turns out sys_core_bsm can itself change the order, not the order of the arguments of themselves, but the order in which the arguments are matched. Here is how it can be rewritten in pseudo Core Erlang code: non_opt_eq(Arg1, Arg2) -> case < Arg2,Arg1 > of < <<H1,T2/binary>>, [H2|T1] > when H1 =:= H2 -> non_opt_eq(T1, T2); < <<_,T2/binary>ffff>, [_|T1] > -> false; < <<>>, [] >> -> true end. When rewritten like this, the bs_start_match2 instruction will be the first instruction in the function and it will be possible to store the match context in the same register as the binary ({x,1} in this case) and to delay the creation of sub binaries. The switching of matching order also enables many other simplifications in sys_core_bsm, since there is no longer any need to pass the position of the pattern as an argument. We will update the Efficiency Guide in a separate branch before the release of OTP 21.
2018-01-12beam_match_SUITE: Eliminate warnings for unused variablesBjörn Gustavsson
2018-01-12bs_match_SUITE: Add tests case written when walking into a dead endBjörn Gustavsson
Add some tests cases written when attempting some new optimizations that turned out to be unsafe.
2018-01-12Merge pull request #1680 from bjorng/bjorn/compiler/beam_blockBjörn Gustavsson
Run beam_block a second time
2018-01-12Merge pull request #1679 from bjorng/bjorn/compiler/sys_core_foldBjörn Gustavsson
Clean up and improve sys_core_fold optimizations
2018-01-11Run beam_block again after other optimizations have been runBjörn Gustavsson
Running beam_block again after the other optimizations have run will give it more opportunities for optimizations. In particular, more allocate_zero/2 instructions can be turned into allocate/2 instructions, and more get_tuple_element/3 instructions can store the retrieved value into the correct register at once. Out of a sample of about 700 modules in OTP, 64 modules were improved by this commit.
2018-01-11beam_bsm: Insert introduced 'move' instructions into blockBjörn Gustavsson
If possible, when adding move/2 instructions, try to insert them into a block. That could potentially allow them to be optimized.
2018-01-11Prepare beam_utils to run again after beam_splitBjörn Gustavsson
beam_utils:live_opt/1 is currently only run early (from beam_block). Prepare it to be run after beam_split when instructions with failure labels have been taken out of blocks. While we are it, also improve check_liveness/3. That will improve the optimizations in beam_record (replacing tuple matching instructions with an is_tagged_tuple instruction).
2018-01-11beam_utils: Correct handling of liveness for select_valBjörn Gustavsson
Since the select_val instruction never transfer directly to the next instruction, the incoming live registers should be ignored. This bug have not caused any problems yet, but it will in the future if we are to run the liveness optimizations again after the optimizations in beam_dead and beam_jump.
2018-01-11beam_block: Reorder element/2 calls in guardsBjörn Gustavsson
In a guard, reorder two consecutive calls to the element/2 BIF that access the same tuple and have the same failure label so that highest index is fetched first. That will allow the second element/2 to be replace with the slightly cheaper get_tuple_element/3 instruction.
2018-01-11Improve code generation for a 'case' with exported variablesBjörn Gustavsson
Consider a 'case' that exports variables and whose return value is ignored: foo(N) -> case N of 1 -> Res = one; 2 -> Res = two end, {ok,Res}. That code will be translated to the following Core Erlang code: 'foo'/1 = fun (_@c0) -> let <_@c5,Res> = case _@c0 of <1> when 'true' -> <'one','one'> <2> when 'true' -> <'two','two'> <_@c3> when 'true' -> primop 'match_fail'({'case_clause',_@c3}) end in {'ok',Res} The exported variables has been rewritten to explicit return values. Note that the original return value from the 'case' is bound to the variable _@c5, which is unused. The corresponding BEAM assembly code looks like this: {function, foo, 1, 2}. {label,1}. {line,[...]}. {func_info,{atom,t},{atom,foo},1}. {label,2}. {test,is_integer,{f,6},[{x,0}]}. {select_val,{x,0},{f,6},{list,[{integer,2},{f,3},{integer,1},{f,4}]}}. {label,3}. {move,{atom,two},{x,1}}. {move,{atom,two},{x,0}}. {jump,{f,5}}. {label,4}. {move,{atom,one},{x,1}}. {move,{atom,one},{x,0}}. {label,5}. {test_heap,3,2}. {put_tuple,2,{x,0}}. {put,{atom,ok}}. {put,{x,1}}. return. {label,6}. {line,[...]}. {case_end,{x,0}}. Because of the test_heap instruction following label 5, the assignment to {x,0} cannot be optimized away by the passes that optimize BEAM assembly code. Refactor the optimizations of 'let' in sys_core_fold to eliminate the unused variable. Thus: 'foo'/1 = fun (_@c0) -> let <Res> = case _@c0 of <1> when 'true' -> 'one' <2> when 'true' -> 'two' <_@c3> when 'true' -> primop 'match_fail'({'case_clause',_@c3}) end in {'ok',Res} The resulting BEAM code will look like: {function, foo, 1, 2}. {label,1}. {line,[...]}. {func_info,{atom,t},{atom,foo},1}. {label,2}. {test,is_integer,{f,6},[{x,0}]}. {select_val,{x,0},{f,6},{list,[{integer,2},{f,3},{integer,1},{f,4}]}}. {label,3}. {move,{atom,two},{x,0}}. {jump,{f,5}}. {label,4}. {move,{atom,one},{x,0}}. {label,5}. {test_heap,3,1}. {put_tuple,2,{x,1}}. {put,{atom,ok}}. {put,{x,0}}. {move,{x,1},{x,0}}. return. {label,6}. {line,[...]}. {case_end,{x,0}}.