otp.git - Mirror of Erlang/OTP repository.

Age	Commit message (Collapse)	Author
2018-09-26	Move peephole optimization from beam_block to beam_a	Björn Gustavsson
	Moving away this optimization makes beam_block do one thing and one thing only -- creating blocks.
2018-09-12	Move two optimizations from beam_dead to beam_a	Björn Gustavsson
	The 'move' instruction can be eliminated in code such as: {test,is_eq_exact,{f,42},[{x,0},{atom,value}]}. {move,{atom,value},{x,0}}. Move that optimization from beam_dead to beam_a. The optimization will be simpler because the 'move' instruction has not yet been moved into a block. Getting rid of 'move' earlier will also save work for later passes. Also move the optimization that eliminates instructions such as from beam_dead to beam_a: {test_is_eq_exact,{f,42},[{x,0},{x,0}]}.
2018-08-24	Introduce a new SSA-based intermediate format	Björn Gustavsson
	v3_codegen is replaced by three new passes: * beam_kernel_to_ssa which translates the Kernel Erlang format to a new SSA-based intermediate format. * beam_ssa_pre_codegen which prepares the SSA-based format for code generation, including register allocation. Registers are allocated using the linear scan algorithm. * beam_ssa_codegen which generates BEAM assembly code from the SSA-based format. It easier and more effective to optimize the SSA-based format before X and Y registers have been assigned. The current optimization passes constantly have to make sure no "holes" in the X register assignments are created (that is, that no X register becomes undefined that an allocation instruction depends on). This commit also introduces the following optimizations: * Replacing of tuple matching of records with the is_tagged_tuple instruction. (Replacing beam_record.) * Sinking of get_tuple_element instructions to just before the first use of the extracted values. As well as potentially avoiding extracting tuple elements when they are not actually used on all executions paths, this optimization could also reduce the number values that will need to be stored in Y registers. (Similar to beam_reorder, but more effective.) * Live optimizations, removing the definition of a variable that is not subsequently used (provided that the operation has no side effects), as well strength reduction of binary matching by replacing the extraction of value from a binary with a skip instruction. (Used to be done by beam_block, beam_utils, and v3_codegen.) * Removal of redundant bs_restore2 instructions. (Formerly done by beam_bs.) * Type-based optimizations across branches. More effective than the old beam_type pass that only did type-based optimizations in basic blocks. * Optimization of floating point instructions. (Formerly done by beam_type.) * Optimization of receive statements to introduce recv_mark and recv_set instructions. More effective with far fewer restrictions on what instructions are allowed between creating the reference and entering the receive statement. * Common subexpression elimination. (Formerly done by beam_block.)
2018-08-17	Simplify optimizations by introducing is_nil late	Björn Gustavsson

2018-06-18	Update copyright year	Henrik Nord

2018-01-26	Eliminate get_list/3 internally in the compiler	Björn 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.
2018-01-11	Refactor '%live' and '%def' annotations	Björn Gustavsson
	The annotations in the optimizing passes currently looks like this: {'%live',NumRegistersUsed,RegistersUsedBitmap} {'%def',RegistersDefinedBitmap} (NumRegistersUsed is no longer used.) When I attempted to extend some optimizations, I found that I had to add additional clauses to tolerate/handle both types of annotations. That problem would only get worse if any more annotations are added in the future. To simplify annotation handling, this commit wraps both types of annotations in a {'%anno',_} tuple: {'%anno',{used,RegistersUsedBitmap}} {'%anno',{def,RegistersDefinedBitmap}} The '%live' annotation has been renamed to 'used' to make it somewhat clearer what it means, and the unused NumRegistersUsed part of the old annotation has been removed. Alternatives considered: My first attempt was to wrap the annotation in a 'set' tuple so that there would only be 'set' tuples in a block. For example: {set,[],[],{anno,{live,RegistersUsedBitmap}}} It was not as convenient as expected. Annotations often need to be handled specially from other instructions in a block. When they are wrapped in a 'set' tuple, they can very easily be handled incorrectly or passed on to the next pass. That causes subtle errors or worse code, and it can be difficult to debug. Therefore, my conclusion is that annotations should be distinct from other instructions, to make it obvious when one have missed to handle an annotation.
2017-12-08	Use the new syntax for retrieving stack traces	Björn Gustavsson

2017-01-12	Add specs for the beam_*:module/2 functions	Björn Gustavsson

2016-03-15	update copyright-year	Henrik Nord

2015-06-18	Change license text to APLv2	Bruce Yinhe

2015-04-22	Move rewriting of bs_match from beam_clean to beam_z	Björn Gustavsson
	The actual bs_match_string instruction has four operands: bs_match_string {f,Lbl} Ctxt NumBits {string,ListOfBytes} However, v3_codegen emits a more compact representation where the bits to match are packaged in a bitstring: bs_match_string {f,Lbl} Ctxt Bitstring Currently, beam_clean:clean_labels/1 will rewrite the compact representation to the final representation. That is unfortunate since clean_labels/1 is called by beam_dead, which means that the less compact representation will be introduced long before it is actually needed by beam_asm. It will also complicate any optimizations that we might want to do. Move the rewriting of bs_match_string from beam_clean:clean_labels/1 to the beam_z pass, which is the last pass executed before beam_validator and beam_asm.
2015-03-09	Introduce '%live' annotations with a complete register map	Björn Gustavsson
	As a preparation for fixing a bug, introduce a complete register map in the '%live' annotations.
2014-02-13	compiler: Change map instructions for fetching values	Björn-Egil Dahlberg
	* Combine multiple get values with one instruction * Combine multiple check keys with one instruction
2014-01-28	compiler: Implement different instructions for => and :=	Björn Gustavsson

2013-06-12	Update copyright years	Björn-Egil Dahlberg

2013-05-28	Fix renaming of bs_put_string instructions	Anthony Ramine
	The clause was formerly commented-out because at this point in the code, no bs_put_string instruction has been generated yet when compiling from Erlang. If an Erlang module is compiled to BEAM assembly and the result contains a bs_put_string instruction, the output can't be compiled to binary anymore and the compiler crashes with the following error: $ erlc prs.S Function: compress/1 prs.S:none: internal error in beam_block; crash reason: {{case_clause, {'EXIT', {function_clause, [{beam_utils,live_opt, [[{bs_put_string,1,{string,[0]}}, {bs_init, {f,0}, {bs_append,0,8,{field_flags,[]}}, 0, [{integer,8},{x,0}], {x,1}}, {label,2}], 2, {1,{1,1,nil,nil}}, [{block, [{'%live',2}, {set,[{x,0}],[{x,1}],move}, {'%live',1}]}, return]], [{file,"beam_utils.erl"},{line,639}]}, {beam_utils,live_opt,1, [{file,"beam_utils.erl"},{line,205}]}, {beam_block,function,2, [{file,"beam_block.erl"},{line,38}]}, {lists,mapfoldl,3, [{file,"lists.erl"},{line,1329}]}, {beam_block,module,2, [{file,"beam_block.erl"},{line,29}]}, {compile,'-select_passes/2-anonymous-2-',2, [{file,"compile.erl"},{line,476}]}, {compile,'-internal_comp/4-anonymous-1-',2, [{file,"compile.erl"},{line,276}]}, {compile,fold_comp,3, [{file,"compile.erl"},{line,294}]}]}}}, [{compile,'-select_passes/2-anonymous-2-',2, [{file,"compile.erl"},{line,476}]}, {compile,'-internal_comp/4-anonymous-1-',2, [{file,"compile.erl"},{line,276}]}, {compile,fold_comp,3,[{file,"compile.erl"},{line,294}]}, {compile,internal_comp,4,[{file,"compile.erl"},{line,278}]}, {compile,'-do_compile/2-anonymous-0-',2, [{file,"compile.erl"},{line,152}]}]}
2012-10-10	Break apart tail-recursive call instructions	Björn Gustavsson
	Somewhat reduce the code bloat by eliminating special cases.
2012-10-10	Represent the 'send' instruction as a call_ext/2 instruction	Björn Gustavsson
	Somewhat reduce code bloat.
2012-10-10	Rewrite select_val and select_tuple_arity to a select instruction	Björn Gustavsson
	Eliminate some code bloat.
2012-10-09	Rewrite binary creation instructions to bs_init instructions	Björn Gustavsson
	Rewrite the five binary creation instructions to a bs_init instruction, in order to somewhat reduce code bloat.
2012-10-09	Rewrite bs_add, bs_utf*_size to BIF instructions in optimizations	Björn 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).
2012-10-09	Rewrite bs_put* instructions to a generic bs_put instruction	Björn 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.
2012-10-09	Refactor removal of unused labels	Björn Gustavsson
	Since we always want to remove unused labels directly after code generation (whether we'll run the optimization passes or not), we can simplify the code by doing it in beam_a.
2012-10-09	Introduce the mandatory beam_a and beam_z passes	Björn Gustavsson
	Introduce the mandary beam_a pass that will be run directly after code generation, and the mandatory beam_z pass that will be run just before beam_asm. Since these passes surround the optimizations, beam_a can (for example) do instruction renaming to simplify the optimization passes and beam_z can undo those renamings.