CHANGELOG

List of major changes and improvements between releases
=======================================================


Yosys 0.9 .. Yosys 0.9-dev
--------------------------

 * Various
    - Added "write_xaiger" backend
    - Added "abc9" pass for timing-aware techmapping (experimental, FPGA only)
    - Added "synth_xilinx -abc9" (experimental)
    - Added "synth_ice40 -abc9" (experimental)
    - Added "synth -abc9" (experimental)
    - Added "script -scriptwire"
    - Added "synth_xilinx -nocarry"
    - Added "synth_xilinx -nowidelut"
    - Added "synth_ecp5 -nowidelut"
    - "synth_xilinx" to now infer wide multiplexers (-widemux <min> to enable)
    - Renamed labels/options in synth_ice40 (e.g. dram -> map_lutram; -nodram -> -nolutram)
    - Renamed labels/options in synth_ecp5 (e.g. dram -> map_lutram; -nodram -> -nolutram)
    - Renamed labels in synth_intel (e.g. bram -> map_bram)
    - Renamed labels/options in synth_xilinx (e.g. dram -> map_lutram; -nodram -> -nolutram)
    - Added automatic gzip decompression for frontends
    - Added $_NMUX_ cell type
    - Added automatic gzip compression (based on filename extension) for backends
    - Improve attribute and parameter encoding in JSON to avoid ambiguities between
      bit vectors and strings containing [01xz]*
    - Added "clkbufmap" pass
    - Added "extractinv" pass and "invertible_pin" attribute
    - Added "synth_xilinx -family xc6s" for Spartan 6 support (experimental)
    - Added "synth_xilinx -ise" (experimental)
    - Added "synth_xilinx -iopad"
    - "synth_xilinx" now automatically inserts clock buffers (add -noclkbuf to disable)
    - Improvements in pmgen: subpattern and recursive matches
    - Added "opt_share" pass, run as part of "opt -full"
    - Added "ice40_wrapcarry" to encapsulate SB_LUT+SB_CARRY pairs for techmapping
    - Removed "ice40_unlut"
    - Improvements in pmgen: slices, choices, define, generate
    - Added "xilinx_srl" for Xilinx shift register extraction
    - Removed "shregmap -tech xilinx" (superseded by "xilinx_srl")
    - Added "_TECHMAP_WIREINIT_*_" attribute and "_TECHMAP_REMOVEINIT_*_" wire for "techmap" pass
    - Added "-match-init" option to "dff2dffs" pass
    - Added "techmap_autopurge" support to techmap
    - Added "add -mod <modname[s]>"
    - Added +/mul2dsp.v for decomposing wide multipliers to custom-sized ones
    - Added "ice40_dsp" for Lattice iCE40 DSP packing
    - Added "xilinx_dsp" for Xilinx DSP packing
    - "synth_xilinx" to now infer DSP blocks (-nodsp to disable)
    - "synth_ecp5" to now infer DSP blocks (-nodsp to disable, experimental)
    - "synth_ice40 -dsp" to infer DSP blocks
    - Added latch support to synth_xilinx
    - Added support for flip-flops with synchronous reset to synth_xilinx
    - Added support for flip-flops with reset and enable to synth_xilinx
    - Added "check -mapped"
    - Added checking of SystemVerilog always block types (always_comb,
      always_latch and always_ff)
    - Added support for SystemVerilog wildcard port connections (.*)
    - Added "xilinx_dffopt" pass
    - Added "scratchpad" pass
    - Added "synth_xilinx -dff"
    - Improved support of $readmem[hb] Memory Content File inclusion
    - Added "opt_lut_ins" pass
    - Added "logger" pass
    - Removed "dffsr2dff" (use opt_rmdff instead)
    - Added "design -delete"
    - Added "select -unset"
    - Use YosysHQ/abc instead of upstream berkeley-abc/abc

Yosys 0.8 .. Yosys 0.9
----------------------

 * Various
    - Many bugfixes and small improvements
    - Added support for SystemVerilog interfaces and modports
    - Added "write_edif -attrprop"
    - Added "opt_lut" pass
    - Added "gate2lut.v" techmap rule
    - Added "rename -src"
    - Added "equiv_opt" pass
    - Added "flowmap" LUT mapping pass
    - Added "rename -wire" to rename cells based on the wires they drive
    - Added "bugpoint" for creating minimised testcases
    - Added "write_edif -gndvccy"
    - "write_verilog" to escape Verilog keywords
    - Fixed sign handling of real constants
    - "write_verilog" to write initial statement for initial flop state
    - Added pmgen pattern matcher generator
    - Fixed opt_rmdff handling of $_DFFSR_???_ and $_DLATCHSR_???_
    - Added "setundef -params" to replace undefined cell parameters
    - Renamed "yosys -D" to "yosys -U", added "yosys -D" to set Verilog defines
    - Fixed handling of defparam when default_nettype is none
    - Fixed "wreduce" flipflop handling
    - Fixed FIRRTL to Verilog process instance subfield assignment
    - Added "write_verilog -siminit"
    - Several fixes and improvements for mem2reg memories
    - Fixed handling of task output ports in clocked always blocks
    - Improved handling of and-with-1 and or-with-0 in "opt_expr"
    - Added "read_aiger" frontend
    - Added "mutate" pass
    - Added "hdlname" attribute
    - Added "rename -output"
    - Added "read_ilang -lib"
    - Improved "proc" full_case detection and handling
    - Added "whitebox" and "lib_whitebox" attributes
    - Added "read_verilog -nowb", "flatten -wb" and "wbflip"
    - Added Python bindings and support for Python plug-ins
    - Added "pmux2shiftx"
    - Added log_debug framework for reduced default verbosity
    - Improved "opt_expr" and "opt_clean" handling of (partially) undriven and/or unused wires
    - Added "peepopt" peephole optimisation pass using pmgen
    - Added approximate support for SystemVerilog "var" keyword
    - Added parsing of "specify" blocks into $specrule and $specify[23]
    - Added support for attributes on parameters and localparams
    - Added support for parsing attributes on port connections
    - Added "wreduce -keepdc"
    - Added support for optimising $dffe and $_DFFE_* cells in "opt_rmdff"
    - Added Verilog wand/wor wire type support
    - Added support for elaboration system tasks
    - Added "muxcover -mux{4,8,16}=<cost>"
    - Added "muxcover -dmux=<cost>"
    - Added "muxcover -nopartial"
    - Added "muxpack" pass
    - Added "pmux2shiftx -norange"
    - Added support for "~" in filename parsing
    - Added "read_verilog -pwires" feature to turn parameters into wires
    - Fixed sign extension of unsized constants with 'bx and 'bz MSB
    - Fixed genvar to be a signed type
    - Added support for attributes on case rules
    - Added "upto" and "offset" to JSON frontend and backend
    - Several liberty file parser improvements
    - Fixed handling of more complex BRAM patterns
    - Add "write_aiger -I -O -B"

 * Formal Verification
    - Added $changed support to read_verilog
    - Added "read_verilog -noassert -noassume -assert-assumes"
    - Added btor ops for $mul, $div, $mod and $concat
    - Added yosys-smtbmc support for btor witnesses
    - Added "supercover" pass
    - Fixed $global_clock handling vs autowire
    - Added $dffsr support to "async2sync"
    - Added "fmcombine" pass
    - Added memory init support in "write_btor"
    - Added "cutpoint" pass
    - Changed "ne" to "neq" in btor2 output
    - Added support for SVA "final" keyword
    - Added "fmcombine -initeq -anyeq"
    - Added timescale and generated-by header to yosys-smtbmc vcd output
    - Improved BTOR2 handling of undriven wires

 * Verific support
    - Enabled Verific flags vhdl_support_variable_slice and veri_elaborate_top_level_modules_having_interface_ports
    - Improved support for asymmetric memories
    - Added "verific -chparam"
    - Fixed "verific -extnets" for more complex situations
    - Added "read -verific" and "read -noverific"
    - Added "hierarchy -chparam"

 * New back-ends
    - Added initial Anlogic support
    - Added initial SmartFusion2 and IGLOO2 support

 * ECP5 support
    - Added "synth_ecp5 -nowidelut"
    - Added BRAM inference support to "synth_ecp5"
    - Added support for transforming Diamond IO and flipflop primitives

 * iCE40 support
    - Added "ice40_unlut" pass
    - Added "synth_ice40 -relut"
    - Added "synth_ice40 -noabc"
    - Added "synth_ice40 -dffe_min_ce_use"
    - Added DSP inference support using pmgen
    - Added support for initialising BRAM primitives from a file
    - Added iCE40 Ultra RGB LED driver cells

 * Xilinx support
    - Use "write_edif -pvector bra" for Xilinx EDIF files
    - Fixes for VPR place and route support with "synth_xilinx"
    - Added more cell simulation models
    - Added "synth_xilinx -family"
    - Added "stat -tech xilinx" to estimate logic cell usage
    - Added "synth_xilinx -nocarry"
    - Added "synth_xilinx -nowidelut"
    - "synth_xilinx" to now infer hard shift registers (-nosrl to disable)
    - Added support for mapping RAM32X1D

Yosys 0.7 .. Yosys 0.8
----------------------

 * Various
    - Many bugfixes and small improvements
    - Strip debug symbols from installed binary
    - Replace -ignore_redef with -[no]overwrite in front-ends
    - Added write_verilog hex dump support, add -nohex option
    - Added "write_verilog -decimal"
    - Added "scc -set_attr"
    - Added "verilog_defines" command
    - Remember defines from one read_verilog to next
    - Added support for hierarchical defparam
    - Added FIRRTL back-end
    - Improved ABC default scripts
    - Added "design -reset-vlog"
    - Added "yosys -W regex", "yosys -w regex", and "yosys -e regex"
    - Added Verilog $rtoi and $itor support
    - Added "check -initdrv"
    - Added "read_blif -wideports"
    - Added support for SystemVerilog "++" and "--" operators
    - Added support for SystemVerilog unique, unique0, and priority case
    - Added "write_edif" options for edif "flavors"
    - Added support for resetall compiler directive
    - Added simple C beck-end (bitwise combinatorical only atm)
    - Added $_ANDNOT_ and $_ORNOT_ cell types
    - Added cell library aliases to "abc -g"
    - Added "setundef -anyseq"
    - Added "chtype" command
    - Added "design -import"
    - Added "write_table" command
    - Added "read_json" command
    - Added "sim" command
    - Added "extract_fa" and "extract_reduce" commands
    - Added "extract_counter" command
    - Added "opt_demorgan" command
    - Added support for $size and $bits SystemVerilog functions
    - Added "blackbox" command
    - Added "ltp" command
    - Added support for editline as replacement for readline
    - Added warnings for driver-driver conflicts between FFs (and other cells) and constants
    - Added "yosys -E" for creating Makefile dependencies files
    - Added "synth -noshare"
    - Added "memory_nordff"
    - Added "setundef -undef -expose -anyconst"
    - Added "expose -input"
    - Added specify/specparam parser support (simply ignore them)
    - Added "write_blif -inames -iattr"
    - Added "hierarchy -simcheck"
    - Added an option to statically link abc into yosys
    - Added protobuf back-end
    - Added BLIF parsing support for .conn and .cname
    - Added read_verilog error checking for reg/wire/logic misuse
    - Added "make coverage" and ENABLE_GCOV build option

 * Changes in Yosys APIs
    - Added ConstEval defaultval feature
    - Added {get,set}_src_attribute() methods on RTLIL::AttrObject
    - Added SigSpec::is_fully_ones() and Const::is_fully_ones()
    - Added log_file_warning() and log_file_error() functions

 * Formal Verification
    - Added "write_aiger"
    - Added "yosys-smtbmc --aig"
    - Added "always <positive_int>" to .smtc format
    - Added $cover cell type and support for cover properties
    - Added $fair/$live cell type and support for liveness properties
    - Added smtbmc support for memory vcd dumping
    - Added "chformal" command
    - Added "write_smt2 -stbv" and "write_smt2 -stdt"
    - Fix equiv_simple, old behavior now available with "equiv_simple -short"
    - Change to Yices2 as default SMT solver (it is GPL now)
    - Added "yosys-smtbmc --presat" (now default in SymbiYosys)
    - Added "yosys-smtbmc --smtc-init --smtc-top --noinit"
    - Added a brand new "write_btor" command for BTOR2
    - Added clk2fflogic memory support and other improvements
    - Added "async memory write" support to write_smt2
    - Simulate clock toggling in yosys-smtbmc VCD output
    - Added $allseq/$allconst cells for EA-solving
    - Make -nordff the default in "prep"
    - Added (* gclk *) attribute
    - Added "async2sync" pass for single-clock designs with async resets

 * Verific support
    - Many improvements in Verific front-end
    - Added proper handling of concurent SVA properties
    - Map "const" and "rand const" to $anyseq/$anyconst
    - Added "verific -import -flatten" and "verific -import -extnets"
    - Added "verific -vlog-incdir -vlog-define -vlog-libdir"
    - Remove PSL support (because PSL has been removed in upstream Verific)
    - Improve integration with "hierarchy" command design elaboration
    - Added YOSYS_NOVERIFIC for running non-verific test cases with verific bin
    - Added simpilied "read" command that automatically uses verific if available
    - Added "verific -set-<severity> <msg_id>.."
    - Added "verific -work <libname>"

 * New back-ends
    - Added initial Coolrunner-II support
    - Added initial eASIC support
    - Added initial ECP5 support

 * GreenPAK Support
    - Added support for GP_DLATCH, GP_SPI, GP_DCMx, GP_COUNTx, etc.

 * iCE40 Support
    - Add "synth_ice40 -vpr"
    - Add "synth_ice40 -nodffe"
    - Add "synth_ice40 -json"
    - Add Support for UltraPlus cells

 * MAX10 and Cyclone IV Support
    - Added initial version of metacommand "synth_intel".
    - Improved write_verilog command to produce VQM netlist for Quartus Prime.
    - Added support for MAX10 FPGA family synthesis.
    - Added support for Cyclone IV family synthesis.
    - Added example of implementation for DE2i-150 board.
    - Added example of implementation for MAX10 development kit.
    - Added LFSR example from Asic World.
    - Added "dffinit -highlow" for mapping to Intel primitives


Yosys 0.6 .. Yosys 0.7
----------------------

 * Various
    - Added "yosys -D" feature
    - Added support for installed plugins in $(DATDIR)/plugins/
    - Renamed opt_const to opt_expr
    - Renamed opt_share to opt_merge
    - Added "prep -flatten" and "synth -flatten"
    - Added "prep -auto-top" and "synth -auto-top"
    - Using "mfs" and "lutpack" in ABC lut mapping
    - Support for abstract modules in chparam
    - Cleanup abstract modules at end of "hierarchy -top"
    - Added tristate buffer support to iopadmap
    - Added opt_expr support for div/mod by power-of-two
    - Added "select -assert-min <N> -assert-max <N>"
    - Added "attrmvcp" pass
    - Added "attrmap" command
    - Added "tee +INT -INT"
    - Added "zinit" pass
    - Added "setparam -type"
    - Added "shregmap" pass
    - Added "setundef -init"
    - Added "nlutmap -assert"
    - Added $sop cell type and "abc -sop -I <num> -P <num>"
    - Added "dc2" to default ABC scripts
    - Added "deminout"
    - Added "insbuf" command
    - Added "prep -nomem"
    - Added "opt_rmdff -keepdc"
    - Added "prep -nokeepdc"
    - Added initial version of "synth_gowin"
    - Added "fsm_expand -full"
    - Added support for fsm_encoding="user"
    - Many improvements in GreenPAK4 support
    - Added black box modules for all Xilinx 7-series lib cells
    - Added synth_ice40 support for latches via logic loops
    - Fixed ice40_opt lut unmapping, added "ice40_opt -unlut"

 * Build System
    - Added ABCEXTERNAL and ABCURL make variables
    - Added BINDIR, LIBDIR, and DATDIR make variables
    - Added PKG_CONFIG make variable
    - Added SEED make variable (for "make test")
    - Added YOSYS_VER_STR make variable
    - Updated min GCC requirement to GCC 4.8
    - Updated required Bison version to Bison 3.x

 * Internal APIs
    - Added ast.h to exported headers
    - Added ScriptPass helper class for script-like passes
    - Added CellEdgesDatabase API

 * Front-ends and Back-ends
    - Added filename glob support to all front-ends
    - Added avail (black-box) module params to ilang format
    - Added $display %m support
    - Added support for $stop Verilog system task
    - Added support for SystemVerilog packages
    - Fixed procedural assignments to non-unique lvalues, e.g. {y,y} = {a,b}
    - Added support for "active high" and "active low" latches in read_blif and write_blif
    - Use init value "2" for all uninitialized FFs in BLIF back-end
    - Added "read_blif -sop"
    - Added "write_blif -noalias"
    - Added various write_blif options for VTR support
    - write_json: also write module attributes.
    - Added "write_verilog -nodec -nostr -defparam"
    - Added "read_verilog -norestrict -assume-asserts"
    - Added support for bus interfaces to "read_liberty -lib"
    - Added liberty parser support for types within cell decls
    - Added "write_verilog -renameprefix -v"
    - Added "write_edif -nogndvcc"

 * Formal Verification
    - Support for hierarchical designs in smt2 back-end
    - Yosys-smtbmc: Support for hierarchical VCD dumping
    - Added $initstate cell type and vlog function
    - Added $anyconst and $anyseq cell types and vlog functions
    - Added printing of code loc of failed asserts to yosys-smtbmc
    - Added memory_memx pass, "memory -memx", and "prep -memx"
    - Added "proc_mux -ifx"
    - Added "yosys-smtbmc -g"
    - Deprecated "write_smt2 -regs" (by default on now)
    - Made "write_smt2 -bv -mem" default, added "write_smt2 -nobv -nomem"
    - Added support for memories to smtio.py
    - Added "yosys-smtbmc --dump-vlogtb"
    - Added "yosys-smtbmc --smtc --dump-smtc"
    - Added "yosys-smtbmc --dump-all"
    - Added assertpmux command
    - Added "yosys-smtbmc --unroll"
    - Added $past, $stable, $rose, $fell SVA functions
    - Added "yosys-smtbmc --noinfo and --dummy"
    - Added "yosys-smtbmc --noincr"
    - Added "yosys-smtbmc --cex <filename>"
    - Added $ff and $_FF_ cell types
    - Added $global_clock verilog syntax support for creating $ff cells
    - Added clk2fflogic


Yosys 0.5 .. Yosys 0.6
----------------------

 * Various
     - Added Contributor Covenant Code of Conduct
     - Various improvements in dict<> and pool<>
     - Added hashlib::mfp and refactored SigMap
     - Improved support for reals as module parameters
     - Various improvements in SMT2 back-end
     - Added "keep_hierarchy" attribute
     - Verilog front-end: define `BLACKBOX in -lib mode
     - Added API for converting internal cells to AIGs
     - Added ENABLE_LIBYOSYS Makefile option
     - Removed "techmap -share_map" (use "-map +/filename" instead)
     - Switched all Python scripts to Python 3
     - Added support for $display()/$write() and $finish() to Verilog front-end
     - Added "yosys-smtbmc" formal verification flow
     - Added options for clang sanitizers to Makefile

 * New commands and options
     - Added "scc -expect <N> -nofeedback"
     - Added "proc_dlatch"
     - Added "check"
     - Added "select %xe %cie %coe %M %C %R"
     - Added "sat -dump_json" (WaveJSON format)
     - Added "sat -tempinduct-baseonly -tempinduct-inductonly"
     - Added "sat -stepsize" and "sat -tempinduct-step"
     - Added "sat -show-regs -show-public -show-all"
     - Added "write_json" (Native Yosys JSON format)
     - Added "write_blif -attr"
     - Added "dffinit"
     - Added "chparam"
     - Added "muxcover"
     - Added "pmuxtree"
     - Added memory_bram "make_outreg" feature
     - Added "splice -wires"
     - Added "dff2dffe -direct-match"
     - Added simplemap $lut support
     - Added "read_blif"
     - Added "opt_share -share_all"
     - Added "aigmap"
     - Added "write_smt2 -mem -regs -wires"
     - Added "memory -nordff"
     - Added "write_smv"
     - Added "synth -nordff -noalumacc"
     - Added "rename -top new_name"
     - Added "opt_const -clkinv"
     - Added "synth -nofsm"
     - Added "miter -assert"
     - Added "read_verilog -noautowire"
     - Added "read_verilog -nodpi"
     - Added "tribuf"
     - Added "lut2mux"
     - Added "nlutmap"
     - Added "qwp"
     - Added "test_cell -noeval"
     - Added "edgetypes"
     - Added "equiv_struct"
     - Added "equiv_purge"
     - Added "equiv_mark"
     - Added "equiv_add -try -cell"
     - Added "singleton"
     - Added "abc -g -luts"
     - Added "torder"
     - Added "write_blif -cname"
     - Added "submod -copy"
     - Added "dffsr2dff"
     - Added "stat -liberty"

 * Synthesis metacommands
     - Various improvements in synth_xilinx
     - Added synth_ice40 and synth_greenpak4
     - Added "prep" metacommand for "synthesis lite"

 * Cell library changes
     - Added cell types to "help" system
     - Added $meminit cell type
     - Added $assume cell type
     - Added $_MUX4_, $_MUX8_, and $_MUX16_ cells
     - Added $tribuf and $_TBUF_ cell types
     - Added read-enable to memory model

 * YosysJS
     - Various improvements in emscripten build
     - Added alternative webworker-based JS API
     - Added a few example applications


Yosys 0.4 .. Yosys 0.5
----------------------

 * API changes
     - Added log_warning()
     - Added eval_select_args() and eval_select_op()
     - Added cell->known(), cell->input(portname), cell->output(portname)
     - Skip blackbox modules in design->selected_modules()
     - Replaced std::map<> and std::set<> with dict<> and pool<>
     - New SigSpec::extend() is what used to be SigSpec::extend_u0()
     - Added YS_OVERRIDE, YS_FINAL, YS_ATTRIBUTE, YS_NORETURN

 * Cell library changes
     - Added flip-flops with enable ($dffe etc.)
     - Added $equiv cells for equivalence checking framework

 * Various
     - Updated ABC to hg rev 61ad5f908c03
     - Added clock domain partitioning to ABC pass
     - Improved plugin building (see "yosys-config --build")
     - Added ENABLE_NDEBUG Makefile flag for high-performance builds
     - Added "yosys -d", "yosys -L" and other driver improvements
     - Added support for multi-bit (array) cell ports to "write_edif"
     - Now printing most output to stdout, not stderr
     - Added "onehot" attribute (set by "fsm_map")
     - Various performance improvements
     - Vastly improved Xilinx flow
     - Added "make unsintall"

 * Equivalence checking
     - Added equivalence checking commands:
         equiv_make equiv_simple equiv_status
	 equiv_induct equiv_miter
	 equiv_add equiv_remove

 * Block RAM support:
     - Added "memory_bram" command
     - Added BRAM support to Xilinx flow

 * Other New Commands and Options
     - Added "dff2dffe"
     - Added "fsm -encfile"
     - Added "dfflibmap -prepare"
     - Added "write_blid -unbuf -undef -blackbox"
     - Added "write_smt2" for writing SMT-LIBv2 files
     - Added "test_cell -w -muxdiv"
     - Added "select -read"


Yosys 0.3.0 .. Yosys 0.4
------------------------

 * Platform Support
     - Added support for mxe-based cross-builds for win32
     - Added sourcecode-export as VisualStudio project
     - Added experimental EMCC (JavaScript) support

 * Verilog Frontend
     - Added -sv option for SystemVerilog (and automatic *.sv file support)
     - Added support for real-valued constants and constant expressions
     - Added support for non-standard "via_celltype" attribute on task/func
     - Added support for non-standard "module mod_name(...);" syntax
     - Added support for non-standard """ macro bodies
     - Added support for array with more than one dimension
     - Added support for $readmemh and $readmemb
     - Added support for DPI functions

 * Changes in internal cell library
     - Added $shift and $shiftx cell types
     - Added $alu, $lcu, $fa and $macc cell types
     - Removed $bu0 and $safe_pmux cell types
     - $mem/$memwr WR_EN input is now a per-data-bit enable signal
     - Added $_NAND_ $_NOR_ $_XNOR_ $_AOI3_ $_OAI3_ $_AOI4_ $_OAI4_
     - Renamed ports of $lut cells (from I->O to A->Y)
     - Renamed $_INV_ to $_NOT_

 * Changes for simple synthesis flows
     - There is now a "synth" command with a recommended default script
     - Many improvements in synthesis of arithmetic functions to gates
	 - Multipliers and adders with many operands are using carry-save adder trees
         - Remaining adders are now implemented using Brent-Kung carry look-ahead adders
     - Various new high-level optimizations on RTL netlist
     - Various improvements in FSM optimization
     - Updated ABC to hg 5b5af75f1dda (from 2014-11-07)

 * Changes in internal APIs and RTLIL
     - Added log_id() and log_cell() helper functions
     - Added function-like cell creation helpers
     - Added GetSize() function (like .size() but with int)
     - Major refactoring of RTLIL::Module and related classes
     - Major refactoring of RTLIL::SigSpec and related classes
     - Now RTLIL::IdString is essentially an int
     - Added macros for code coverage counters
     - Added some Makefile magic for pretty make logs
     - Added "kernel/yosys.h" with all the core definitions
     - Changed a lot of code from FILE* to c++ streams
     - Added RTLIL::Monitor API and "trace" command
     - Added "Yosys" C++ namespace

 * Changes relevant to SAT solving
     - Added ezSAT::keep_cnf() and ezSAT::non_incremental()
     - Added native ezSAT support for vector shift ops
     - Updated MiniSAT to git 37dc6c67e2 (from 2013-09-25)

 * New commands (or large improvements to commands)
     - Added "synth" command with default script
     - Added "share" (finally some real resource sharing)
     - Added "memory_share" (reduce number of ports on memories)
     - Added "wreduce" and "alumacc" commands
     - Added "opt -keepdc -fine -full -fast"
     - Added some "test_*" commands

 * Various other changes
     - Added %D and %c select operators
     - Added support for labels in yosys scripts
     - Added support for here-documents in yosys scripts
     - Support "+/" prefix for files from proc_share_dir
     - Added "autoidx" statement to ilang language
     - Switched from "yosys-svgviewer" to "xdot"
     - Renamed "stdcells.v" to "techmap.v"
     - Various bug fixes and small improvements
     - Improved welcome and bye messages


Yosys 0.2.0 .. Yosys 0.3.0
--------------------------

 * Driver program and overall behavior:
     - Added "design -push" and "design -pop"
     - Added "tee" command for redirecting log output

 * Changes in the internal cell library:
     - Added $dlatchsr and $_DLATCHSR_???_ cell types

 * Improvements in Verilog frontend:
     - Improved support for const functions (case, always, repeat)
     - The generate..endgenerate keywords are now optional
     - Added support for arrays of module instances
     - Added support for "`default_nettype" directive
     - Added support for "`line" directive

 * Other front- and back-ends:
     - Various changes to "write_blif" options
     - Various improvements in EDIF backend
     - Added "vhdl2verilog" pseudo-front-end
     - Added "verific" pseudo-front-end

 * Improvements in technology mapping:
     - Added support for recursive techmap
     - Added CONSTMSK and CONSTVAL features to techmap
     - Added _TECHMAP_CONNMAP_*_ feature to techmap
     - Added _TECHMAP_REPLACE_ feature to techmap
     - Added "connwrappers" command for wrap-extract-unwrap method
     - Added "extract -map %<design_name>" feature
     - Added "extract -ignore_param ..." and "extract -ignore_parameters"
     - Added "techmap -max_iter" option

 * Improvements to "eval" and "sat" framework:
     - Now include a copy of Minisat (with build fixes applied)
     - Switched to Minisat::SimpSolver as SAT back-end
     - Added "sat -dump_vcd" feature
     - Added "sat -dump_cnf" feature
     - Added "sat -initsteps <N>" feature
     - Added "freduce -stop <N>" feature
     - Added "freduce -dump <prefix>" feature

 * Integration with ABC:
     - Updated ABC rev to 7600ffb9340c

 * Improvements in the internal APIs:
     - Added RTLIL::Module::add... helper methods
     - Various build fixes for OSX (Darwin) and OpenBSD


Yosys 0.1.0 .. Yosys 0.2.0
--------------------------

 * Changes to the driver program:
     - Added "yosys -h" and "yosys -H"
     - Added support for backslash line continuation in scripts
     - Added support for #-comments in same line as command
     - Added "echo" and "log" commands

 * Improvements in Verilog frontend:
     - Added support for local registers in named blocks
     - Added support for "case" in "generate" blocks
     - Added support for $clog2 system function
     - Added support for basic SystemVerilog assert statements
     - Added preprocessor support for macro arguments
     - Added preprocessor support for `elsif statement
     - Added "verilog_defaults" command
     - Added read_verilog -icells option
     - Added support for constant sizes from parameters
     - Added "read_verilog -setattr"
     - Added support for function returning 'integer'
     - Added limited support for function calls in parameter values
     - Added "read_verilog -defer" to suppress evaluation of modules with default parameters

 * Other front- and back-ends:
     - Added BTOR backend
     - Added Liberty frontend

 * Improvements in technology mapping:
     - The "dfflibmap" command now strongly prefers solutions with
           no inverters in clock paths
     - The "dfflibmap" command now prefers cells with smaller area
     - Added support for multiple -map options to techmap
     - Added "dfflibmap" support for //-comments in liberty files
     - Added "memory_unpack" command to revert "memory_collect"
     - Added standard techmap rule "techmap -share_map pmux2mux.v"
     - Added "iopadmap -bits"
     - Added "setundef" command
     - Added "hilomap" command

 * Changes in the internal cell library:
     - Major rewrite of simlib.v for better compatibility with other tools
     - Added PRIORITY parameter to $memwr cells
     - Added TRANSPARENT parameter to $memrd cells
     - Added RD_TRANSPARENT parameter to $mem cells
     - Added $bu0 cell (always 0-extend, even undef MSB)
     - Added $assert cell type
     - Added $slice and $concat cell types

 * Integration with ABC:
     - Updated ABC to hg rev 2058c8ccea68
     - Tighter integration of ABC build with Yosys build. The make
           targets 'make abc' and 'make install-abc' are now obsolete.
     - Added support for passing FFs from one clock domain through ABC
     - Now always use BLIF as exchange format with ABC
     - Added support for "abc -script +<command_sequence>"
     - Improved standard ABC recipe
     - Added support for "keep" attribute to abc command
     - Added "abc -dff / -clk / -keepff" options

 * Improvements to "eval" and "sat" framework:
     - Added support for "0" and "~0" in right-hand side -set expressions
     - Added "eval -set-undef" and "eval -table"
     - Added "sat -set-init" and "sat -set-init-*" for sequential problems
     - Added undef support to SAT solver, incl. various new "sat" options
     - Added correct support for === and !== for "eval" and "sat"
     - Added "sat -tempinduct" (default -seq is now non-induction sequential)
     - Added "sat -prove-asserts"
     - Complete rewrite of the 'freduce' command
     - Added "miter" command
     - Added "sat -show-inputs" and "sat -show-outputs"
     - Added "sat -ignore_unknown_cells" (now produce an error by default)
     - Added "sat -falsify"
     - Now "sat -verify" and "sat -falsify" can also be used without "-prove"
     - Added "expose" command
     - Added support for @<sel_name> to sat and eval signal expressions

 * Changes in the 'make test' framework and auxiliary test tools:
     - Added autotest.sh -p and -f options
     - Replaced autotest.sh ISIM support with XSIM support
     - Added test cases for SAT framework

 * Added "abbreviated IDs":
     - Now $<something>$foo can be abbreviated as $foo.
     - Usually this last part is a unique id (from RTLIL::autoidx)
     - This abbreviated IDs are now also used in "show" output

 * Other changes to selection framework:
     - Now */ is optional in */<mode>:<arg> expressions
     - Added "select -assert-none" and "select -assert-any"
     - Added support for matching modules by attribute (A:<expr>)
     - Added "select -none"
     - Added support for r:<expr> pattern for matching cell parameters
     - Added support for !=, <, <=, >=, > for attribute and parameter matching
     - Added support for %s for selecting sub-modules
     - Added support for %m for expanding selections to whole modules
     - Added support for i:*, o:* and x:* pattern for selecting module ports
     - Added support for s:<expr> pattern for matching wire width
     - Added support for %a operation to select wire aliases

 * Various other changes to commands and options:
     - The "ls" command now supports wildcards
     - Added "show -pause" and "show -format dot"
     - Added "show -color" support for cells
     - Added "show -label" and "show -notitle"
     - Added "dump -m" and "dump -n"
     - Added "history" command
     - Added "rename -hide"
     - Added "connect" command
     - Added "splitnets -driver"
     - Added "opt_const -mux_undef"
     - Added "opt_const -mux_bool"
     - Added "opt_const -undriven"
     - Added "opt -mux_undef -mux_bool -undriven -purge"
     - Added "hierarchy -libdir"
     - Added "hierarchy -purge_lib" (by default now do not remove lib cells)
     - Added "delete" command
     - Added "dump -append"
     - Added "setattr" and "setparam" commands
     - Added "design -stash/-copy-from/-copy-to"
     - Added "copy" command
     - Added "splice" command