Taichi

Highlights:
- **Bug fixes**
- Use sys.getfilesystemencoding() to prevent possible locale errors (1775) (by **彭于斌**)
- **C source backend**
- Support AdStack on C backend (1752) (by **彭于斌**)
- **Documentation**
- Add how to set environment variables for fish users (1800) (by **Luyu Cheng**)
- Separate arithmetics.rst from syntax.rst and fill it with more details (1761) (by **彭于斌**)
- **Examples**
- Fix stable_fluid.py boundary broken: int -> ti.floor, and make mpm3d.py 3x faster on CUDA (1784) (by **彭于斌**)
- **Language and syntax**
- Support formatted string with args in assert (1806) (by **Ye Kuang**)
- Support printing lists and tuples in Taichi-scope (1796) (by **彭于斌**)
- Add ti.get_rel_eps() for maximal relative error tolerance on current backend (1798) (by **Ye Kuang**)
- Support querying external array shape by 'x.shape' (1787) (by **thinking-tower**)
- **IR optimization passes**
- Make irpass::replace_all_usages_with bottom-up (1789) (by **xumingkuan**)

Full changelog:
- [misc] Remove unused code/comments in transforms/simpilfy.cpp (1812) (by **Yuanming Hu**)
- [ir] Fix irpass::analysis::clone on TLS/BLS prologue/epilogue (1811) (by **Yuanming Hu**)
- [error] "Better error message when vector used as if's condition variable (1804)" (1810) (by **彭于斌**)
- [Lang] Support formatted string with args in assert (1806) (by **Ye Kuang**)
- [refactor] Replace std::map with switch case statements in lang_util.cpp (1755) (by **Aryan Soman**)
- [misc] Revert "Better error message when vector used as if's condition variable (1804)" (1808) (by **Yuanming Hu**)
- [error] Better error message when vector used as if's condition variable (1804) (by **彭于斌**)
- [Opt] Make irpass::replace_all_usages_with bottom-up (1789) (by **xumingkuan**)
- [Doc] Add how to set environment variables for fish users (1800) (by **Luyu Cheng**)
- [CC] [autodiff] Support AdStack on C backend (1752) (by **彭于斌**)
- [Lang] Support printing lists and tuples in Taichi-scope (1796) (by **彭于斌**)
- [workflow] import missing package sys in code_format.py (1802) (by **Luyu Cheng**)
- [cli] Add path to Python executable to 'ti diagnose' (1801) (by **Luyu Cheng**)
- [refactor] Remove the singleton Program::context (1799) (by **Ye Kuang**)
- [ir] Restore verification for OffloadedStmt (1790) (by **xumingkuan**)
- [Lang] [test] Add ti.get_rel_eps() for maximal relative error tolerance on current backend (1798) (by **Ye Kuang**)
- [Lang] [ir] Support querying external array shape by 'x.shape' (1787) (by **thinking-tower**)
- [workflow] Travis CI only test Python 3.6 unless release tag is used (1793) (by **彭于斌**)
- [refactor] Move Context to taichi/program (1788) (by **Ye Kuang**)
- [doc] Better clarify the difference between two profilers (1759) (by **彭于斌**)
- [ir] [autodiff] Initialize ADStack with a zero (1791) (by **Yuanming Hu**)
- [ir] [opt] Unify ifloordiv implementation over backends in demote_operations (1771) (by **彭于斌**)
- [Bug] [misc] Use sys.getfilesystemencoding() to prevent possible locale errors (1775) (by **彭于斌**)
- [Example] Fix stable_fluid.py boundary broken: int -> ti.floor, and make mpm3d.py 3x faster on CUDA (1784) (by **彭于斌**)
- [test] Expand the tolerance for testing on metal backend (1779) (by **Xudong Feng**)
- [opt] Simplify identical load elimination (1782) (by **xumingkuan**)
- [error] [opengl] Better error message when int64 or sparse SNode not supported for OpenGL (1783) (by **彭于斌**)
- [Doc] Separate arithmetics.rst from syntax.rst and fill it with more details (1761) (by **彭于斌**)
- [ipython] Separate {Expr,Matrix}.{__str__,__repr__} to prevent unexpected materialization when repr (1766) (by **彭于斌**)
- [async] Support constant folding in async mode (1778) (by **Ye Kuang**)
- [workflow] [cli] Improve coverage of 'ti format' and 'ti format_all' (1768) (by **彭于斌**)
- [misc] Add "make_block_local" option to "CompileConfig" (1727) (by **Yuanming Hu**)

Highlights:
- **Command line interface**
- Add 'ti repl' command for Taichi REPL shell (1765) (by **彭于斌**)
- **GUI**
- Support gui.arrow_field() and gui.point_field() for small resolution vector / scalar field visualization (1763) (by **彭于斌**)
- **Intermediate representation**
- Support SAR operator: x >> y (1772) (by **Hanke Liu**)
- Support SHL operator: x << y (1762) (by **Xuanda Yang**)
- **Refactor**
- ti.classfunc and ti.classkernel are obsolete. Directly use ti.func and ti.kernel instead (1770) (by **彭于斌**)
- 'ti.var' is deprecated, use 'ti.field' instead (1767) (by **彭于斌**)

Full changelog:
- [CLI] [doc] Add 'ti repl' command for Taichi REPL shell (1765) (by **彭于斌**)
- [IR] [lang] Support SAR operator: x >> y (1772) (by **Hanke Liu**)
- [async] [benchmark] Enable optimization for global variables after fusion (1776) (by **xumingkuan**)
- [benchmark] [async] Improve AsyncEngine benchmarks (1774) (by **Yuanming Hu**)
- [GUI] Support gui.arrow_field() and gui.point_field() for small resolution vector / scalar field visualization (1763) (by **彭于斌**)
- [Refactor] ti.classfunc and ti.classkernel are obsolete. Directly use ti.func and ti.kernel instead (1770) (by **彭于斌**)
- [IR] [lang] Support SHL operator: x << y (1762) (by **Xuanda Yang**)
- [Refactor] 'ti.var' is deprecated, use 'ti.field' instead (1767) (by **彭于斌**)
- [benchmark] [async] Improve AsyncEngine benchmarks (1758) (by **Yuanming Hu**)
- [misc] Fix a typo in README.md (1760) (by **fq**)
- [benchmark] [async] Add ti.benchmark_plot and add fuse_dense.py to benchmarks (1754) (by **xumingkuan**)

Highlights:
- **Error messages**
- Attach a traceback to ti.field when 'Some variable(s) are not placed' (1734) (by **彭于斌**)
- **Examples**
- Upgrade mass_spring_3d.py to Taichi THREE v0.0.3 API (1732) (by **彭于斌**)
- **GUI**
- Add handy ti.imscale(img, w, h) for scaling image (1735) (by **彭于斌**)
- **IR optimization passes**
- Identical store/load elimination by control-flow graph (1741) (by **xumingkuan**)

Full changelog:
- [GUI] Add handy ti.imscale(img, w, h) for scaling image (1735) (by **彭于斌**)
- [benchmark] [async] Add more statistics for async benchmark (1747) (by **xumingkuan**)
- [misc] Fix OffloadedStmt cloning (1745) (by **Yuanming Hu**)
- [refactor] Use condition variable instead of sleep in ParallelExecutor (1743) (by **Ye Kuang**)
- [cc] [refactor] C backend use result_buffer for return value too (1736) (by **彭于斌**)
- [Error] Attach a traceback to ti.field when 'Some variable(s) are not placed' (1734) (by **彭于斌**)
- [benchmark] Dump the benchmark data into one yaml file (1744) (by **xumingkuan**)
- [benchmark] Upgrade "benchmarks" to new syntax (1729) (by **Xudong Feng**)
- [misc] Upgrade "misc" to the new syntax (1730) (by **Xudong Feng**)
- [misc] Create misc/examples.md for more examples (1726) (by **Yuanming Hu**)
- [opt] Add irpass::analysis::same_value (1742) (by **xumingkuan**)
- [Opt] Identical store/load elimination by control-flow graph (1741) (by **xumingkuan**)
- [example] Upgrade pbf2d.py to new syntax (1710) (by **彭于斌**)
- [Example] Upgrade mass_spring_3d.py to Taichi THREE v0.0.3 API (1732) (by **彭于斌**)

Highlights:
- **Documentation**
- Add API reference for external array interactions (1677) (by **彭于斌**)
- **Language and syntax**
- Support printing scalar fields in Python-scope (1701) (by **彭于斌**)

Full changelog:
- [cuda] Refactor CUDA kernel launching (1738) (by **Yuanming Hu**)
- [blender] [example] Fix examples/waterwave.py memory leakage in Blender (1733) (by **彭于斌**)
- [refactor] Add Kernel::LaunchContextBuilder skeleton code (1723) (by **Ye Kuang**)
- [opengl] [refactor] Use result_buffer for return value since k-ye insist to (1724) (by **彭于斌**)
- [Lang] Support printing scalar fields in Python-scope (1701) (by **彭于斌**)
- [misc] Reformat all the files and rename "type_check" & "lower_ast" (1728) (by **Taichi Gardener**)
- [misc] Rename "fully_deprecated" to "obsolete" (1725) (by **Yuanming Hu**)
- [misc] [refactor] Replace the word tensor by field in comments and error messages (1721) (by **彭于斌**)
- [opengl] Cache GL_MAX_COMPUTE_WORK_GROUP_INVOCATIONS value to prevent glGetInteger per-launch (1718) (by **彭于斌**)
- [example] [refactor] Replace global field ti.Vector -> ti.Vector.field in examples (1716) (by **Xudong Feng**)
- [pypi] Upgrade sourceinspect to 0.0.3 for hot fixes (1717) (by **彭于斌**)
- [example] Make jacobi iteration 2x faster in stable_fluid.py (1713) (by **彭于斌**)
- [example] [refactor] Replace all ti.var->ti.field in our examples (1712) (by **Xudong Feng**)
- [metal] Pass back return values via result_buffer (1709) (by **Ye Kuang**)
- [refactor] Fix missed ti.var -> ti.field refactors in codebase (1705) (by **彭于斌**)
- [Doc] Add API reference for external array interactions (1677) (by **彭于斌**)
- [cli] [workflow] Support "\r\n" -> "\n" convert in "ti format" command (1706) (by **彭于斌**)

Highlights:
- **C source backend**
- Release the C backend (1707) (by **彭于斌**)
- **Documentation**
- Typo and grammatical fixes in vector documentation (1695) (by **Aryan Soman**)
- **Sparse computation**
- Support memory profiling for LLVM backends (1655) (by **Yuanming Hu**)

Full changelog:
- [mac] Add NSAutoreleasePool to manage obj-c objects' lifetime (1704) (by **Ye Kuang**)
- [CC] Release the C backend (1707) (by **彭于斌**)
- [test] [refactor] Replace ti.Vector or ti.Vector.var -> ti.Vector.field (1698) (by **Xudong Feng**)
- [example] [misc] Add 'ti.taichi_logo' function & misc typo fix (1640) (by **彭于斌**)
- [metal] Log errors if the compute kernel compilation failed (1697) (by **Ye Kuang**)
- [test] Fix Torch IO test (1700) (by **Yuanming Hu**)
- [misc] Update README.md gallery for the newly added examples during GAMES 201 (1652) (by **彭于斌**)
- [test] [refactor] Replace global field ti.Matrix or ti.Matrix.var -> ti.Matrix.field in python tests (1694) (by **Xudong Feng**)
- [Doc] Typo and grammatical fixes in vector documentation (1695) (by **Aryan Soman**)
- [example] [refactor] Upgrade to ti.field syntax for many examples (1669) (by **彭于斌**)
- [test] Replace ti.var by ti.field in tests starting with r-z (1684) (by **Xudong Feng**)
- [async] [cuda] AsyncEngine now supports CUDA (1687) (by **Yuanming Hu**)
- [Sparse] [llvm] Support memory profiling for LLVM backends (1655) (by **Yuanming Hu**)

Highlights:
- **Documentation**
- Improve Taichi kernels and functions definition (1576) (by **彭于斌**)
- **Examples**
- Add mpm3d.py for dimension-independent MPM method (1639) (by **彭于斌**)
- **IPython and other shells**
- Use 'sourceinspect' to support Blender scripting module and IDLE shell (1664) (by **彭于斌**)

Full changelog:
- [Example] Add mpm3d.py for dimension-independent MPM method (1639) (by **彭于斌**)
- [misc] Prevent 'supported_archs()' invocation in 'adaptive_arch_select()' for better compatibility (1666) (by **彭于斌**)
- [test] Replace ti.var by ti.field in tests starting with h-q (1683) (by **Xudong Feng**)
- [test] Replace ti.var by ti.field in tests starting with a-g (1681) (by **Xudong Feng**)
- Turn on the CC backend in the Dockerfile (1680) (by **samuela**)
- [llvm] Obsolete LLVM 8 support (1685) (by **Yuanming Hu**)
- [Doc] [refactor] Improve Taichi kernels and functions definition (1576) (by **彭于斌**)
- [cli] Add 'ti diagnose' command for providing system informations (1671) (by **彭于斌**)
- [cc] Add ti.cfg.cc_compile_cmd and ti.cfg.cc_link_cmd (1645) (by **彭于斌**)
- [IPython] Use 'sourceinspect' to support Blender scripting module and IDLE shell (1664) (by **彭于斌**)
- [misc] Add links to the mirror repo in Gitee (1665) (by **彭于斌**)
- [misc] Update doc version (1672) (by **Yuanming Hu**)
- [misc] [refactor] Add fully_deprecated mark for future use (1656) (by **彭于斌**)
- [doc] Fix uncovered while deprecated term 'tensor' occurance (1653) (by **彭于斌**)