Add license and README

Author: nmraz

LICENSE

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+MIT License
+
+Copyright (c) 2023 Noam Raz
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Spidir
+
+WIP JIT library written in Rust with the following goals:
+
+- Embeddability: Spidir is completely freestanding and requires only a memory allocator
+- Simple C API: The intended way to embed/consume Spidir, though the unstable internal Rust APIs can be used as well
+- Reasonable optimization quality: Higher-level language runtimes using Spidir as a backend should eventually be able to expect decent codegen
+
+Spidir was originally created for use in [TomatoDotNet](https://github.com/TomatOrg/TomatoDotNet/), so feature development is guided primarily by the needs of that project.
+
+## Using Spidir
+
+See the `c-api-tests` directory for example programs embedding the C API.
+
+All important functionality is exposed via the CLI binary `spidirtool`, which can be used to:
+
+- Graph the IR using graphviz
+- Inspect internal state
+- Generate/execute code for a given IR module
+
+See
+
+```
+cargo run -p spidirtool help
+```
+
+for more information.
+
+## IR
+
+Spidir uses two intermediate representations internally:
+
+- Spidir: target-independent IR for high-level optimizations
+  - SSA-based sea-of-nodes representation
+  - Uses phi nodes to model dataflow merges (easier to integrate in a sea-of-nodes setup)
+- LIR (linear IR): target-dependent IR used after instruction selection
+  - Flat list of instructions with CFG information stored separately
+  - Still in SSA form, but uses block parameters instead of phi nodes (more elegant for block-based IRs)
+  - Used by register allocator and final code emission
+
+These are abstracted away by the C construction API, which provides a simple block-based facade over the sea-of-nodes graph.
+
+## Implementation Status
+
+### Implemented
+
+- Miscellaneous:
+
+  - C bindings: IR construction/dumping/optimization/codegen
+  - IR text format/parser for testing and debugging
+  - IR verifier
+
+- IR features:
+
+  - Basic integer arithmetic/bitwise instructions
+  - Loads/stores
+  - Basic control flow (conditional branches)
+  - Internal/external/indirect calls
+  - External functions
+  - Stack slots
+
+- Codegen:
+
+  - Basic x64 backend
+  - Hopefully-intelligent register allocator
+    - Live range splitting
+    - Rematerialization
+    - Symbolic verifier
+
+- Optimization:
+
+  - Global code motion
+  - Simple canonicalization/GVN
+
+### Planned
+
+- IR:
+
+  - Memory operations (`memset`, `memcpy`, etc.)
+  - Bit-counting operations
+  - External globals
+  - Cold block annotation
+  - Floating point support
+  - Unwinding support
+  - Jump tables
+  - Static branch/patchpoint support
+
+- Codegen:
+
+  - Improved x64 instruction selection
+  - Minor register allocator improvements
+    - Use 3-address instructions instead of copies where possible
+    - Improved redundant copy elimination?
+
+- Optimization:
+  - Improved local block scheduling
+  - SROA
+  - SCCP
+  - Jump threading
+  - Range check elimination
+
+## Projects Using Spidir
+
+- [TomatoDotNet](https://github.com/TomatOrg/TomatoDotNet/), a freestanding C# runtime (original project motivation)
+- [spidir-wasm](https://github.com/Itay2805/spidir-wasm/), a small WASM implementation showcasing the C API