# IRDL  [paper (PDF)](https://dl.acm.org/doi/pdf/10.1145/3519939.3523700), [talk (youtube)](https://www.youtube.com/watch?v=uKXv1Cc_Pgs) --- ### Why? Too many IRs! ```plaintext Swift ----> SIL-IR --------+ | C/C++ ---------------------+-----> LLVM ----> machine code | Rust ----> HIR ---> MIR --+ ``` --- ### (You are like little baby, watch this) ```plaintext Swift ----> SIL-IR --------+ | C/C++ ---------------------+-----> LLVM ----> machine code | ^ ^ Rust ----> HIR ---> MIR --+ | | | | | | Haskell --> Core --> STG ---> Cmm ---+--> NCG ---+ ``` --- ### On a smaller scale ```plaintext LQC ---> Burn Semantics ---> Burn Assembly ---> TAC --+ | | | Interpreted by Burninator <--- Burn Config <---+ ``` --- ### Usual Cost of Adding a New IR * Custom IR * Parser * Printer * Pass manager * Dead code elimination * Peephole optimizations --- ### Cost of Adding a New IR (for us) * Custom IR * ~~Parser~~ * Printer (probably, debugging) * ~~Pass manager~~ * Dead code elimination _sometimes_ * Peephole optimizations _sometimes_ --- ### Recent development: MLIR _Multi-Level Intermediate Representation_ <img src="https://i.imgur.com/Ztwh8xX.png" width="600px" /> --- _Only problem you can't solve with more languages is too many languages_ --- ### What MLIR Solves * Custom IR * ~~Parser~~ * ~~Printer~~ * ~~Pass manager~~ * ~~Dead code elim~~ * ~~Peephole optimizations~~ --- ### Problem? _gotta use C++_ <img src="https://i.imgur.com/U6xhwxN.png" width="400px" /> --- ### Existing Solutions * TableGen - legacy LLVM framework <!-- generic boilerplate, mostly backend --> * ODS - Operator Definition Specification, used by MLIR, built on TableGen, incomplete --- ### (Proposed) Solution: IRDL _IRDL: An IR Definition Language for SSA Compilers_ --- ### Designed, Principled * Everything is a Constraint or an Operation * Types, Aliases => Constraints * Instructions, Regions, Literals => Operations --- _A collection of Constraints and Operations is a Dialect_ --- ### Example: Complex Math ```c++ Dialect cmath { Alias !FloatType = !AnyOf<!f32, !f64> Type complex { Parameters (elementType: !FloatType) Summary "A complex number" } Operation mul { ConstraintVar (!T: !complex<FloatType>) Operands (lhs: !T, rhs: !T) Results (res: !T) Format "$lhs, $rhs : $T.elementType" Summary "Multiply two complex numbers" } } ``` --- ### Constraint Composition Usual logical AND/OR/NOT ```c++ Alias NonZero = !And<int32_t, !Not<0 : int32_t>> Alias Integer = !AnyOf<int32_t, int64_t> Alias Float = !AnyOf<f32, f64> Alias Number = !AnyOf<!Integer, !Float> ``` --- ### Literals in Constraints Limited use of literals and enums in constraints ```c++ Enum signedness { Signless, Signed, Unsigned } Type integer { Parameters (bitwidth: uint32_t, signed: signedness) } Alias signed_integer = !integer<uint32_t, signedness.Signed> ``` Dependent types, plz --- ### Control Flow ```c++ Operation range_loop_done {} Operation range_loop { Operands (start: !i32, stop: !i32, step: !i32) Region body { Arguments (i: !i32) Terminator range_loop_done } } ``` `Terminator` means body must be a single BB --- ### Control Flow ```c++ Operation conditional_branch { Operands (condition: !i1) // 1 bit bools are cute Successors (true_branch, false_branch) // basic blocks } ``` --- ### C++ Escape Hatch ```c++ Constraint Size : uint32_t { Summary "integer value between 0 and 32" CppConstraint "$_self <= 32" } Type SizedVec { Parameters (typ: !AnyType, size: Size) } Operation append_vec { ConstraintVars (T: !AnyType) Operands (lhs: SizedVec<T, Size>, rhs: SizedVec<T, Size>) Results (res: SizedVec<T, Size>) CppConstraint "$_self.lhs().size() + $_self.rhs().size() == $_self.res().size()" } ``` --- ### Big Punchline LLVM MLIR: 942 ops over 28 IR dialects IRDL can represent 97% of them directly The remainder require minimal C++ --- ### Cool How Do I Use It _Bad news_: [it's currently a branch in a fork of LLVM](https://github.com/opencompl/llvm-project/pull/1) :cry: --- ### Links * [IRDL Paper](https://dl.acm.org/doi/pdf/10.1145/3519939.3523700) * [PLDI Talk](https://www.youtube.com/watch?v=uKXv1Cc_Pgs), ~16 mins * [IRDL @ MLIR Open Developer Meeting](https://www.youtube.com/watch?v=SlCXx5IFV40), ~1 hour * [Older MLIR Paper](https://arxiv.org/pdf/2002.11054.pdf) --- --- ### Different Ways I've Typed IRDL Today * IRDL * IDRL * IDLR * IRBL