CoreDSLToLLVM for GlobalISel

This repo implements an LLVM-based tool for automatic generation of Instruction Selection Patterns for GlobalISel. Patterns are generated from CoreDSL2 descriptions of instruction behavior.

The original version of this tool (targeting LLVM ISelDAG) was written for my Bachelor's Thesis at TUM.

Build Process

Everything is tied into the LLVM build system. Generally:

1. Clone the repo and cd into it.
2. mkdir llvm/build && cd llvm/build
3. cmake ..
4. cmake --build .

Usage

Pattern Generation is implemented as an additional LLVM tool (pattern-gen) within the LLVM tree. Run ./llvm/build/bin/pattern-gen core_descs/Example.core_desc to generate a pattern for an example instruction.

Example

CoreDSL2 Instruction Description

CV_SUBINCACC {
  encoding: 7'b0101000 :: 5'b00000 :: rs1[4:0] :: 3'b011 :: rd[4:0] :: 7'b0101011;
  assembly: "{name(rd)}, {name(rs1)}";
  behavior: {
    if (rd != 0) {
      X[rd] += X[rs1] - X[rs2] + 1;
    }
  }
}

LLVM-IR

define void @implCV_SUBINCACC(ptr noalias nocapture %rd, ptr nocapture readonly %rs1, ptr nocapture readonly %rs2, i32 %imm, i32 %imm2) local_unnamed_addr #0 {
  %rs1.v = load i32, ptr %rs1, align 4
  %rs2.v = load i32, ptr %rs2, align 4
  %rd.v = load i32, ptr %rd, align 4
  %1 = add i32 %rs1.v, 1
  %2 = sub i32 %1, %rs2.v
  %3 = add i32 %2, %rd.v
  store i32 %3, ptr %rd, align 4
  ret void
}

pre-ISel MIR

bb.1 (%ir-block.0):
  liveins: $x10, $x11, $x12, $x13, $x14
  %0:gprb(p0) = COPY $x10
  %1:gprb(p0) = COPY $x11
  %2:gprb(p0) = COPY $x12
  %3:gprb(s32) = COPY $x13
  %4:gprb(s32) = COPY $x14
  %8:gprb(s32) = G_CONSTANT i32 1
  %5:gprb(s32) = G_LOAD %1:gprb(p0) :: (load (s32) from %ir.rs1)
  %6:gprb(s32) = G_LOAD %2:gprb(p0) :: (load (s32) from %ir.rs2)
  %7:gprb(s32) = G_LOAD %0:gprb(p0) :: (load (s32) from %ir.rd)
  %9:gprb(s32) = G_ADD %5:gprb, %8:gprb
  %10:gprb(s32) = G_SUB %9:gprb, %6:gprb
  %11:gprb(s32) = G_ADD %10:gprb, %7:gprb
  G_STORE %11:gprb(s32), %0:gprb(p0) :: (store (s32) into %ir.rd)
  PseudoRET

Generated Pattern

def : Pat<
  (add (sub (add GPR:$rs1, (i32 1)), GPR:$rs2), GPR:$rd),
  (CV_SUBINCACC_S_S_S_S GPR:$rd, GPR:$rs1, GPR:$rs2)>;