spirv-scf.mlir

// Option#1: use sequence of blocks
//   Missing all goodies for regions :(

// Option#2: use scf dialect for scf
//   Missing story inside spirv; hard to deserialize from blob :(

// Option#3: flesh out spirv scf ops: introduce new terminators:
// - spv.mlir.fallthrough  // jump to the next region
// - spv.mlir.condition    // jump to the next region if true; jump out of the current scf op if false
// - spv.mlir.merge        // jump out of the current scf op
// - spv.mlir.reenter      // jump back to the current scf op's header region

// - spv.mlir.break        // jump out of the parent scf op
// - spv.mlir.continue     // jump to the parent scf op's continue region

// Design considerations:
// * How easy to convert from HLSL
// * How easy to convert to SPIR-V proper
// * How easy to convert from SPIR-V proper
// * How resilient w.r.t. transformations

// condition

if (condition) {
} else {
}

spv.mlir.selection (%condition)
  then = {
    // ...
    spv.mlir.merge
  }
  else = {
    // ...
    spv.mlir.merge
  }

// switch

switch (selector) {
case case1: /* ... */ break;
case case2: /* ... */ // fallthrough;
default: ...
}

spv.mlir.switch (%selector)
  case1 = {
    // ...
    spv.mlir.merge
  }
  case2 = {
    // ...
    spv.mlir.fallthrough
  }
  default = {
    // ...
    spv.mlir.merge
  }

// loop

while (cond) {
}

spv.mlir.loop
  header = {
    // Compute condition
    spv.mlir.condition(%condition)
  }
  body = {
    // Main logic
    spv.mlir.fallthrough // to continue region
  }
  continue = {
    // Nothing else
    spv.mlir.reenter // back to header region
  }

do {
} while (cond);

spv.mlir.loop
  header = {
    // Main logic
    // Compute condition
    spv.mlir.condition(%condition)
  }
  body = {
    // Nothing else
    spv.mlir.fallthrough // to continue region
  }
  continue = {
    // Nothing else
    spv.mlir.reenter // back to header region
  }
  
for (int i = 0; i < N; ++i) {
}
  
spv.mlir.loop
  header = {
    // Compute condition: i < N
    spv.mlir.condition(%condition)
  }
  body = {
    // Main logic
    spv.mlir.fallthrough // to continue region
  }
  continue = {
    // ++i
    spv.mlir.reenter // back to header region
  }
  
// Cases

for(int i = 0; i < 10; ++i) {
  if (cond) {
    foo();
    continue;
  }
}

spv.mlir.loop
  header = {
    // Compute condition: i < 10
    spv.mlir.condition(%condition)
  }
  body = {
    spv.mlir.selection (%condition)
      then = {
        // foo()
        spv.mlir.continue // to continue region
      }
      else = {
      }
    spv.mlir.fallthrough // to continue region
  }
  continue = {
    // ++i
    spv.mlir.reenter // back to header region
  }
  
// phi: using block arguments