Hi all,
I’m trying to use the convert-scf-to-spirv pass in MLIR to lower the (scf.for) in the following toy example to spirv.mlir.loop.
func.func @forward() {
%c0 = arith.constant 0 : index
%c32 = arith.constant 32 : index
%c1 = arith.constant 1 : index
scf.for %arg2 = %c0 to %c32 step %c1 {
%1 = index.add %arg2, %arg2
}
return
}
However, I run into the following error
error: failed to materialize conversion for block argument #0 that remained live after conversion, type was 'index', with target type 'i32' origArg: <block argument> of type 'index' at index: 0 newArg: <<NULL VALUE>>see existing live user here: %8 = "index.add"(<<UNKNOWN SSA VALUE>>, <<UNKNOWN SSA VALUE>>) : (index, index) -> index
scf.for %arg2 = %c0 to %c32 step %c1 {
^
/nn-mlir/test-scf-to-spirv.mlir:6:14: note: see existing live user here: %8 = "index.add"(<<UNKNOWN SSA VALUE>>, <<UNKNOWN SSA VALUE>>) : (index, index) -> index
%1 = index.add %arg2, %arg2
which I believe has to do with the fact that index.add expects the operands to be of type index and during the conversion of scf.for to spirv.mlir.loop, the index gets converted to an i32 and so, there is no way to pass an index to index.add.
However, even if I add
auto addUnrealizedCast = [](OpBuilder &builder, Type type,
ValueRange inputs, Location loc) {
auto cast = builder.create<UnrealizedConversionCastOp>(loc, type, inputs);
return std::optional<Value>(cast.getResult(0));
};
typeConverter.addSourceMaterialization(addUnrealizedCast);
typeConverter.addTargetMaterialization(addUnrealizedCast);
target->addLegalOp<UnrealizedConversionCastOp>();
to SCFToSPIRVPass::runOnOperation(), I would expect the resulting IR to look something like
module {
spirv.func @forward() "None" {
%cst0_i32 = spirv.Constant 0 : i32
%cst32_i32 = spirv.Constant 32 : i32
%cst1_i32 = spirv.Constant 1 : i32
spirv.mlir.loop {
spirv.Branch ^bb1(%cst0_i32 : i32)
^bb1(%0: i32): // 2 preds: ^bb0, ^bb2
%1 = spirv.SLessThan %0, %cst32_i32 : i32
spirv.BranchConditional %1, ^bb2, ^bb3
^bb2: // pred: ^bb1
%cast_to_index = builtin.unrealized_conversion_cast %0 : i32 to index
%index_add = index.add %cast_to_index, %cast_to_index
%2 = spirv.IAdd %0, %cst1_i32 : i32
spirv.Branch ^bb1(%2 : i32)
^bb3: // pred: ^bb1
spirv.mlir.merge
}
spirv.Return
}
}
but it still fails with the same error.
Seems like I’m clearly missing something. I’d appreciate any help! Thanks!