Pierre-vh added inline comments.
================ Comment at: llvm/lib/Target/AMDGPU/SIISelLowering.cpp:4819-4831 + // When we don't have 16 bit instructions, bf16 is illegal and gets + // softened to i16 for storage, with float being used for arithmetic. + // + // After softening, some i16 -> fp32 bf16_to_fp operations can be left over. + // Lower those to (f32 (fp_extend (f16 (bitconvert x)))) + if (!Op->getValueType(0).isFloatingPoint() || + Op->getOperand(0).getValueType() != MVT::i16) ---------------- arsenm wrote: > Pierre-vh wrote: > > arsenm wrote: > > > Pierre-vh wrote: > > > > arsenm wrote: > > > > > Pierre-vh wrote: > > > > > > arsenm wrote: > > > > > > > Pierre-vh wrote: > > > > > > > > arsenm wrote: > > > > > > > > > Pierre-vh wrote: > > > > > > > > > > arsenm wrote: > > > > > > > > > > > The generic legalizer should have handled this? > > > > > > > > > > It looks like those operations are not implemented in the > > > > > > > > > > generic legalizer, e.g. I get > > > > > > > > > > ``` > > > > > > > > > > Do not know how to promote this operator's operand! > > > > > > > > > > ``` > > > > > > > > > Right, this is the code that would go there > > > > > > > > Do I just copy/paste this code in that PromoteInt function, and > > > > > > > > keep a copy here too in LowerOperation? (not really a fan of > > > > > > > > copy-pasting code in different files, I'd rather keep it all > > > > > > > > here) > > > > > > > > We need to have the lowering too AFAIK, it didn't go well when > > > > > > > > I tried to remove it > > > > > > > I'm not following why you need to handle it here > > > > > > IIRC: > > > > > > - I need to handle FP_TO_BF16 in ReplaceNodeResult because that's > > > > > > what the Integer Legalizer calls (through CustomLowerNode) > > > > > > - I need to handle both opcodes in LowerOperation because > > > > > > otherwise they'll fail selection. They can be left over from > > > > > > expanding/legalizing other operations. > > > > > But why are they custom? We don't have to handle FP16_TO_FP or > > > > > FP_TO_FP16 there, and they aren't custom lowered. They have the same > > > > > basic properties. We have this: > > > > > > > > > > > > > > > ``` > > > > > setOperationAction(ISD::FP16_TO_FP, MVT::i16, Promote); > > > > > AddPromotedToType(ISD::FP16_TO_FP, MVT::i16, MVT::i32); > > > > > setOperationAction(ISD::FP_TO_FP16, MVT::i16, Promote); > > > > > AddPromotedToType(ISD::FP_TO_FP16, MVT::i16, MVT::i32); > > > > > ``` > > > > > > > > > > I'd expect the same basic pattern > > > > PromoteIntegerOperand, PromoteFloatOperand and PromoteIntegerResult > > > > don't handle FP_TO_BF16 and BF16_TO_FP, and unless we put a Custom > > > > lowering mode it'll assert/unreachable. > > > > I tried to make it work (for a while) using the default expand but I > > > > can't quite get it to work. It feels like there is some legalizer work > > > > missing for handling BF16 like we want to. > > > > Even though it's not ideal I think the custom lowering is easiest > > > What about Expand? that's where the implemented part is > > Last I tried, Expand will emit a libcall in many cases that we don't handle > Library call is supposed to be a distinct action now, the DAG only did about > 5% of the work to migrate to using it. This code can go to the default expand > action Does it need to happen in this commit? It'll delay the review quite a bit I think if other people have to review it If it needs to happen, when what do I need to do? Use the Expand action & fix the legalizer in places where it needs to be fixed? I feel like it might be better suited for a follow-up patch; I can create a task and pick it up when I come back from vacation if you want Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D139398/new/ https://reviews.llvm.org/D139398 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
