[llvm-dev] questions about legalize type for vector (original) (raw)

Craig Topper via llvm-dev llvm-dev at lists.llvm.org
Sat May 16 20:42:49 PDT 2020

Those are the actions for the type legalizer. They specify how to legalize a type that has no supported operations and isn't assigned to any register class by your target. The action will be applied to every operation on that type.

I assume v32i16 is otherwise supported for your target and only division is missing. If that's the case you'll need to define a Custom lowering operation for your target. So you'll need to call setOperationAction(ISD::SDIV, v32i16, Custom) from your TargetLowering constructor. Then write custom code in LowerOperation to custom handle v32i16 ISD::SDIV. From there you can split the operands, SIGN_EXTEND each to v16i32 do the SDIV, TRUNCATE the results back to v16i16, and use a CONCAT_VECTORS to join them back to v32i16.

~Craig

On Sat, May 16, 2020 at 7:23 PM 林政宗 via llvm-dev <llvm-dev at lists.llvm.org> wrote:

Hi,

I am writing a new backend and I met some problem. I want to support in IR: sdiv v32i16 %a, %b. But the target only support sdiv v16i32 %a, %b natively. Could I promote v32i16 to v32i32, split v32i32 to two v16i32 , truncate v16i32 to v16i16 and merge two v16i16 into one v32i16? Is this way possible? I saw the code fragment in TargetLowering.h: ============================================================ 169 /// This enum indicates whether a types are legal for a target, and if not, 170 /// what action should be used to make them valid. 171 enum LegalizeTypeAction : uint8t { 172 TypeLegal, // The target natively supports this type. 173 TypePromoteInteger, // Replace this integer with a larger one. 174 TypeExpandInteger, // Split this integer into two of half the size. 175 TypeSoftenFloat, // Convert this float to a same size integer type. 176 TypeExpandFloat, // Split this float into two of half the size. 177 TypeScalarizeVector, // Replace this one-element vector with its element. 178 TypeSplitVector, // Split this vector into two of half the size. 179 TypeWidenVector, // This vector should be widened into a larger vector. 180 TypePromoteFloat, // Replace this float with a larger one. 181 TypeSoftPromoteHalf, // Soften half to i16 and use float to do arithmetic. 182 }; ============================================================= I don't quite understand the action TypeWidenVector. What does it do? Does this action do like promote v32i16 to v32i32? If this way is possible, where should I set the LegalizeTypeAction in the source code? Is it in the constructor of class XXXTargetLowering? And How could I set the action to manipulate the process as I want? Thanks! Best regards, Jerry

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