[llvm] [RISCV][GISel] Instruction select for vector G_ADD, G_SUB (PR #74114)

[Jiahan Xie via llvm-commits]

jiahanxie353 wrote:

> > Hi, I'm stuck on [this part](https://github.com/llvm/llvm-project/blob/21b986637b950bb1762a38201223d62c4bca0dce/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp#L280C25-L280C71), where it tries to compare `Ty.getSizeInBits()`, which is a `vscale x s32` and `TRI.getRegSizeInBits(*RC)`, which is an `int 64`. It seems like there is no `>` overloaded to compare these two types. Is this issue expected?
> 
> Before the addition of scalable vectors, the size of scalars and fixed vectors is always known. For example an i32 is 32 bits, a float is 32 bits, and 4 x i32 is 4 * 32 bits. With the addition of scalable vectors, we do not know the size at compile time. The size of a type like `vscale x 1 x i32` depends on the value of `vscale`, which is a runtime constant, which makes the number of bits of that type unknown at compile time.
> 
> Instead of returning `unsigned` for the size of the type, we must return `TypeSize`, which is capable of representing that the size is scalable. Take a look at [this](f219e03f3c9bea4220925838c3d57d5a993d4d7a) patch which I added in order to make lowerFormalArguments work. You will likely need to make some unsigned -> TypeSize changes. For the exact case you show here, you probably want to take advantage of the `TypeSize::isKnownLT` function.

Thanks!
Seems like the link to the lowerFormalArguments patch is not working? Can you send again?

https://github.com/llvm/llvm-project/pull/74114