[llvm] [RISCV][GISEL] Add legalizer for G_BSWAP (PR #70226)

[Fangrui Song via llvm-commits]

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@@ -68,77 +68,32 @@ body:             |
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY $x10
     ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(s32) = COPY $x11
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MaskRay wrote:

The MIR lacks some properties. I guess adding `tracksRegLiveness: true` and running `-global-isel -start-before=legalizer` will work.

https://github.com/llvm/llvm-project/pull/70226