[llvm] [RISCV] Allow 64-bit fixed frame-offsets on RV64 (PR #201338)

[Craig Topper via llvm-commits]

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topperc wrote:

If we go through this path, the `if (Offset.getScalable())` check on line 286 will be false because we converted the scalable offset to a fixed offset. In that case, I don't think we call `mulImm`

https://github.com/llvm/llvm-project/pull/201338