[llvm] [RISCV] Remove custom isel lowering of i64 to Zilsd load/store. (PR #169067)

[Craig Topper via llvm-commits]

topperc wrote:

> I'm not sure how I feel about this.
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> I do see that we can still improve zilsd optimisations, to undo the regressions, but I also prefer that we keep the 64-bit operations as 64-bit operations, rather than breaking them apart during isel, only to put them back together again several passes later.
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> I do also see that removing this code means less to maintain.

Is using Zilsd worth the additional moves required for the even/odd pairing.

https://github.com/llvm/llvm-project/pull/169067