[llvm] [RISCV][GISEL] legalize, regbankselect, and instruction-select G_PTRMASK (PR #73062)

[Craig Topper via llvm-commits]

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+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
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topperc wrote:

Should we test the ANDI case which is probably the more common use case for G_PTRMASK?

https://github.com/llvm/llvm-project/pull/73062