[PATCH] D153865: [LoongArch] Add back SDNPSideEffect properties to CSR and IOCSR read ops

[WÁNG Xuěruì via Phabricator via llvm-commits]

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In general, CSR and IOCSR reads cannot be reordered, merged or otherwise
optimized, because:

- there may well be intervening writes between seemingly common expressions;
- the stateful entity behind a given (IO)CSR may well be volatile.

Confirmed to fix broken Clang Linux/LoongArch builds (dying when a
userspace process tries to use FPU, panicking when that process is init)
with this patch.

Fixes: https://github.com/llvm/llvm-project/issues/63549
Fixes: 2efdacf74c54 <https://reviews.llvm.org/rG2efdacf74c54a14ff72e9ab4b2e0707e5b3b86a8> ("[LoongArch] Add missing chains and remove unnecessary `SDNPSideEffect` property for some intrinsic nodes")


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D153865

Files:
  llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
  llvm/test/CodeGen/LoongArch/intrinsic-csr-side-effects.ll
  llvm/test/CodeGen/LoongArch/intrinsic-iocsr-side-effects.ll
  llvm/test/CodeGen/LoongArch/intrinsic-la64.ll

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