[PATCH] D150798: [RISCV] Implement storeOfVectorConstantIsCheap hook to prevent store merging at VL=2

[Philip Reames via Phabricator via llvm-commits]

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In general, VL=2 vectors are very questionable profitability wise.  For constants specifically, our inability to materialize many vector constants cheaply biases us strongly towards unprofitability at VL=2.

This hook is very close to the x86 implementation.  The difference is that X86 whitelists stores of zeros, and we're better off letting that stay scalar at VL=2.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D150798

Files:
  llvm/lib/Target/RISCV/RISCVISelLowering.h
  llvm/test/CodeGen/RISCV/rvv/combine-store.ll

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