[PATCH] D156350: [X86] Allow pre-SSE41 targets to extract multiple elements coming from the same DWORD/WORD super-element

[Simon Pilgrim via Phabricator via llvm-commits]

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Pre-SSE41 targets tended to have weak (serial) GPR<->VEC moves, meaning we only allowed a single extraction before spilling the vector to stack and loading the element instead. But this didn't make use of the DWORD/WORD extraction we had to use could extract multiple i8 elements at the same time.

This patch attempts to determine if all uses of a vector are element extractions, and works out whether all the extractions share the same WORD or (lowest) DWORD, in which case we can perform a single extraction and just shift/truncate the individual elements.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D156350

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/bitcast-vector-bool.ll
  llvm/test/CodeGen/X86/pr63108.ll
  llvm/test/CodeGen/X86/subvectorwise-store-of-vector-splat.ll

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