[PATCH] D119532: [RISCV] Extend sext.w removal pass to remove unused sign-extensions

[Mohammed Nurul Hoque via Phabricator via llvm-commits]

mohammed-nurulhoque created this revision.
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Current pass recursively searches **definitions** backwards to determine if a sext.w is redundant because the value is already in sign-extended form. An instruction propagates a sign-extended definition if giving it a sign-extended input yields a sign-extended output.

This patch adds recursively searching **uses** forwards to determine if bits 63:32 of sext.w result are not used, so it can be removed. An isntruction propagates sign-extended use if the lower word of its output is only dependent on the lower word of its input.

I have a pending patch dependent on this one that "fixes" other instructions (e.g. ADD -> ADDW) to make a sext.w redundant.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D119532

Files:
  llvm/lib/Target/RISCV/RISCVSExtWRemoval.cpp
  llvm/test/CodeGen/RISCV/sextw-removal.ll

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