[PATCH] D110342: [x86] convert logic-of-FP-compares to FP logic-of-vector-compares

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: pengfei, craig.topper, lebedev.ri, RKSimon.
Herald added subscribers: hiraditya, mcrosier.
spatel requested review of this revision.
Herald added a project: LLVM.

This is motivated by the examples and discussion in:
https://llvm.org/PR51245
...and related bugs.

By using vector compares and vector logic, we can convert 2 'set' instructions into 1 'movd' or 'movmsk' and generally improve throughput/reduce instructions.

Unfortunately, we don't have a complete vector compare ISA before AVX, so I left SSE-only out of this patch. Ie, we'd need extra logic ops to simulate the missing predicates for SSE 'cmpp*', so it's not as clearly a win.


https://reviews.llvm.org/D110342

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/fcmp-logic.ll
  llvm/test/CodeGen/X86/lzcnt-zext-cmp.ll

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