[PATCH] D73859: [X86] Add custom lowering for lrint/llrint to either cvtss2si/cvtsd2si or fist.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: RKSimon, spatel.
Herald added subscribers: jfb, hiraditya.
Herald added a project: LLVM.

lrint/llrint are defined as rounding using the current rounding
mode. Numbers that can't be converted raise FE_INVALID and an
implementation defined value is returned. They may also write to
errno.

I believe this means we can use cvtss2si/cvtsd2si or fist to
convert as long as -fno-math-errno is passed on the command line.
Clang will leave them as libcalls if errno is enabled so they
won't become ISD::LRINT/LLRINT in SelectionDAG.

For 64-bit results on a 32-bit target we can't use cvtss2si/cvtsd2si
but we can use fist since it can write to a 64-bit memory location.
Though maybe we could consider using vcvtps2qq/vcvtpd2qq on avx512dq
targets?

gcc also does this optimization.

I think we might be able to do this with STRICT_LRINT/LLRINT as
well, but I've left that for future work.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73859

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/lib/Target/X86/X86ISelLowering.h
  llvm/lib/Target/X86/X86InstrAVX512.td
  llvm/lib/Target/X86/X86InstrFPStack.td
  llvm/lib/Target/X86/X86InstrSSE.td
  llvm/test/CodeGen/X86/llrint-conv.ll
  llvm/test/CodeGen/X86/lrint-conv-i32.ll
  llvm/test/CodeGen/X86/lrint-conv-i64.ll

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