[PATCH] D73863: [X86] Custom isel floating point X86ISD::CMP on pre-CMOV targets. Eliminate ConvertCmpIfNecessary

[Craig Topper via Phabricator via llvm-commits]

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

If we don't have cmov, X87 compares write to FPSW and we need to
move the bits to EFLAGS to use as JCC/SETCC/CMOV conditions.

Previously this was done by calling ConvertCmpIfNecessary in
multiple places which would emit the extra code for the FNSTSW,
a shift, a truncate, and a SAHF instructions. Isel would then
select trunc+X86ISD::CMP to a FUCOM instruction that produces FPSW.

This patch centralizes all of the handling into a single custom
isel handler. This allows us to remove ConvertCmpIfNecessary and
a couple target specific ISD opcodes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73863

Files:
  llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/lib/Target/X86/X86ISelLowering.h
  llvm/lib/Target/X86/X86InstrFPStack.td
  llvm/lib/Target/X86/X86InstrInfo.td

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